identification of ‘black-and-white’ storm-petrels of the...

407© British Birds 100 • July 2007 • 407–442

Identification of ‘black-and-white’

storm-petrels of theNorth Atlantic

Robert L. Flood and Bryan Thomas

ABSTRACT This review article consolidates identification criteria for the sixspecies of ‘black-and-white’ storm-petrel recorded or claimed in the NorthAtlantic: European Storm-petrel Hydrobates pelagicus,Wilson’s Storm-petrelOceanites oceanicus, Leach’s Storm-petrel Oceanodroma leucorhoa, Madeiran

Storm-petrel O. castro, Black-bellied Storm-petrel Fregetta tropica and White-bellied Storm-petrel F. grallaria. Established knowledge is updated with fresh

insights and illustrated with instructive digital images.We have two aims:(a) to support County Recorders in Britain now responsible for evaluating

Wilson’s Storm-petrel submissions; and (b) to bring to a wider internationalaudience current understanding about identification of North Atlantic ‘black-

and-white’ storm-petrels.The article has two main sections: (a) a generaldiscussion about identification of the storm-petrels under review; and

(b) detailed species accounts, and information on how each species can bedistinguished from the other five species (though white-bellied Fregetta

storm-petrels remain problematic).A template that outlines our view of whatconstitutes a sound submission of a reportable ‘black-and-white’ storm-petrel

is proposed.The main text is supported by ten appendices covering size illusionand exaggeration, factors of scale, angle of view, descriptive terminology for flight behaviour, chum and chumming, and wear, moult and bleaching.

We focus on vessel-based observation since, realistically, this is the optimalmeans of getting to grips with storm-petrels in the field and is the main

source of our experience. Land-based observation rarely affords the views essential to apply the finer points of this presentation.

Observation and identification oftubenoses (Procellariiformes) became‘fashionable’ in Britain in the 1980s

with publication of Peter Harrison’s two seabirdguides (Harrison 1983a, 1987) and the advent

of pelagic trips into the Western Approachesaboard MV Chalice (with Harrison, from 1986to 1988), and on RMV Scillonian III(1989–2004). These pelagic trips enabled manybirders to experience North Atlantic tubenoses

An observer who has once had the good fortune of watching the two species [Wilson’s and Leach’s Storm-petrels] together can thereafter distinguish them almost as far away

as the birds can be seen (Murphy 1915).

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408 British Birds 100 • July 2007 • 407–442

Identification of ‘black-and-white’ storm-petrels

at close quarters and made possible the rareopportunity to photograph them. In those ‘earlydays’, Wilson’s Storm-petrel Oceanites oceanicuswas the Holy Grail that tempted many British‘listers’ to participate in what was for some astomach-wrenching venture to sea.

However, from 2000, observations fromregular short-range pelagic trips off the Isles ofScilly between June and September establishedthat Wilson’s is, in fact, a regular though scarcesummer and early autumn passage migrant inScillonian waters, and is not a sacred rarity (seeAppendix 1). In 20 years, the status of Wilson’sStorm-petrel plummeted from Holy Grail toone where it was no longer considered as anational rarity (as from 1st January 2006;Rogers et al. 2005). Suddenly, assessing reportsof Wilson’s became the responsibility of CountyRecorders, but there has been no recent sub-stantive consolidated identification update onWilson’s and similar so-called ‘black-and-white’North Atlantic storm-petrels to aid decision-making at a county level.

Furthermore, interest in storm-petrels hasescalated in tandem with multiplying pelagictrips from many ports, on both sides of theNorth Atlantic. Knowledge has accrued aboutwhere and when to see them, while the mix ofchum and methods of chumming haveimproved, bringing more storm-petrels evencloser to observers and photographers (seeAppendix 2). The combination of more pelagictrips, close proximity of storm-petrels andimprovements in digital photography hasyielded superb images of storm-petrels at sea,including many published for the first timehere. Insights into the identification of storm-petrels have arisen through critical analysis ofdigital stills and videos in combination with at-sea observations. Conversely, unhelpful mythshave been propagated (see Appendix 3). So, inaddition to supporting local recorders inBritain, there is an international need for areview article on ‘black-and-white’ NorthAtlantic storm-petrels, integrating establishedknowledge with fresh insights and new photo-graphic material.

North Atlantic ‘black-and-white’ storm-petrelsFour species of ‘black-and-white’ storm-petreloccur regularly in the North Atlantic: EuropeanStorm-petrel Hydrobates pelagicus, Wilson’sStorm-petrel Oceanites oceanicus, Leach’sStorm-petrel Oceanodroma leucorhoa, and

Madeiran Storm-petrel O. castro. Europeanbreeds during the northern summer in thenortheast Atlantic and the Mediterranean, win-tering mainly off the west coast of Africa.Wilson’s is a circumpolar breeder along theAntarctic coastline as well as on sub-Antarcticislands during the southern summer and part ofthis population winters in the North Atlantic(another population breeds in the Chileanfjords). Leach’s breeds during the northernsummer in the northwest and northeast regionsof the Atlantic and winters mainly in regions oftropical convergence (there are also populationsin the Pacific). Madeiran breeds throughout theyear in the tropical and subtropical Atlantic; it isdispersive and/or migratory and recorded in thewestern Atlantic from Brazil to Canada (thereare also populations in the Pacific). However, tothe north and east of its Atlantic breedingrange, Madeiran is an extreme vagrant toWestern Europe, except Portugal where there isa relatively small offshore breeding colony, esti-mated at c.50 pairs by Brooke (2004), andc.200–400 pairs in BWPi (2006).

In western Europe, including Scandinavia,vagrant Madeiran Storm-petrels have beenrecorded from Britain (one, November),Finland (one, January), France (one, August;two, October), Ireland (one, October), Spain(singles in January, February, June andNovember and two in July), and Switzerland(one, December) (Appendix 4). The data aredifficult to interpret because of the limitednumbers, while there is a complication withMadeiran Storm-petrels breeding in the Azores,where two distinct populations ‘time-share’burrows, each having non-overlapping breedingand dispersal periods (Friesen et al. 1998; Mon-teiro & Furness 1998; Sangster 1999). The datatentatively suggest that Madeiran is most likelyto occur as a vagrant in western Europe duringthe storm-prone months from October to February (often among other wreckedseabirds). Pelagic or land-based (tape-lured)records in summer for Spain and France mayrelate to ‘wanderers,’ probably from the smallcolony off Portugal but conceivably fromanother, larger North Atlantic colony.

In addition, a Black-bellied Storm-petrelFregetta tropica, presumably from the SouthAtlantic populations, was seen and pho-tographed c.70 km southeast of Oregon Inlet,North Carolina, on 31st May 2004 (Guris et al.2004). Another was seen and photographed

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nearby in the Gulf Stream off Cape Hatteras on16th July 2006 (www.patteson.com). A White-bellied Storm-petrel F. grallaria was reportednorth of the Cape Verde Islands on 17th August1986 (Haase 1988; Clarke 2006). However, thedescription is brief and there is some doubtwhether Black-bellied can be excluded (BWPi2006). Moreover, there is confusion in the liter-ature regarding the white-bellied Fregettastorm-petrels that breed in the Tristan daCunha group (here taken to include GoughIsland). It is possible that a population of white-bellied Black-bellied Storm-petrels breedsalongside a population of White-bellied Storm-petrels, making the field identification of anywhite-bellied Fregetta storm-petrel in the NorthAtlantic extremely difficult (Appendix 5).Nonetheless, both Fregetta storm-petrels arepotential vagrants to British waters.

IdentificationAt-sea identification of seabirds involves uniquedifficulties. Encounters are often extremelybrief; on all but large and steady vessels tele-scopes are redundant; and changeable light andweather conditions can dramatically ‘manipu-late’ context and the impressions gained. Fur-thermore, with tubenoses we are dealing with acomplex and often subtle plumage problema-tique since petrels are ‘clad in plumage that issome combination of black, white and shades ofgrey and brown’ (Brooke 2004). These factorsalso pose unique difficulties for rarities com-mittees (Bradshaw 2002). Cryptic plumage andother difficulties are cues for a methodicalapproach to at-sea storm-petrel identificationand we consider five key issues, which are dis-cussed below: jizz and analysis, size, structure,plumage, and flight behaviour.

Jizz and analysisAs we experience it, the process of storm-petrel

identification unfolds as follows. Size, structure,plumage, and flight behaviour at first sightcombine into a whole first-interpretation, or‘jizz’. Jizz interpretation facilitates a ‘first-stab’ atidentification: for example, ‘Oceanodroma at theback of the slick!’ or ‘Oceanites-like “stormy”approaching from down-wind!’ Dunne (2006)attempted to convey jizz using catchphrases thatare familiar to all. Those relevant to this articleinclude: Wilson’s ‘dances with waves’, Leach’s isthe ‘crazed or drunken Nighthawk of the sea’,and Madeiran is the ‘plain dark storm-petrel’(p. 112). Similes also offer an effective way ofcapturing the essence of a storm-petrel (table1). The idea of using catchphrases and similesto summarise the quintessential character of astorm-petrel can be very effective but there arecaveats. First, jizz interpretation breaks down inextreme circumstances at sea, such as duringstrong and gusty winds. Second, jizz is modifiedwhen the bird’s flight feathers are heavily wornand/or in moult (Appendix 6). Third, jizz inter-pretation alone, like pigeonholing, runs the riskof over-simplification. Hence, there also is needto employ an analytical approach that gets togets to grips with finer details of storm-petrelidentification. Our analytical approach com-prises four main tasks: judging size, notingstructure, describing plumage, and recountingflight behaviour. If the four tasks can be per-formed satisfactorily, then most storm-petrels(with the exception of white-bellied Fregettastorm-petrels) encountered in the NorthAtlantic may be identified with confidence.

SizeTwo inter-related size judgements are desirable:(a) relative body lengths and wingspans of theunidentified storm-petrel and nearby storm-petrels or other seabirds; and (b) actual bodylength and wingspan of the storm-petrel (table2).

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Table 1. Similes for the six species of ‘black-and-white’ storm-petrel recorded or claimed in the NorthAtlantic: European Storm-petrel Hydrobates pelagicus,Wilson’s Storm-petrel Oceanites oceanicus, Leach’s

Storm-petrel Oceanodroma leucorhoa, Madeiran Storm-petrel O. castro, Black-bellied Storm-petrel Fregetta tropica and White-bellied Storm-petrel F. grallaria (* denotes comparison found in recent literature).

Genus Species Like a …

Hydrobates European small bat (Chiroptera)*Oceanites Wilson’s smallish hirundine, in particular a Barn Swallow Hirundo rustica*.Oceanodroma Leach’s & respectively, Common Nighthawk Chordeiles minor* and European

Madeiran Nightjar Caprimulgus europaeus*Fregetta Black-bellied & well-accomplished exhibition skateboarder (in both cases)

White-bellied

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Ideal circumstances that facilitate accuratejudgement of actual and relative body lengthand wingspan involve observers with reasonableexperience on a familiar vessel in known waterswith well-known comparison species (i.e. ‘sea-birders on their patch’). Nonetheless, makingsize comparisons between storm-petrel speciesis challenging. We have experienced two size-illusion phenomena: that between storm-petrelspecies at sea (Appendix 7); and that resultingfrom factors of scale (Appendix 8).

Structure There are five key structural features to note:(a) wing shape, (b) tail shape, (c) toe projec-tion, (d) body build, and (e) bill shape and proportions.

Wing shapeThis differs among species and changesaccording to flight behaviour (see below). Whena storm-petrel is travelling, or feeding bygliding, skimming and surface-snatching, notethe following: the angle at the carpal joint –from smoothly rounded, to shallow angle, todeep angle; shape of trailing edge – from

straight to angular; and head-on wing profile –either straight or bowed in a shallow ‘M’. Somespecies feed by hanging in the air above fooditems, with wings held at an angle ranging frombelow the body to above the body in a V-shapewhile the primaries are fanned, making thetrailing edge of the hand rounded and thewings seemingly paddle-shaped. Note the angleof the wings relative to the body, ranging fromslightly depressed, through horizontal and aflattened-V, to an erect-V. Some species hoverrather than hang. The paddle shapes mentionedabove differ somewhat among species as a resultof different wing formulae; these shapes are notwell documented and in any case are difficult toassess in the field, although photographs mayhelp.

Tail shapeThis also differs among species and changesaccording to flight behaviour (see below). Thetail is normally closed when travelling (speciesdependent) and fanned while hanging or hov-ering above food items. Whether the tail isclosed or fanned, note whether the corners arerounded or squared-off, and note whether the



Table 2. Part (i) shows actual body length and wingspan (in mm) of ‘black-and-white’ storm-petrels recordedor claimed in the North Atlantic (European Storm-petrel Hydrobates pelagicus,Wilson’s Storm-petrel Oceanitesoceanicus, Leach’s Storm-petrel Oceanodroma leucorhoa, Madeiran Storm-petrel O. castro, Black-bellied Storm-

petrel Fregetta tropica and White-bellied Storm-petrel F. grallaria). Sources: (1) BWPi (2006); (2) Blomdahl et al.(2003); (3) Marchant & Higgins (1990); (4) average of the median figure in sources (1)–(3); this figure is used

in species accounts below.

Part (ii) shows relative body length and wingspan of the same species, calculated from column 4 in part (i).For example, the relative body length and wingspan of European and Wilson’s are, respectively, 1.08 and 1.05; in other words, the body length of Wilson’s is, on average, 1.08 times larger than that of European

and the wingspan is 1.05 times larger.

(i)Body length Wingspan

Ref. 1 2 3 4 1 2 3 4

European 140–180 150–160 na 158 360–390 370–410 na 383Wilson’s 150–190 160–185 150–190 171 380–420 380–420 380–420 400Madeiran 190–210 190–210 na 200 440–460 430–460 na 448Black-bellied 190–210 na 200 200 440–470 na 450–460 455White-bellied 190–210 na 180–220 200 440–470 na 460–480 462Leach’s 190–220 180–210 190–220 202 450–480 430–480 450–480 462

(ii)Relative body length (above species’ names)

European 1.08 1.27 1.27 1.27 1.281.05 Wilson’s 1.17 1.17 1.17 1.181.17 1.12 Madeiran 1.00 1.00 1.011.19 1.14 1.02 Black-bellied 1.00 1.011.21 1.16 1.03 1.02 White-bellied 1.011.21 1.16 1.04 1.02 1.01 Leach’sRelative wingspans (below species’ names)

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tail-tip is rounded, square-ended, or forked, andthe depth of any fork from deep, to shallow, tomerely concave. Note also that wear and moultaffect both wing shape and tail shape(Appendix 6).

Toe projectionRelative leg length (including feet and toes) totail length varies significantly among species.Travelling storm-petrels hold their legs mainlystraight-out, immediately under the tail andtucked beneath the undertail-coverts. Conse-quently, the toes project considerably beyondthe tail-tip in species with relatively long legs(e.g. Wilson’s) but generally not in species withrelatively short legs (e.g. Leach’s). Note thatstorm-petrels rarely retract their legs while trav-elling (but if long-legged species retract theirlegs, then toe projection is obviously elimi-nated) and also that the extent of toe projectioncan alter with moult and wear. Species that nor-mally do not show a toe projection might do sowhen the tail is heavily worn or in moult (BWPi2006).

Body buildThis varies among species, from short andcompact like European, to long yet chunky likeMadeiran, to fat and compact like Black-belliedand White-bellied.

Bill shape and proportions Significant variation is found across the sixspecies. Note the length and depth of basal anddistal halves, overall curvature, and extent of thehook at the bill tip. Gaining unequivocal viewsand logging details of bill shape and propor-tions is very difficult at sea and often unsatisfac-tory in video footage. High-quality digital stillsare the most reliable way of capturing billdetails.

PlumageThere are five key plumage features to describe:(a) upperwing-covert bars; (b) underwing-covert and axillary panels; (c) white on rump,uppertail- and undertail-coverts and rearflanks; (d) white on belly; and (e) generalcolour and colour tones. Plumages of sexes andages are essentially alike in storm-petrels andthere are no seasonal differences, but greycolour tones become paler and black-browntones browner as feathers become worn andbleached. Fresh juveniles of some species show

narrow white fringes to certain feathers, but thisrapidly wears away and is of no consequence tofield identification.

Upperwing-covert bars Length, width and shape, prominence, colourand colour tone of wing-covert bars vary con-siderably among species. Prominent wing-covert bars stand out at long range. The mainfeather tract involved is the greater coverts, butbars sometimes cross feather tracts includinggreater, median and lesser coverts, especially atthe distal end, which broadens the bars in thatarea and extends them towards the leading edgeof the wing. Note: length of covert bars, eitherreaching the leading edge or falling short of it;width (either narrow – pale tips to greatercoverts, medium – pale greater coverts, or broad– bar covering several feather tracts); andresulting shape – respectively like a pencil-line,roughly rectangular, or a tear-shape, broadeningdistally. Also note prominence, from bright todull, as well as colour and colour tones (in con-junction with state of wear).

Underwing-covert and axillary panels This region is variably pale in the six speciesand to some extent varies individually. Promi-nent panels stand out at long range. The mainfeather tracts involved are the greater-under-wing and greater under-primary coverts andaxillaries, but other feather tracts may beincluded. Note whether this region appearsdark, bronze-flushed, pale or white. Some whitepanels gleam, whereas others appear ‘dirty’ inparts, which should be noted. The dirty lookoccurs when wholly or partly dark feathers areadmixed, typically among the outer greaterprimary coverts. High-quality digital stillsshould reveal the precise pattern.

White on rump, uppertail- and undertail-covertsand rear flanksThe extent and shape of white in this regionvaries considerably between some species, whilein others it is similar. In species where white onthe upperside extends to the underside, thewhite always seems to be on view, even at con-siderable range, whether the storm-petrel is inflight or sat on the sea. Conversely, with specieswhere the white barely extends to the underside,the white in this region is at best on view occa-sionally and may be hard to see, even at closerange. Note whether the white patch is visible



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across the width of rump and uppertail-covertsand whether it is narrow or broad, roughlysquare or rectangular, and U-shaped or V-shaped (a V-shape is created by dark feathers inthe central/upper area of an otherwise whiterump). Note whether white extends to theundertail-coverts and rear flanks.

White on belly Look for white on the belly, especially if astorm-petrel seems fat and compact. A whitebelly immediately suggests Fregetta storm-petrels from the South Atlantic or somethingastonishing – such as White-vented Storm-petrel Oceanites gracilis, the miniaturisedWilson’s Storm-petrel of the Pacific! Before col-lapsing, note whether the whole belly is whiteand whether the borders with the black-brownupper breast and undertail-coverts (if dark) arestraight and clean-cut or smudgy. Note any evi-dence of a dark central belly stripe and whetherbroken or complete; if the latter, note whether itunmistakeably connects the dark breast to theundertail-coverts. Still photographs are the bestway to clinch the pattern of the underside (evenif somewhat out-of-focus).

General colour and colour tonesAlthough all of the ‘black-and-white’ storm-petrel species can be described as black-brown(not black) and white, the extent to which blackdominates brown is different in each speciesand the tone of the black-brown ranges fromcool to warm. Note the black-brown colour andcolour tones of head, body, wings and tail, eventhough they vary according to light conditions.Where possible, compare colour tones directlywith those of other storm-petrels, which allowscomparison under similar light conditions. Bearin mind that colour tones change with featherage and that exposed feathers of head, body,wings and tail become browner with age. Palefeathers that form upperwing-covert barsbecome paler and more bleached with time, andmay even begin to disappear with age and wear.

Flight behaviourThere are two main flight behaviours to note:travelling (including migration, flights betweenfeeding grounds and breeding colonies, and ageneral search for food) and feeding. Storm-petrels feed on items found on or just below thesea surface and, once food has been located, thebird must manoeuvre over it, and seize, snatch

or pick at the prey, even dive for it. The basictask is the same for all species, but the way it iscarried out differs among species. Flight isclearly affected by wear and moult of flightfeathers (Appendix 6). Terminology has evolvedto describe flight behaviour of storm-petrelsand several of the terms (explained in Appendix9) may be used to portray each species: e.g. atravelling Wilson’s in moderate wind might bedescribed as having ‘purposeful direct flight onstiff wings with steady wingbeats close to the seasurface for an extended period’, while a travel-ling Leach’s in similar conditions might bedescribed quite differently and have ‘erraticflight on elastic wings with deep wingbeats inter-spersed with shearing glides’.

Sealing the identificationSealing the identification of a North Atlantic‘black-and-white’ storm-petrel is, in principle,straightforward given sound basic knowledgeand reasonably close and extended views, inmoderate to fair weather conditions (thoughwhite-bellied Fregetta storm-petrels remainproblematic). Photographic stills help sincethey capture the detail of structure andplumage not always visible at sea. Equallyimportant, video footage captures flight behav-iour for subsequent critical analysis. Stills andvideo add substance to a rare storm-petrelclaim (e.g. Flood et al. (2004) and Stephenson etal. (2007a) in the rediscovery of the NewZealand Storm-petrel Pealeornis maoriana orGuris et al. (2004) in the identification of a pre-sumed White-bellied Storm-petrel, subse-quently revealed through stills to be the NorthAtlantic’s first Black-bellied). However,although highly desirable, we do not believethat photographs are in every case essential fora rare storm-petrel to be accepted by a raritiescommittee.

We acknowledge that, with storm-petrels, nosingle feature is incontestably diagnostic. Jizz isa subjective measure. Judgement of size isimprecise and subject to size illusion andfactors of scale. Wing and tail shapes alter withmoult and wear. Plumage varies with moult,wear, bleaching, and aberration (and not allplumages are fully understood). Flight behav-iour is influenced by moult, wear and windstrength. However, a suite of features allpointing to one species with no contradictoryevidence may, in many cases, be taken as diag-nostic (see table 3 below). If observers are suffi-



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ciently experienced and attain satisfactoryviews, then a well-prepared submissionfocusing on the key features discussed here,preferably supported by photographs and/orartwork, will, in most cases, make decision-taking comparatively problem free.

Accordingly, our notion of a sound storm-petrel description is one that sets out the cir-cumstances of an observation and thenconcentrates on the following particulars:

• Size of vessel, range of storm-petrel, heightof observation point above sea surface andthus angle of view (Appendix 10).

• Jizz, animated through catchphrases orsimiles (table 1), or similar phrases that res-onate with the observer’s experiences.

• Actual body length and wingspan, relativebody length and wingspan compared withother storm-petrels (and seabirds) present atthe time (table 2), but with awareness of sizeillusion and factors of scale (Appendices 7 &8).

• Structure in terms of (a) wing shape, (b) tailshape, (c) toe projection, (d) body build, and(e) bill shape and proportions, all with refer-ence to moult and wear (Appendix 6) andangle of view.

• Plumage details of (a) upperwing-covertbars, (b) underwing-covert and axillarypanels, (c) white on rump, uppertail- andundertail-coverts, and rear flanks, (d) whiteon belly, and (e) general colour and colourtones, all with reference to angle of view.

• Flight behaviour, specifying whether travel-ling or feeding, employing common termi-nology (Appendix 9) or some otherwell-defined terminology, noting the impactof moult and wear on flight behaviour whererelevant (Appendix 6).

• Photographs and/or artwork.

• Explain how other storm-petrel species wereeliminated.

Species accountsThese describe in detail the six storm-petrelspecies in terms of taxonomy, Atlantic rangeand movements, and the five key identificationissues introduced above. Species accounts areconstructed from our observations at sea,analysis of structure and plumage using our stillphotographs, analysis of flight behaviour usingour video footage, all in conjunction withextant knowledge summarised in Naveen

(1981–82), Harrison (1983b), Marchant &Higgins (1990), Enticott & Tipling (1997),Sibley (2000), Shirihai (2002), Brooke (2004),BWPi (2006) and Onley & Scofield (2007).Several common characteristics are summarisedseparately. Accounts concentrate on features rel-evant to vessel-based observation and identifi-cation, except where wing structure isdescribed.

Common characteristicsAll six species share the following characteris-tics. They remain exclusively in the lowest 10 mof airspace above the sea surface; many remainin the lowest 5-m band and some occur mostlyin the lowest 2 m. All species have 11 primariesalthough the outermost (P11) is minute andnot relevant to this discussion, so P10 is takenas the effective outermost primary. When birdsfeed by hovering or hanging, the primaries arefanned, yielding paddle-shaped wings, theactual shape of the ‘paddle’ being determined bythe wing formula. Remiges and rectrices aredarker than wing-coverts and body feathers.Bill, legs and feet are black (although Wilson’salone has yellow foot-webbing). All are nor-mally silent at sea, save for occasional quietchattering among feeding flocks of Wilson’s(and perhaps other species).

European Storm-petrelTaxonomy Recent research suggests that thisspecies may be polytypic, with nominate pelag-icus in the Atlantic and H. p. melitensis in theMediterranean (Lalanne et al. 2001; Cagnon etal. 2004).Atlantic Breeds northeast Atlantic and Mediter-ranean, April–September. Dispersal mainlytransequatorial, on eastern side of Atlantic, Sep-tember–November. Movement of Mediter-ranean birds is unclear and at least some remainthere into the northern winter. Atlantic birdswinter west coast of Africa as far south as SouthAfrica, mainly in boundary zones between shelflittoral and deep ocean, November–March. Sig-nificant return passage off western Africa,March–April. The return of immature non-breeders to colonies is more leisurely whileothers, perhaps the youngest birds, remain inwaters along coasts of western Africa andsouthern Europe during breeding season.Vagrant to Atlantic seaboard of USA (ninerecords to end of 2006; www.patteson.com).Jizz Like a small bat.



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Identification of ‘black-and-white’ storm-petrelsBr

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Size Body length 158 mm. Wingspan 383 mm.Structure Wing shape Wing formula: P9 longest;P10 6–13; P8 1–3; P7 7–12; P6 16–19; P1 56–66mm shorter. Outer primary pointed in juve-niles, less so if worn, rounded in adults. Whentravelling, wings short and broad, wing-tipsblunt-ended, with both leading and trailingedges strongly angular. Head-on travellingprofile Wings normally slightly bowed formingshallow-M, arms and hands quite short. Tail

shape Short, can look square, though gentlyrounded; clearly rounded when fanned. Toe pro-jection None. Body build Compact, with shortbody. Bill shape and proportions At sea lookssmall. At close range short, though length anddepth are in proportion, slightly decurved andhooked; nasal tubes 40% of bill length.Plumage General colour and colour tonesDarkest North Atlantic storm-petrel. In freshplumage looks sooty-brown, but bleaches



164. (Left) Uppersides and undersides of the four regular ‘black-and-white’ storm-petrels of the North Atlantic,all roughly to scale, and to scale with plate 165. Top European Storm-petrel Hydrobates pelagicus, off Scilly,August 2004; upper middle Wilson’s Storm-petrel Oceanites oceanicus, off Scilly, July 2005; lower middle

Madeiran Storm-petrel Oceanodroma castro, off St Helena, April 2006; bottom Leach’s Storm-petrel O. leucorhoa,Equatorial Atlantic 0°00.000’S, 17°33.462’W,April 2006. Compare differences between the wing shapes;tail shapes; toe projection; upperwing-covert bar, underwing-covert and axillary panels, white on rump,uppertail- and undertail-coverts, and rear flanks.The white underwing panel of European Storm-petrel

is more striking than shown here when feathers are fresh.

[Footnote: A DVD containing movie footage of all six ‘black-and-white’ storm-petrels plus White-faced Storm-petrelPelagodroma marina, with a focus on flight behaviour, is available from Bob Flood, while digital stills of the same species,focusing on plumage and structure, are available from Bryan Thomas. Please use the contact details on p. 000.]

165. Uppersides and undersides of the two Fregetta species, all roughly to scale as well as to scale with plate 164.Top Black-bellied Storm-petrel F. tropica, Drake Passage, March 2006; bottom White-bellied Storm-petrel F. grallaria

(see Appendix 5), off Tristan da Cunha group, March 2006. Compare extent of toe projection (presumably legsretracted on Black-bellied Storm-petrel underside shot); upperwing patterns (contrast between species normally

greater than shown here), and underbody patterns.Br

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browner with age. Close up, paler and greyer onforehead and chin, browner below, with upper-body feathers darker than upperwing-coverts.Fresh juveniles have narrow whitish edges toupperpart feathers that wear off quickly. Upper-wing-covert bars At range, apparently uniformdark upperwings without covert bars. Close-up,greater coverts form very dull bars, a little moreobvious when bleached, but never shows broadpale bars. At close to medium range, brown-cream pencil line along tips of greater coverts(outer webs fringed pale), whitish and more

pronounced on autumn juveniles, but thiswears off quickly. Underwing-covert and axillarypanels In fresh plumage, eye-catching whitepanels in flight, even at long range. Photographsof birds off Scilly reveal greater under primarycoverts white with dark tips, greater underwing-coverts white, and axillaries dark with whitetips. Markings less obvious in worn birds, whencan be tricky to see, even at medium to closerange. White on rump, tail-coverts and rearflanks Lower rump feathers sooty-brown withwhite tips, uppertail-coverts white, longest with

black tips, whichcombine to give aroughly rectangular,well-defined, bold and(from above) slightlyU-shaped whiterump-patch. Patchextends to lateralunder ta i l -cover t s ,which are white withblack tips, and to rearflanks. In flight, whitepatch seeminglyalways in view what-ever the angle ofobservation; alsovisible when sat onsea at moderatelyclose range. White onbelly None.Flight behaviour Fliesmostly within 2 m ofsea surface, but occa-sionally up to 5 m.Travelling Flight char-acterised by fast,shallow, bat-like flut-tering wingbeats (hasfastest wingbeats ofthe six species) inter-spersed with occa-sional short glides.Sometimes casuallyzigzags, may shear instrong wind. Pre-sumed migrantsobserved in Octoberfrom headlands inScilly, flying directlyinto strong wind,made good headway.In contrast, Leach’s



166. European Storm-petrel Hydrobates pelagicus, off Scilly, July 2005. Storm-petrelsrelish tiny pieces of fish liver used in chum! To collect the liver, this European hovered

above it, using feet as stabilisers, dipped down to seize it, then quickly moved on,repeating this manouevre many times in quick succession. Note the paddle-shapedwings, short legs, white on the rump and uppertail-coverts extending to undertail-

coverts and rear flanks, and white underwing-covert and axillary panel.

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observed in similar conditions was unable toprogress directly into oncoming wind. FeedingPatrols area of food source such as a slick indashing and excited fashion, zigzagging backand forth, twisting and turning. When foodlocated comes to a dead halt, is briefly forcedupwards in so doing, then drops and, facinginto wind, hovers over food item with wingsnormally held in an erect V-shape (far moreerect than Wilson’s), using feet as stabilisers,dips head down and seizes food, then moves on.‘Hovers, dips, seizes and moves on’ repeatedlyand in quick succession. Hovering may beextended to perhaps four seconds, at whichtime engages in foot-pattering proper. Hoveringdifficult with little breeze, so instead of foot-pattering utilises body buoyancy by virtuallysitting on sea surface, and hangs by holdingwings normally in an erect V-shape, surface-seizes and moves on. ‘Sits, hangs, seizes andmoves on’ repeatedly and in quick succession.Off South Africa, also recorded diving to collectfood items (Griffiths 1981). Follows in the wakeof vessels and associates with feeding cetaceans.Overall impression Small, compact, dark, busyand seemingly restless; flashes white on under-wings in flight (less so when worn).

Wilson’s Storm-petrelTaxonomy Polytypic, with nominate oceanicus(sub-Antarctic islands south of Antarctic PolarFront) and O. o. exasperatus (Antarctic main-land and islands ofScotia Sea) of rele-vance here; some ofboth subspeciesbelieved to migrateinto North Atlantic.Atlantic BreedsDecember–Marchwith dispersal April–May, earlier ifburrows blocked byhard snow causingbreeding failures.Large northwardmovement WeddellSea by mid Marchand major emer-gence into sub-Antarctic waters inApril. Passage upboth sides ofAtlantic, mainly

west side, but allegedly not through centralAtlantic in any numbers; though Wilson’sobserved regularly March and April 2006 enroute to South Georgia, Tristan da Cunhagroup, St Helena, Ascension, then over theequator to Cape Verde Islands, last observedmid-way between Ascension and Cape VerdeIslands 12th April 2006 (pers. obs.). Also move-ment into Indian and Pacific Oceans. Arrivalnorthwestern Atlantic along coasts of USA fromthird week of April with concentrations in GulfStream off North America by end June.Common in Canary Current, but only smallnumbers reach northeastern Atlantic, e.g. offScilly June–September, where it becomes veryscarce from late August (Appendix 1). South-ward movement obvious September–October.Returns to colonies November–December.Immature non-breeders’ return to coloniesmore leisurely, others remain in tropical watersoff South America and South Africa duringbreeding season.Jizz Like smallish hirundine, especially BarnSwallow Hirundo rustica.Size Body length 171 mm. Wingspan 400 mm.Females said to be significantly larger thanmales in all proportions (Brooke 2004) thoughShirihai (2002) noted extensive overlap betweensexes. Subspecies exasperatus larger than nomi-nate, though may be clinal (Brooke 2004). Someslight variation in size noted off Scilly.Structure Wing shape P9 longest; P10 5–10; P8



167. Wilson’s Storm-petrel Oceanites oceanicus, Brown Bluff,Antarctic Peninsula, March2006.Wilson’s disperse from breeding grounds April–May, but earlier if burrows

become blocked by hard snow, as shown here (alongside Gentoo Penguins Pygoscelispapua), as breeding attempts then fail.

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3–8; P7 10–19; P6 21–30; P1 75–87 mm shorter.Outer primary pointed in juveniles, less so ifworn, rounded in adults. When travelling,wings medium length, broad with pointedwing-tips, leading edge smoothly curved,lacking sharp angular bend at carpal joint,trailing edge straight. Head-on travelling profileWings held out straight, giving stiff-wingedappearance, which is excellent clue whenWilson’s approaches vessel head-on from down-wind; also ‘arms’ short and ‘hands’ mediumlength. Tail shape Longish and slightly concave,outermost tail-feather 2–8 mm longer thancentral in exasperatus and 0–5 mm longer innominate; often looks square, corners rounded,tail slightly rounded when fanned. Toe projec-tion Long spindly legs, thus toes project wellbeyond tail-tip when travelling, visible atmedium range. Extent of projection varies tosome extent among individuals. Variation pos-sibly amplified if tail heavily worn or in moult.Note that rarely retracts legs into belly featherseliminating toe projection. Alexander Wilson,after whom the species is named, was the first torecord toe projection as a means to distinguishWilson’s from Leach’s (Wilson & Bonaparte1831; Boswall 1979). Body build Mediumlength, evenly proportioned length and girth,though longish tail with toe projection createslong rear-carriage look. Bill shape and propor-tions At sea looks small. Close up, medium-length, broad-based, slightly hooked, with nasaltubes 40% bill length.Plumage General colour and colour tones In freshplumage, warm-toned black-brown, butbleaches browner with age. Close up, chin andbelly slightly duller, crown and sides of headtinged grey. Upperwing-covert bars Obvious andbroad, start short of leading edge and extend tobody, formed by brown-grey, at times almostsilvery, greater coverts, white-fringed whenfresh (white fringes wear off quickly), andduller median coverts, these several tones palerthan lesser and marginal coverts. Covert barsbecome paler with age though may becomenarrower through feather wear. Underwing-covert and axillary panels Sooty-brown withbronze or (less frequently) pale flush, especiallywhen fresh, and rarely pronounced pale panels(pale panel in c. 1 in 250 birds Weddell Sea andSouth Atlantic March–April 2006, none in c.1,000 Antarctic Peninsula December 2006 andJanuary 2007; pers. obs.). White on rump, tail-coverts and rear flanks Lower rump feathers

black-brown tipped white, uppertail-covertswhite without dark spots on tips, togetheryielding a roughly rectangular, well-defined,bold and (from above) slightly U-shaped whitepatch. White patch extends to lateral undertail-coverts and rear flanks. Overall result is bold,broad white band that extends from rump tounderside, almost encircling tail. In flight, whiteseemingly always in view whatever the angle ofobservation, also visible when sat on sea (Sibley2000; pers. obs.). Aberrant bird with dark rumpseen near South Georgia (Bourne 1987). Curtis(1988) recorded bird with dark rump and sug-gested that it was an example of melanism.White on belly None. Yellow webbing of feet Vari-able amount of yellow on webbings of feet.Criticised as diagnostic feature by Boswall(1979) who states only seen in highly favourablecircumstances. Harrison (1983b) claimed seenonly twice in several thousand sightings, whileBlomdahl et al. (2003) stated visible only inexceptional circumstances. Our experience offScilly does not concur with these three com-mentaries, probably as a result of our chum-and-drift method (see Appendix 2). From ourvessels, Wilson’s often are at close range andobserved from a shallow angle of view. Whenbirds are feeding over a slick, positionedroughly between observer and sun, legs dan-gling, sunlight shines through and regularly‘illuminates’ yellow on webbings. We see yellowwebbings on most Wilson’s so positioned, evenwith moderate cloud cover.Flight behaviour Flies mostly within 2 m of seasurface, but may rise up to 5 m. Travelling Flightcan be strong, purposeful and direct, continu-ally flapping wings for extended periods oftime; occasionally veers from side to side, withspurt of rapid wingbeats broken by short glides.At other times seemingly less purposeful, andemploys skimming flight low over sea surfacewith shallow stiff wingbeats interspersed withsustained glides holding wings slightlydepressed, likened to a tropical butterfly (Blom-dahl et al. 2003). Feet rarely retracted whiletravelling. No vertical bounding as such, butrarely darts upwards, and is forced upwardswhen making a dead halt over food item.Feeding Flies low over sea surface with out-stretched stiff wings, gliding, skimming,running, skipping, hopping, sometimessplashing, while dipping head to snatch fooditems. May hang (rather than hover) over foodsource with sufficient breeze, facing into wind,



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wings often held in aflattened V-shape,though sometimeshorizontal, some-times more erect,with the angleostensibly deter-mined by windstrength (but muchflatter than forEuropean), wingspaddle-shaped, tailfanned and some-times raised slightlyupwards, head lifted,bill angled down,dipping head tosurface-seize or pullat floating food.Long spindly legsused in comicale x a g g e r a t e dbouncing over seasurface as if on apogo-stick. Such‘dancing’ is seem-ingly choreographedand unmistakeable!When dancing, staysover one spot ordrifts backwards orsideways with windor makes slowprogress into wind,sometimes dancingfor periods of manyminutes; often arcsback to origin offood source andstarts procedureagain. Arcing backtypical of Wilson’sfeeding over slickduring short-rangepelagic trips offScilly, but also wit-nessed in thesouthern hemi-sphere. Also makesshort, shallow dives;off South Georgia and south Shetlands timed atone or two seconds (from video). Follows inwake and alongside bow-wash of vessels; alsoassociates with feeding cetaceans.

Overall impression Small to medium-sized,evenly proportioned, warm-toned black-brown,with obvious upperwing-covert bars; accom-plished in flight.



168. Wilson’s Storm-petrel Oceanites oceanicus, South Georgia, March 2006.ThisWilson’s is hanging over a kelp bed, facing into a stiff breeze, wings held roughly

horizontal to back and semi-paddle-shaped, tail fanned and raised slightly upwards,long spindly legs used in comical, exaggerated bouncing over sea surface as if on a pogo stick, head lifted, bill angled down, about to dip head to surface-seize –

this ‘dancing routine’ seemingly choreographed.

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169. Wilson’s Storm-petrel Oceanites oceanicus, South Georgia, March 2006.ThisWilson’s (alongside the Wilson’s in plate 168) is feeding over a kelp bed, but has just

dived to collect a food item, and its tail is just about to submerge. Note that even from directly below, it is still possible to see white undertail-coverts.

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Leach’s Storm-petrelTaxonomy Polytypic, with nominate leucorhoa(North Pacific and North Atlantic) of relevancehere.Atlantic Breeds May–September. Immaturenon-breeding visitors depart colonies August orearlier. Numbers build on both sides of theAtlantic in same latitudes as colonies, Sep-tember–October. Thereafter declines in west.Peak numbers in east in October–Novemberapparently greater than total eastern population(assessed through counts during autumn galesand wrecks), thus almost certainly includingbirds from northwest Atlantic populations.Widely dispersed across tropical and subtrop-ical Atlantic, October–March, return passageMarch–May. First arrivals on British breedinggrounds late April. Immature non-breeders’return to colonies is more leisurely, othersremain in tropical zones during breedingseason. Leach’s regularly prospects and even

nests in small numbers in southern oceans(Imber & Lovegrove 1982; Randall & Randall1986).Jizz Like a Common Nighthawk Chordeilesminor.Size Body length 202 mm. Wingspan 462 mm.Small size differences between subspecies(Ainley 1980; Brooke 2004), although Post(1998) found notable differences from pub-lished data when measuring 35 birds wreckedoff Portugal, December 1996/January 1997.Structure Wing shape P9 longest; P10 5–12; P81–5; P7 9–15; P6 20–28; P1 76–92 mm shorter.When travelling, wings long and quite narrow,decidedly pointed wing-tips, both leading andtrailing edges strongly angular and wings oftenswept back. Head-on travelling profile Wingsslightly bowed, forming shallow-M, armsmedium length, hands long. Tail shape Mediumlength, deeply forked and scooped; longest tailfeathers as long as primaries when sat on sea



170. Wilson’s Storm-petrel Oceanites oceanicus, South Georgia, March 2006.This Wilson’s is feeding and hence itswings appear paddle-shaped, its tail is fanned, and the long spindly legs are dangling down. Note how the light iscatching the right underwing-coverts creating the effect of a bronze flush; the left upperwing-coverts and covertbar are hidden by the right wing, so only the brown-black left upperwing primary coverts show. In addition, the

yellow webbings of the left foot are visible in this image.

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(Sibley 2000), but can be difficult to see at dis-tance, especially when angle of view is shallow.Lightly forked when fanned. Toe projectionNone. Body build Rather long, slim body. Billshape and proportions At sea looks relativelylong and slender. Close up, long and slenderlook substantiated; slightly hooked, with nasaltubes 40% bill length.Plumage General colour and colour tones Cool-toned black-brown, but bleaches browner withage. Close up, browner below, pale ashy-brownon chin and forehead, with strong grey- orslate-blue tinge on upperparts and chest infresh plumage (ashy, grey and slate-blue ele-ments contribute to cool tone). Juvenile haspale edges to body feathers that wear offquickly. Upperwing-covert bars Striking,stretching from leading edge to body, formed bycool brown-grey greater coverts, plus somemedian and lesser coverts on outermost of bars,hence bars broaden towards and reach leadingedge, giving a teardrop shape on each wing.Covert bars become paler with age though maybecome narrower through feather wear. Under-wing-covert and axillary panels Evenly black-brown. White on rump, tail-coverts and rearflanks Uppertail-coverts white, some irregularlytipped black-brown, although central feathersoften all-dark forming diagnostic ‘grey-divide’down centre of roughly rectangular whiterump, which, from above, makes the white



171. Leach’s Storm-petrel Oceanodroma leucorhoa,equatorial Atlantic 0°00.000’S, 17°33.462’W, April

2006.The white patch of the rump, tail-coverts andrear flanks is normally roughly rectangular, is longer

than it is broad, and has a diagnostic ‘grey-divide’down the centre which, from above, makes the white

patch V-shaped. Rarely, as shown here, white isrestricted to sides of rump, thus erasing the bottomof the V-shape, making residual white quite difficult to

see and the bird look superficially like a Swinhoe’sStorm-petrel O. monorhis. In this case, the possibility

of misidentification was accentuated by the dullupperwing-covert bars, more typical of Swinhoe’sthan Leach’s; in fact, this bird was initially called as a Swinhoe’s! However, in addition to flight jizz that

was typically Leach’s, the following pointers areimportant: the bird is holding its wings swept back,whereas Swinhoe’s holds its wings further forwards

(more like Madeiran); and the tail has a relativelydeep fork, is scooped and looks ragged, whereas thefork in Swinhoe’s is considerably shallower, more likea notch, and is mostly closed, similar to the side-on

profile of a long-tailed swift (Apodidae).

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172. Leach’s Storm-petrels Oceanodroma leucorhoa, equatorial Atlantic 0°00.000’S, 17°33.462’W, April 2006.All classic structural and plumage features of Leach’s are captured in this image (see text).

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patch V-shaped. White patch islonger than it is broad; dull whiterather than gleaming white; and,rarely, is restricted to sides of rump,thus erasing bottom of V-shape(when white very restricted in thisarea, looks superficially likeSwinhoe’s Storm-petrel Ocean-odroma monorhis; see plate p. 81 inBlomdahl et al. 2003). White patchbarely extends to rear flanks orlateral undertail-coverts. Thus,white hard to see in flight, beingeasier when close up, especiallygiven a deep angle of view. Likewise,white barely visible when sat on sea(Sibley 2000). White on belly None.Flight behaviour Keeps mainlywithin 5 m of sea surface. TravellingBuoyant and graceful involvingdeep, elastic, languid wingbeats withfrequent long shearing glides onslightly bowed wings. Overall courseirregular, punctuated with unpre-

dictable speedand/or directionchanges, involvingdarting, verticalleaping, andbounding ahead. Instrong wind,employs highlyerratic flight,including shearing,zigzagging, andbounding throughwave troughs. Whenshearing, likened toPuffinus shearwatersand in buoyantflight likened toSterna terns (BWPi2006); flight alsolikened to that ofS o f t - p l u m a g e dPetrel Pterodromamollis (Veit et al.1996). That said, amigrant observed inFebruary from aheadland in Scilly,heading into strongwesterly winds,attempted to



173. Leach’s Storm-petrel Oceanodroma leucorhoa, equatorialAtlantic 0°00.000’S, 17°33.462’W,April 2006. In travelling flight,

the overall course of a Leach’s is irregular, punctuated withunpredictable speed and/or direction changes, involving darting,vertical leaping, and bounding ahead.The Leach’s in this image

is making a sudden direction change.

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174. Leach’s Storm-petrel Oceanodroma leucorhoa (left) with Wilson’s Storm-petrelOceanites oceanicus (right), equatorial Atlantic 0°00.000’S, 17°33.462’W, April 2006.The photographer estimated that the Wilson’s is about 0.25 m behind the Leach’s,but with optical effects taken into account the two storm-petrels are roughly to

scale, as if on the same plane. Note how stiff the Wilson’s wings appear compared with the flexible look of the Leach’s wings, even in this still image. Note also how

the Leach’s legs and toes fall short of the tail-tip compared with the Wilson’s,which has a noticeable toe projection. In addition,Wilson’s seems to have a

relatively long rear carriage compared to Leach’s.

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progress directly into windwith languid wingbeats foreight minutes, then ‘con-ceded’ by turning 90° leftand sheared, briefly turnedinto the wind, again turned90° left and sheared,repeating this behaviourthree times, then lost tosight. In so doing it eventu-ally progressed relativelyquickly in a direction 90°left of the oncoming wind.In similar conditions, Euro-pean Storm-petrel madesurprisingly good headwayinto wind. Feeding Swoopsover and around food source such as an oilyslick. When food item located, tends to hang orhover over it facing into wind, sometimes foot-pattering, with wings raised over back normallya flattened V-shape, though angle ostensiblydetermined by wind strength, wings paddle-shaped, and dips head to surface seize. In hov-ering flight, likened to Larus gull (BWPi 2006),presumably in the way Larus gulls hover andpick over food items in wave surf, rising up anddropping back down in synchrony with eachwave. In light winds may sit on sea picking foodfrom surface like Fulmar Fulmarus glacialis.Leach’s observed at Cheddar Reservoir, Som-erset, in November 1970 fed with wings heldslightly raised and almost motionless while, atsame time, short legs dangled, with feet occa-sionally pattering on water surface (Rabbitts1979). However, a bird observed at NewBrighton, Cheshire & Wirral, in September1978, fed over marine swimming pool, pickingfood from water surface, short legs danglingand feet pattering or walking on water surface(Page & Greaves 1979). Contra Blomdahl et al.(2003), Leach’s follows vessels at least occasion-ally (pers. obs. in central-east Atlantic, March2006; also see Atkin 1979). Probably associateswith cetaceans.Overall impression Medium-sized, slender,cool-toned black-brown, bold upperwing-covert bars, in flight buoyant, versatile andunpredictable.

Madeiran Storm-petrelTaxonomy Considered monotypic, thoughprobably polytypic given recent discovery oftwo distinct populations (‘hot season’ and ‘cool

season’) in the Azores, each with non-overlap-ping breeding and dispersal periods, and whichlack vocal recognition of the other (Bolton2007). Ecological counterpart of Leach’s Storm-petrel in tropical and adjoining sectors inwarm, deep pelagic waters.Atlantic Breeds Northeast Atlantic, Berlengasand Farilhões off Portugal, Desertas and Sal-vages off Madeira, Canary Islands, Cape VerdeIslands and Azores; in the southeastern Atlantic,breeds Ascension and islets off St Helena.Uncertain whether birds disperse or undertakesystematic migration after breeding (Brooke2004). Madeiran Storm-petrels certainly movewestwards and are seen regularly on pelagictrips off eastern seaboard of USA, most notablyoff North Carolina (see www.patteson.com).Apparently does not move northwards towestern Europe, where it is an extreme vagrant(except Portugal; see Appendix 4), even thoughconsiderably closer to breeding grounds thaneastern seaboard of USA. Seemingly coupled towarm deep pelagic waters in the Atlantic.Jizz Like a European Nightjar Caprimulguseuropaeus.Size Body length 200 mm. Wingspan 448 mm.On Azores, weight of ‘hot season’ populationnotably lower than that of ‘cool season’ popula-tion, while populations from Azores larger thanbreeders on Salvages (Brooke 2004).Structure Wing shape Formula, P9 longest; P105–9; P8 1–4; P7 8–13; P6 18–26; P1 88–96 mmshorter. When travelling, wings long with broadarms, blunt-ended wing-tips, and wings nor-mally held straight out rather then swept back,thus leading and trailing edges only moderatelyangular. Head-on travelling profile Wings



175. Leach’s Storm-petrel Oceanodroma leucorhoa (left) and Madeiran Storm-petrel O. castro (right), heads and bills, roughly to scale. Note

that the bill of Leach’s is long, slender and slightly hooked, whereas that of Madeiran is surprisingly bulky and heavily hooked for a storm-petrel.

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slightly bowed yielding shallow-M, armsmedium length, hands long. Tail shape Shallowfork with outermost feather 4–12 mm longerthan central feathers; appears square-endedwhen fanned. Toe projection None. Body buildLength of body as Leach’s, but because ofgreater girth has decidedly chunky look. Billshape and proportions At sea looks bulky for astorm-petrel. Close up, surprisingly bulky andquite heavily hooked, with nasal tubes 40% billlength.Plumage General colour and colour tones In freshplumage, warm black-brown, but bleachesbrowner with age. Close up, browner below,with blue-grey tinge from hind-crown to back,sides of head, and chest. Overall rather plain-looking. Upperwing-covert bars At range, almostuniformly dark upperwings, with covert barsbarely discernible in some conditions. Close up,greater coverts form dull bars, a little moreobvious when bleached, but never shows broadpale covert bars and these do not reach theleading edge like Leach’s. At close to mediumrange, pale pencil line along tips of greatercoverts (outer webs fringed pale), but these

wear off quickly. Underwing-covert and axillarypanels Evenly hued black-brown. White onrump, tail-coverts and rear flanks Narrow rec-tangular white patch, broader than it is long(hence North American name ‘Band-rumpedStorm-petrel’), which, from above, looksslightly U-shaped. ‘Band rump’ formed by whiteuppertail-coverts, longer ones tipped black,forming conspicuous, even band across base oftail. White extends to lateral undertail-covertsand rear flanks. In flight, white seeminglyalways in view whatever the angle of observa-tion; also visible when sat on sea (Sibley 2000).White on belly None.Flight behaviour Keeps mainly within 5 m ofsea surface. Travelling Fairly steady andbuoyant, progressing with runs of six or soshallow wingbeats, sometimes with low bankingturns, sometimes with short Puffinus-shear-water-like glides on wings slightly bowed justbelow horizontal. Gliding sometimes prolongedgiven sufficient supporting breeze. Often pro-gresses by weaving a regular horizontal zigzag,banking left and proceeding for a while, thenbanking right and proceeding, etc. Feeding Will



176. Madeiran Storm-petrel Oceanodroma castro, off St Helena,April 2006.All the classic structural and plumagefeatures of Madeiran are captured in this image (see text).

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foot-patter and walk with feet on sea surface,with wings raised over back, normally in a flat-tened V-shape, angle ostensibly determined bywind strength, wings paddle-shaped; butemploys this feeding strategy least commonly ofthe four regular North Atlantic storm-petrelsand is least accomplished at it (Blomdahl et al.2003; BWPi 2006; pers. obs.). In the main,steadily and systematically explores food source,employing even flight intermixed with periodsof gliding, rising 1–2 m with regular shallowwingbeats, then gliding back to sea surface as iffollowing a gentle undulating contour. Maydouble-back on itself, gaining height moresteeply, circling up to 3–4 m above sea surface,presumably in search of prey, at which timeflight a little more erratic, perhaps hinting atLeach’s. However, does not leap and bound, orswitch direction and speed like Leach’s.Descends and seizes food items from seasurface. In light winds may sit on sea surfacepicking at food as Fulmar. Regularly dives; off StHelena timed at one or two seconds (fromvideo). Off Azores, Bried (2005) showed thataverage maximum dive was 0.85 m and thatdiving was part of typical foraging behaviour.Opinion varies as to propensity of Madeirans tofollow vessels, though near St Helena followedMV Professor Molchanov as well as readily asso-

ciating with small local fishing vessels (pers.obs.; also see Brown 1980). Probably associateswith cetaceans.Overall impression Medium-sized, chunky-bodied and heavy-billed, warm-toned black-brown, in flight methodical and predictable, butoverall rather plain.

Black-bellied Storm-petrelTaxonomy Polytypic, F. t. tropica (Auckland andAntipodes Islands, Kerguelen, Crozets andPrince Edward Islands, islands of Scotia Sea),F. t. melanoleuca (Gough Island); but seeAppendix 5.Atlantic Breeds mainly south of Antarctic PolarFront with main breeding October–April.Northwards movement from coloniesApril–May. Disperses northwards into tropicaland subtropical seas to 10ºN in Atlantic,May–October. Southward movement September–October with first returns variablebetween locations, roughly September–November. Little information on range ofjuveniles and immatures.Jizz No obvious avian simile, but like an exhibi-tion skateboarder skilfully traversing ever-changing sea contours and flipping betweentroughs.Size Body length 200 mm. Wingspan 455 mm.



177. Madeiran Storm-petrel Oceanodroma castro, off St Helena,April 2006. Madeiran appears strangely reluctantto hang or hover over food items, foot-patter or surface-seize. Consequently, it employs this feeding strategy theleast of the six storm-petrels’ featuring in this paper.As in this image, Madeiran appears rather clumsy, especially if

compared with the accomplished-looking Wilson’s in plate 005.

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Geographical variation not obvious (Brooke2004) or minimal (Stephenson et al. 2007b).Structure Wing shape P9 longest; P10 8–11; P81–3; P7 11–16; P6 22–27; P1 81–86 mm shorter.Primaries pointed in juvenile, rounded inadults. When travelling, wings overall broad,often strongly curved leading edges that taper topointed wing-tips. Trailing edges straight.Head-on travelling profile Slightly bowedyielding shallow-M, arms short and hands long.Tail shape Short, square-ended, slightly roundedwhen fanned. Toe projection Toes projectnotably beyond end of tail, though less so thanWilson’s. Body build Compact and fat. Bill shapeand proportions At sea looks small. Close up,short, broad-based, finely hooked, with nasaltubes 50% bill length.Plumage General colour and colour tones In freshplumage, black-brown head, neck and upper-parts including wing-coverts, with head darkest,but bleaches browner with age. Back and upper-wing darker and warmer-toned brown than onWhite-bellied. Mantle and scapulars with whitefringes (c. 0.5 mm in fresh plumage) lessmarked than White-bellied (c. 2.0 mm in freshplumage) (K. Roselaar pers. comm.). Upper-wing-covert bars Greater coverts grey-browncreating inconspicuous covert bars, a little moreobvious when bleached. Underwing-covert andaxillary panels White across greater and median

underwing-coverts and axillaries, but slightlydirty-looking on outermost greater coverts thatare dark-centred. White panel bordered bybroad blackish leading-edge and blackishremiges. White on rump, tail-coverts and rearflanks Rump black-brown, uppertail-covertswhite extending to underparts, white patchroughly rectangular and from above slightly U-shaped. Amount of white on undertail-covertsvariable; central feathers all-black as a continua-tion of the black belly stripe (K. Roselaar pers.comm.). White on belly Sides of lower breast,abdomen and flanks white, with diagnosticblack-brown central belly stripe, reduced oreven broken on pale birds but which, if com-plete, joins V-shaped centre of black-brownupper-breast with black-brown undertail-coverts, but black-brown to white interfacessmudgy, yielding overall a dirty look. Popula-tion of melanoleuca breeding on Gough Islandhas white belly like White-bellied Storm-petrel,causing identification and taxonomic problems(see Appendix 5). Likewise, populations onsome New Zealand sub-Antarctic islands showbroken and thus incomplete belly stripe, withsome individuals apparently showing no darkstripe or mid-line markings (B. Stephensonpers. comm.).Flight behaviour Flies mostly within 5 m of seasurface, though tends to keep very low. Travel-

ling Glides like smallshearwater, hugs seasurface, up anddown over ever-changing contours,flips betweentroughs. In breezyconditions flapswings infrequentlyin short bursts,more so in calmerconditions. FeedingGlides and skims,hugs ever-changingcontours of seasurface, hopping,skipping andsplashing, swingingfrom one side oftrough to other,bounding from onetrough to another,doubling back,surface-snatching,



178. White-bellied Storm-petrel Fregetta grallaria (probable, see Appendix 5), off Tristan da Cunha group, March 2006.White-bellied, like Black-bellied, glides and skimsclose to ever-changing contours of the sea surface, hopping and skipping (sometimes

splashing) as in this image, whilst opportunistically surface-snatching food items.

Brya

n Th

omas

BB July 2007 5/6/07 13:31 Page 426

also dives. Will foot-patter, albeit briefly.Follows in bow-wash and wake of vessels andprobably associates with cetaceans.Overall impression Medium-sized, fat, compact,pied, vaguely dirty-looking, hugging contoursof sea in flight.

White-bellied Storm-petrelTaxonomy Polytypic: F. g. grallaria (RoachIsland of Lord Howe group, Kermadec Islands),F. g. leucogaster (Tristan da Cunha group, StPaul), F. g. segethi (Juan Fernández Islands), F. g.titan (Rapa of Austral group).Atlantic Little known of non-breeding season,but may disperse widely from subtropical andtemperate breeding sites into tropical and sub-tropical seas south of equator, presumably inAtlantic involving populations from Tristan daCunha group (Marchant & Higgins 1990;Brooke 2004).Jizz As Black-bellied.Size Body length 200 mm. Wingspan 462 mm.Differences in biometrics important for subspe-cific identification, although further studyrequired (Brooke 2004).Structure As Black-bellied except: Wing shapeP9 longest; P10 8–11; P8 0–4; P7 12–15; P624–28; P1 75–90 mm shorter. Toe projectionMost literature states none or makes nomention, but apparently can show marginalprojection (Shirihai 2002). Amount of projec-tion varies geographically, individually, and tosome degree with state of wear and moult(Shirihai pers. comm.).Plumage Polymorphic with light, intermediateand dark morphs (last two from Lord HoweIsland off eastern Australia and not dealt withhere). General colour and colour tones In freshplumage, black-brown head, neck and upper-parts including wing-coverts; head darkest, butbleaches browner with age. Back and upperwingpaler and cooler-toned black-brown than onBlack-bellied. Mantle and scapulars show dis-tinct white fringes (c.2.0 mm in fresh plumage)more marked than on Black-bellied (c. 0.5 mmin fresh plumage) (K. Roselaar pers. comm.),creating scaly effect at close range, but whendistant these fringes appear to merge with black-brown of feathers creating greyer cast. However,fringes wear off with age, so this feature limitedas a means of separation from Black-bellied.Upperwing-covert bars Greater coverts pale grey-brown creating fairly obvious covert bars, cer-tainly more conspicuous than those of

Black-bellied; these become paler when bleachedbut may become less prominent as featherswear. Underwing-covert and axillary panels AsBlack-bellied. White on rump, tail-coverts andrear flanks As Black-bellied except: Centralundertail-coverts black-brown with narrowwhite tips, lateral undertail-coverts white withdark brown subterminal band (Marchant &Higgins 1990). Undertail-coverts depictedwholly white in Shirihai (2002). White on bellyLower breast, abdomen and flanks white, gener-ally looking clean, having straight, sharp andneat interface with black-brown upper breastand undertail-coverts (also see Appendix 5).Flight behaviour As Black-bellied, but perhapsmore varied and erratic, including more glides(Shirihai 2002).Overall impression Medium-sized, fat, compact,pied, clean-looking, hugging contours of sea inflight.

Acknowledgments

Thanks to Ashley Fisher for critical feedback on an earlierdraft and for the idea of setting stills of several specieswithin a single plate; to Hadoram Shirihai for criticalfeedback on an earlier draft and for allowing us to use animportant digital still from his keenly awaited Albatrosses,Petrels and Shearwaters of the World to be published byA&C Black, London; and to Kees Roselaar and BrentStephenson for critical feedback on an earlier draft anddiscussion of taxonomy of Fregetta storm-petrels of theTristan da Cunha group. For assistance with vagrantMadeiran Storm-petrel records in Europe, we are gratefulto Marc Duquet and Jean-Yves Fremont (Secretary) andthe French Rarities Committee (Comite d’HomologationNational), Peter Fraser (Secretary) and the British BirdsRarities Committee, Paul Milne (Secretary) and the IrishRare Birds Committee, Ricard Gutiérrez (Joint SecretaryCR-SEO/BirdLife) and Antero Topp. For assistance withvagrant Nor th Atlantic Fregetta records, John Brodie-Good, Dominic Mitchell, and Angus Wilson providedvaluable information, while Steve Gantlett, Mor tenJørgensen, Tony Marr, Viv Stratton, and Will Wagstaff alsoprovided useful general inputs. Ren Hathway prepared fig.2 from a sketch by Robert Flood. Our very special thanksgo to Alec Hicks and Joe Pender, respectively skippers ofMV Kingfisher and MV Sapphire, for making it possible forus to go to sea off Scilly over 300 times from 2000 to2006, facilitating extensive vessel-based observations ofEuropean, Leach’s, and Wilson’s Storm-petrels, plusinvaluable opportunities to photograph them.

References

Ainley, D. G. 1980. Geographic variation in Leach’s Storm-petrel. Auk 97: 837–853.

Anon. 1951. Madeiran Storm-petrel Oceanodroma castro,Huelva, November 1951. Ardeola 1: 128.

— 1970. Madeiran Storm-petrel Oceanodroma castro,Badajoz, February 1970. Ardeola 15: 101.

— 1982. Madeiran Storm-petrel Oceanodroma castro,Huelva, January 1982. Ardeola 29: 177.

Atkin, K. 1979. Flight characters of Leach’s Petrel. Brit. Birds72: 334–335.



BB July 2007 5/6/07 13:31 Page 427



Tabl

e 3.

Sum

mar

y ta

ble

of id

entif

icat

ion

feat

ures

for

Euro

pean

Sto

rm-p

etre

l Hyd

roba

tes

pela

gicu

s,W

ilson

’s St

orm

-pet

rel O

cean

ites

ocea

nicu

s,Le

ach’

s St

orm

-pet

rel O

cean

odro

ma

leuc

orho

a,M

adei

ran

Stor

m-p

etre

l O.c

astro

,Bla

ck-b

ellie

d St

orm

-pet

rel F

rege

tta tr

opica

and

Whi

te-b

ellie

d St

orm

-pet

rel F

.gra

llaria

.The

mai

n id

entif

icat

ion

feat

ures

of t

he s

ix s

peci

es h

ave

been

ext

ract

ed fr

om t

he p

rece

ding

spe

cies

acc

ount

s.

Spec

ies

Euro

pean

Wils

on’s

Leac

h’s

Mad

eira

nB

lack

-bel

lied

Wh

ite-

belli

ed

Smal

lSm

all–

med

ium

Med

ium

Med

ium

Med

ium

Med

ium

Size

Com

pact

,dar

k,bu

sy a

nd

seem

ingl

y re

stle

ss;f

lash

esw

hit

e on

un

derw

ings

infl

igh

t (l

ess

so w

hen

wor

n)

Even

ly p

ropo

rtio

ned

,w

arm

-ton

ed b

lack

-bro

wn

wit

h o

bvio

us

upp

erw

ing-

cove

rt b

ars;

acco

mpl

ish

edfl

igh

t,es

peci

ally

wh

enfe

edin

g

Slen

der,

cool

-ton

ed b

lack

-br

own

,bol

d u

pper

win

g-co

vert

bar

s;in

flig

ht

buoy

ant,

vers

atile

an

du

npr

edic

tabl

e

Chu

nky

-bod

ied

and

hea

vy-b

illed

,war

m-t

oned

blac

k-br

own

;in

flig

ht

met

hod

ical

an

d pr

e-di

ctab

le,o

vera

ll ra

ther

plai

n

Fat,

com

pact

,pie

d,va

guel

y di

rty-

look

ing;

hugs

con

tou

rs o

fse

a in

flig

ht

Fat,

com

pact

,pie

d,cl

ean

-lo

okin

g;hu

gs c

onto

urs

of

sea

in fl

igh

t

Ove

rall

impr

essi

on

Smal

l bat

Bar

n S

wal

low

Com

mon

Nig

hth

awk

Eu

rope

an N

igh

tjar

Exh

ibit

ion

ska

tebo

arde

rA

s B

lack

-bel

lied

Sim

ile

Bas

elin

e sp

ecie

s,1.

00 &

1.00

1.05

& 1

.08,

but

appe

ars

up

to 1

.5 t

imes

as

big

1.21

& 1

.28,

but

appe

ars

up

to t

wic

e as

big

1.17

& 1

.27,

pres

um

ably

wou

ld a

ppea

r as

big

as

Leac

h’s

1.19

& 1

.27,

pres

um

ably

wou

ld a

ppea

r as

big

as

Leac

h’s,

thou

gh fa

tter

1.21

& 1

.27,

pres

um

ably

wou

ld a

ppea

r as

big

as

Leac

h’s,

thou

gh fa

tter

Rel

ativ

ew

ings

pan

,bo

dy le

ngt

h

Shor

t &

bro

ad w

ith

win

g-ti

ps b

lun

t-en

ded;

both

lead

ing

& t

raili

ng

edge

sst

ron

gly

angu

lar

Med

ium

len

gth

,bro

ad,

poin

ted

win

g-ti

ps;

lead

ing

edge

sm

ooth

lycu

rved

,tra

ilin

g ed

gest

raig

ht

Lon

g &

qu

ite

nar

row

,de

cide

dly

poin

ted

win

g-ti

ps;l

eadi

ng

& t

raili

ng

edge

s st

ron

gly

angu

lar,

win

gs o

ften

sw

ept

back

Lon

g,br

oad

arm

s,bl

un

t-en

ded

win

g-ti

ps,n

or-

mal

ly h

eld

stra

igh

t ou

t so

lead

ing

& t

raili

ng

edge

son

ly m

oder

atel

y an

gula

r

Bro

ad w

ith

sh

ort

arm

s,st

ron

gly

curv

ed le

adin

g &

str

aigh

t tr

ailin

g ed

ges,

tape

rs to

poi

nte

d w

ing-

tips

As

Bla

ck-b

ellie

dW

ing

shap

ew

hen

tr

avel

ling

Win

gs s

ligh

tly

bow

edfo

rmin

g sh

allo

w-M

,arm

s&

han

ds q

uit

e sh

ort

Win

gs s

trai

ght

& s

tiff

,ar

ms

shor

t,h

ands

med

ium

len

gth

Slig

htl

y bo

wed

insh

allo

w-M

,arm

s m

ediu

mle

ngt

h,h

ands

lon

g

Slig

htl

y bo

wed

insh

allo

w-M

,arm

s m

ediu

mle

ngt

h,h

ands

lon

g

Slig

htl

y bo

wed

insh

allo

w-M

,arm

s sh

ort,

han

ds lo

ng

As

Bla

ck-b

ellie

dTr

avel

ling

head

-on

win

gpr

ofile

Shor

t,ca

n lo

ok s

quar

e,th

ough

gen

tly

rou

nde

d;cl

earl

y ro

un

ded

wh

enfa

nn

ed

Slig

htl

y co

nca

ve,c

orn

ers

rou

nde

d;ta

il sl

igh

tly

rou

nde

d w

hen

fan

ned

Dee

ply

fork

ed &

sco

oped

;lig

htl

y fo

rked

wh

enfa

nn

ed

Shal

low

fork

;app

ears

squ

are-

ende

d w

hen

fan

ned

Shor

t,sq

uar

e-en

ded;

slig

htl

y ro

un

ded

wh

enfa

nn

ed

As

Bla

ck-b

ellie

dTa

il sh

ape

Non

eO

bvio

us,

but

rare

lyre

trac

ts le

gsN

one

Non

eO

bvio

us,

but

rare

lyre

trac

ts le

gsA

ppar

entl

y sl

igh

t,bu

tra

rely

ret

ract

s le

gsTo

e pr

ojec

tion

Com

pact

wit

h s

hor

t bo

dyEv

en p

ropo

rtio

ns

inle

ngt

h &

gir

th,l

ong

rear

carr

iage

Rat

her

lon

g,sl

im b

ody

Dec

ided

ly c

hun

kyC

ompa

ct &

fat

As

Bla

ck-b

ellie

dB

ody

build

BB July 2007 5/6/07 13:31 Page 428



Spec

ies

Euro

pean

Wils

on’s

Leac

h’s

Mad

eira

nB

lack

-bel

lied

Wh

ite-

belli

edSh

ort,

len

gth

& d

epth

inpr

opor

tion

,slig

htl

yde

curv

ed &

hoo

ked

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ium

len

gth

,bro

ad-

base

d,sl

igh

tly

hoo

ked

Rel

ativ

ely

lon

g &

sle

nde

r,sl

igh

tly

hoo

ked

Bu

lky

and

quit

e h

eavi

lyh

ooke

d fo

r st

orm

-pet

rel

Shor

t,br

oad-

base

d,fi

nel

yh

ooke

dA

s B

lack

-bel

lied

Bill

sh

ape

and

prop

orti

ons

Dar

kest

of

six,

soot

y-br

own

,ble

ach

es b

row

ner

wit

h a

ge

War

m-t

oned

bla

ck-

brow

n,b

leac

hes

bro

wn

erw

ith

age

Coo

l-to

ned

bla

ck-b

row

n,

blea

ches

bro

wn

er w

ith

age

War

m-t

oned

bla

ck-

brow

n,b

leac

hes

bro

wn

erw

ith

age

;ove

rall,

rath

erpl

ain

-loo

kin

g

Bla

ck-b

row

n,b

leac

hes

brow

n w

ith

age

;man

tle

&sc

apu

lars

hav

e in

dist

inct

nar

row

wh

ite

frin

ges

that

wea

r of

fw

ith

age

;bac

k &

upp

erw

ing

dark

er a

nd

war

mer

ton

ed t

han

on

Wh

ite-

belli

ed

Bla

ck-b

row

n,b

leac

hes

brow

n w

ith

age

;man

tle

&sc

apu

lars

hav

e di

stin

ctn

arro

w w

hit

e fr

inge

s th

atw

ear

off

wit

h a

ge,t

hus

this

feat

ure

lim

ited

as

mea

ns

ofdi

stin

ctio

n fr

omB

lack

-bel

lied

Gen

eral

colo

ur

and

colo

ur

ton

es

At

ran

ge,u

nif

orm

dar

ku

pper

win

g;cl

ose

up,

grea

ter

cove

rts

form

ver

ydu

ll ba

rs,m

argi

nal

lym

ore

not

icea

ble

wh

enbl

each

ed,w

ith

pal

e pe

nci

llin

e al

ong

tips

th

atbe

com

es n

arro

wer

wit

hfe

ath

er w

ear

Obv

iou

s &

bro

ad,s

tart

shor

t of

lead

ing

edge

an

dex

ten

d to

bod

y,br

own

-gr

ey to

silv

ery

grea

ter

&du

ller

med

ian

cov

erts

;th

ese

pale

r w

hen

ble

ach

edth

ough

may

bec

ome

nar

-ro

wer

wit

h fe

ath

er w

ear

Stri

kin

g,fr

om le

adin

ged

ge to

bod

y,co

ol b

row

n-

grey

gre

ater

cov

erts

,plu

sou

term

ost

med

ian

&le

sser

cov

erts

,hen

ce b

ars

broa

den

tow

ards

& r

each

lead

ing

edge

,giv

ing

tear

drop

sh

ape;

mu

chm

ore

obvi

ous

than

Mad

eira

n;b

ars

pale

rw

hen

ble

ach

ed t

hou

ghm

ay b

ecom

e n

arro

wer

wit

h fe

ath

er w

ear

At

ran

ge,a

lmos

t u

nif

orm

dark

upp

erw

ings

wit

hco

vert

bar

s ba

rely

dis

-ce

rnib

le;c

lose

-up,

grea

ter

cove

rts

form

du

ll ba

rs,a

littl

e m

ore

obvi

ous

wh

enbl

each

ed,b

ut

nev

er s

how

sbr

oad

pale

cov

ert

bars

Gre

ater

cov

erts

gre

y-br

own

cre

atin

g in

con

spic

-u

ous

cove

rt b

ars,

a lit

tle

mor

e ob

viou

s w

hen

blea

ched

Gre

ater

cov

erts

pal

e gr

ey-

brow

n c

reat

ing

fair

lyob

viou

s co

vert

bar

s,pa

ler

wh

en b

leac

hed

th

ough

may

bec

ome

nar

row

er a

sfe

ath

ers

wea

r;al

way

sm

ore

con

spic

uou

s th

anB

lack

-bel

lied

Upp

er-

win

g-co

vert

ba

rs

In fr

esh

plu

mag

e ey

e-ca

tch

ing

wh

ite

pan

els,

even

at

lon

g ra

nge

;les

sob

viou

s in

wor

n p

lum

age

Even

ly h

ued

soo

ty-b

row

n,

som

e sh

ow b

ron

ze fl

ush

,ra

rely

a p

ale

pan

el

Even

ly h

ued

bla

ck-b

row

nEv

enly

hu

ed b

lack

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wn

Obv

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s w

hit

e pa

nel

,so

me

oute

r gr

eate

r u

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r-w

ing-

cove

rts

dark

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ed w

ith

wh

ite

frin

ges

As

Bla

ck-b

ellie

dU

nde

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g-co

vert

&ax

illar

ypa

nel

s

Bol

d,ro

ugh

ly r

ecta

ngu

lar,

from

abo

ve s

ligh

tly

U-s

hap

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xten

ds to

late

ral u

nde

rtai

l-co

vert

s&

rea

r fl

anks

,see

min

gly

alw

ays

visi

ble

at s

ea

Bol

d,ro

ugh

ly r

ecta

ngu

lar,

from

abo

ve s

ligh

tly

U-s

hap

ed,e

xten

ds to

late

ral u

nde

rtai

l-co

vert

s&

rea

r fl

anks

,see

min

gly

alw

ays

visi

ble

at s

ea

Dul

l & n

ot g

leam

ing

whi

te,

bare

ly e

xten

ds to

und

erta

il-co

vert

s &

rea

r fla

nks,

long

erth

an it

is b

road

,fro

m a

bove

V-s

hape

d,ha

rd to

obs

erve

at s

ea;r

arel

y,w

hite

pat

chre

stri

cted

to r

ump-

side

ser

asin

g bo

ttom

ofV

-sha

pe

Nar

row

,rec

tan

gula

r,br

oade

r th

an it

is lo

ng,

from

abo

ve s

ligh

tly

U-

shap

ed,e

xten

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BB July 2007 5/6/07 13:31 Page 430

Blomdahl,A., Breife, B., & Holmström, N. 2003. FlightIdentification of European Seabirds. Christopher Helm,London.

Bolton, M. 2007. Playback experiments indicate absence ofvocal recognition among temporally and geographicallyseparated populations of Madeiran Storm-petrelsOceanodroma castro. Ibis 149: 255–263.

Boswall, J. 1979. Flight characteristics of Wilson’s Petrel. Brit.Birds, 72: 330–334, 386.

BOU. 1971. The Status of Birds in Britain and Ireland.Blackwell, Oxford.

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Bradshaw, C. 2002. From the Rarities Committee’s files:Rare seabirds and a record of Herald Petrel. Brit. Birds95: 156–65.

Brereton,T. M.,Weir, C., Hobbs, M., & Williams,A. D. 2003.A low-cost, year-round seabird monitoring programmein the English Channel and Bay of Biscay: preliminaryresults 1995–2001. Ornis Hungarica 12/13: 105–113.

Bried, J. 2005. Diving ability of the Madeiran Storm-petrel.Waterbirds 28: 162–166.

Hume, R.A., Harrison, P.,Wallis, H.W., Cutting, K.,Young,S.A., Charles, P., England,T. M., & Ward, J. R. 1997. Fromthe Rarities Committee’s files: ‘The Chalice petrel’. Brit.Birds 90: 305–313.

Brooke, M. 2004. Albatrosses and Petrels across the World.OUP, Oxford.

Brown, R. G. B. 1980. Flight characteristics of MadeiranPetrel. Brit. Birds 73: 263–264.

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Cagnon, C., Lauga, B., Hemery, G., & Mouches, C. 2004.Phylogenetic differentiation of storm-petrels(Hydrobates pelagicus) based on cytochrome bmitochondrial DNA variation. Marine Biology 145:1257–1264.

Clarke,T. 2006. Birds of the Atlantic Islands. ChristopherHelm, London.

Costas, R., Gutiérrez, R., Exposito, C., & Taibo, C. R. 1996.Painõ de Madeira Oceanodroma castro. In: De Juana, E.y el comité ibérico de rarezas de la SEO,Observaciones homologadas de aves raras en Espana yPortugal. Informe de 1994. Ardeola 43: 106.

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Dubois, P. J., Le Marechal, P., Olioso, G., & Yésou, P. 2001.Inventaire des Oiseaux de France.Avifaune de la Francemétropolitaine. Nathan, Paris.

Dunne, P. 2006. Pete Dunne’s Essential Field GuideCompanion. Houghton Mifflin, Boston, MA.

Enticott, J., & Tipling, D. 1997. Photographic Handbook of theSeabirds of the World. New Holland, London.

Flood, R. L. 2003.The New Zealand Storm-petrel is notextinct. Birding World 16: 479–482.

— & Fisher, E.A. 2005.Wilson’s Petrels off the Isles ofScilly: a five-year analysis, 2000–2004. Birding World 18:247–249.

—, Saville, S., Southey, I., Stephenson, B., & Thomas, B. 2004.Digital resurrection of the New Zealand Storm-petrel.Southern Bird 17: 6.

Force, M. 1997. Comments on ‘The Chalice petrel’. Brit.Birds 90: 339–342.

Friesen,V. L., Lodha,V., Monteiro, L. R., & Furness, R.W.1998. Evidence for sympatric speciation in the Band-rumped Storm-petrel Oceanodroma castro. Ostrich 69:400–401.

Garner, M., & Mullarney, K. 2004.A critical look at theevidence relating to ‘the Chalice petrel’. Brit. Birds 97:336–345.

Griffiths,A. M. 1981. European Storm-petrels Hydrobatespelagicus feeding by diving off South Africa. Cormorant 9:47.

Guris, P.A., Overton, M. D.,Tove, M. H., & Wiltraut, R. 2004.First North American record of Black-bellied Storm-petrel (Fregetta tropica). North American Birds 58:618–621.

Haase, B. J. M. 1988.A sight-record of a White-belliedStorm-petrel Fregetta grallaria in the Western Palearctic.Ardea 76: 210.

Haney, J. C. 1985. Band-rumped Storm-petrel occurrencesin relation to upwelling off the coast of the south-eastern United States. Wilson Bull. 97: 543–547.

Harrison, P. 1983a. Seabirds: an identification guide. CroomHelm, London.

— 1983b. Identification of white-rumped North Atlanticpetrels. Brit. Birds 76: 161–174.

— 1987. Seabirds of the World: a photographic guide. Helm,London.

Imber, M. J., & Lovegrove,T. G. 1982. Leach’s Storm-petrels(Oceanodroma leucorhoa) prospecting for nest sites onthe Chatham Islands. Notornis 29: 101–108.

Juppinen, P., & Collanus, N. 1994. MadeirankeijuOceanodroma castro Suonenjoki, Iisvesi. Linnut 6: 9–19.

Kennedy, P. G., Ruttledge, R. F., & Scroope, G. F. 1954. Birdsof Ireland. Oliver & Boyd, Edinburgh.

Koppejan,T. 2001. Painõ de Madeira Oceanodroma castro.In: De Juana, E. y el comité de rarezas de la SEO,Observaciones de aves raras en Espana.Anno 1999.Ardeola 48: 119–120.

Lalanne,Y., Hérnery, G., Cagnon, C., D’Arnico, F., D’Elbée, J.,& Mouchès, C. 2001. Discrimination morphologique dessous-espèces d’océanite tempête: nouveaux résultatspour deux populations Mediterranéennes. Alauda 69:475–482.

Marchant, S., & Higgins, P. J. (co-ordinators). 1990. Handbookof Australian, New Zealand and Antarctic Birds.Vol. 1.OUP, Melbourne.

Marsh, P. 1980. Identification problem produced by Leach’sPetrel in moult. Brit. Birds 73: 474.

Maumary, L., & Baudraz, M. 2000. Oiseaux rares etobservations inhabituelles en Suisse en 1999.9e rapport de la Commission de l’avifaune Suisse.Nos Oiseaux 47: 239–258.

Monteiro, L. R., & Furness, R.W. 1998. Speciation throughtemporal segregation of Madeiran Storm-petrel(Oceanodroma castro) populations in the Azores? Phil.Trans. R. Soc. London B 353: 945–953.

Murphy, R. S. 1915.The Atlantic range of Leach’s Petrel(Oceanodroma leucorhoa (Vieillot)). Auk 32: 170–173.

Naveen, R. 1981–82. Storm-petrels of the World: anintroductory guide to their identification. Birding 13:216–239; 14: 10–15, 56–62, 140–47.

Onley, D., & Scofield, P. 2007. Albatrosses, Petrels andShearwaters of the World. Christopher Helm, London.

Page, D., & Greaves, P. 1979. Leach’s Petrels foot-patteringon water. Brit. Birds 72: 334.

Penhallurick, R. D. 1978. The Birds of Cornwall and the Islesof Scilly. Headland Publications, Ruthin.

Post, J. N. J. 1998. Biometrics of 35 specimens of theLeach’s Storm-petrel Oceanodroma leucorhoa from awreck in southern Portugal. Deinsea 4: 77–89.

Rabbitts, B. 1979. Leach’s Petrels foot-pattering on water.Brit. Birds 72: 334.

Randall, R. M. & Randall, B. M. 1986.The seasonaloccurrence of Leach’s Storm-petrel Oceanodromaleucorhoa at St. Croix Island, South Africa. Ostrich 57:157–161.

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Sangster, G. 1999.Trends in systematics: cryptic species ofstorm-petrels in the Azores? Dutch Birding 21: 101–106.

Saville, S., Stephenson, B., & Southey, I. 2003.A possiblesighting of an ‘extinct’ bird – the New Zealand Storm-petrel. Birding World 16: 173–175.

Shirihai, H. 2002. The Complete Guide to Antarctic Wildlife.Alula Press, Espoo, Finland.

— In prep. Albatrosses, Petrels and Shearwaters of the World.Christopher Helm, London.

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Robert L. Flood, 14 Ennor Close, Old Town, St Mary’s, Isles of Scilly, TR21 0NL; [email protected] Thomas, 1 Pentland Flats, St Mary’s, Isles of Scilly, TR21 0HY; [email protected]

Appendix 1. Occurrence of Wilson’s Storm-petrel in Scillonian watersduring 2000–2006: a seven-year analysis.

Observations confirm that Wilson’s is a scarcealthough regular passage migrant off Scilly(table 4). The main period of passage peaks

from July to mid August, but numbers are vari-able between years (see also Flood & Fisher2005).

Table 4. Occurrence of Wilson’s Storm-petrel Oceanites oceanicus in Scillonian waters from short-rangepelagic trips during June to September, 2000–06 1 Total number of pelagic trips undertaken during 2000–06. 2

No. trips during which Wilson’s Storm-petrel was seen. 3 Total number of Wilson’s Storm-petrels seen duringthe week in question. 4 Percentage of trips on which Wilson’s Storm-petrel was seen.

Week commencing Cumulative weekly data

Total no. of trips1

Successful trips2

No. of birds3

% success4

25th May 4 0 0 0%

1st June 8 2 2 25%

8th June 9 3 8 33%

15th June 11 3 11 27%

22nd June 15 5 12 33%

29th June 18 8 15 44%

6th July 25 12 17 48%

13th July 29 11 18 38%

20th July 30 16 23 53%

27th July 27 13 29 48%

3rd Aug 26 13 23 50%

10th Aug 30 17 31 57%

17th Aug 29 14 26 48%

24th Aug 35 9 14 26%

31st Aug 21 3 3 14%

7th Sept 12 0 0 0%

14th Sept 2 0 0 0%

TOTAL 331 129 232

BB July 2007 5/6/07 13:31 Page 432

Three main modern-day purposes of chum-ming at sea are as follows: (a) to attracttubenoses for the thrill of seeing them close up;(b) to assist photographers; and (c) to facilitatedetailed examination and learning about identi-fication. The original purpose of chummingwas quite different, that being to aid collectionof specimens for scientific study by attractingstorm-petrels close enough to a ship to shootthem. Thus, although the purpose has changed,chumming is not a modern idea. For example,during the cruise of the whaler MV Daisy1912–13, Murphy (1915), seeking to collectLeach’s Storm-petrels, spent an hour ‘chum-ming for the birds with grease’.

The basic principle of chumming is simple.Storm-petrels can be attracted by a concoctionof smelly, fishy substances (‘chum’) that corre-sponds to a natural food source. ‘Soft’ chum, asused off Scilly, comprises ingredients likeground fresh fish, mashed rotten fish (the smellis disgusting), fish guts (the sight is disgusting),fish liver (excellent), fish oil concentrate(mainly cod liver oil, excellent), and canned sar-dines or pilchards on rare occasions when shortof the above ingredients. These ingredients areeasily mixed and pulverised. ‘Hard’ chumincludes fresh fish bones and fish heads.However, the best recipe for a chum mixremains a matter of conjecture and we do notclaim to have solved the puzzle.

Storm-petrels aresurface-feeders and it isimportant to keep chumon or near the surface.Popcorn is an effectivefloat, so we mix popcornwith soft chum to keepthe chum on the surface.Fish liver broken intotiny pieces floats natu-rally and storm-petrelsrelish it. An excellentinvestment has been thepurchase of heavy-dutychum grinders thatgrind together ingredi-ents and crush popcornto tiny pieces, infusingpopcorn pieces with ‘eaude chum’; tiny pieces aremore suitable to feeding

storm-petrels. Acquiring an effective chum-grinder is difficult; we have imported manualmachines from the USA, while motorisedgrinders are also available from the USA at apremium.

Our preferred strategy is to steam to a suit-able location and, on arrival, turn off engines,so that we drift with wind and tide. We place asoft chum mix in an onion bag tied at the top,then drop the bag over the side of the vessel justbelow the sea surface and secure it, allowing thecontents to disperse slowly. The smell attractsstorm-petrels from downwind, while the oilyslick that forms upwind is ideal for storm-petrels to pick over; it holds storm-petrels closeto the vessel, permitting thrilling views, close-up photography, and study of identificationcharacteristics.

DMS (dimethylsulphide) has been used bysome organisers of pelagic trips to attractstorm-petrels. DMS is ‘a chemical released whenphytoplankton are grazed by zooplankton …attractive to some storm-petrels’ (Brooke 2004).In special circumstances, concentrated DMScan be purchased via marine research centres ortheir suppliers. We do not use DMS since,although we have no primary source evidence,we have been warned that it is carcinogenic andin concentration harms seabirds. We are notprepared to risk poisoning seabirds or ourselves.



Appendix 2. Chum and chumming.

179. Skipper of MV Kingfisher Alec Hicks using heavy-duty manual chum-grinderimported from USA.

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BB July 2007 5/6/07 13:31 Page 433

Weather conditions can foil a chum-and-drift [Earlier the paper refers to ‘chum-and-drift’ so best to be consistent, I think.]strategy.Without a breeze, the smell of chum cannot dis-perse and the vessel will hardly drift, resultingin an oily sea surface around the vessel, but noslick. The vessel is not able to ‘advertise’ itself tostorm-petrels and very few will be present. Notsurprisingly, when steaming in calm conditionsoff Scilly we regularly encounter small flocks ofstorm-petrels sat on the sea surface, somethingrarely witnessed in breezy conditions. Whenthere is no breeze, the smell of food is not dis-tributed and temporarily the storm-petrels’extra-sensitive smelling capabilities are ren-dered redundant. Furthermore, flight withoutbreeze is relatively inefficient, since storm-petrels harness wind energy to fly (Brooke2004). Without a breeze, a storm-petrel ran-domly traversing the sea surface in labouredflight searching for food would expend muchenergy with a much reduced likelihood oflocating food. In calm conditions, it thus makessense for storm-petrels to sit tight and conserveenergy. An exception to this rule occurs whenstorm-petrels know where there is an upwellingdriven by sea currents that produces food (seebelow). Conversely, a wind of force 6 or morewill fragment the slick, resulting in pockets ofstorm-petrels all over the place, making it diffi-cult to observe and photograph them. Anotherproblem arises when, as a result of wind direc-

tion and sea currents, a slick ‘runsaway’ in the direction of the sun,which severely hampers photog-raphy. In such circumstances,steaming slowly at no more thantwo knots in the direction of the suncreates a slick in the wake of thevessel, away from the sun. Lowspeed is essential, to keep the petrelswithin close range and to preventchum washing out of the bags tooquickly. In contrast, hard chum isineffective at low speeds since thedrag is insufficient to pull morselsaway from fish bones.

When steaming out to sea, orfrom one location to another, weoften tow hard chum held in threeonion bags, one inside the other forstrength, secured to the vessel. Asmorsels slowly wash out, the vesselleaves a trail and is continually

‘advertising’ itself to tubenoses. In addition,gulls soon start to follow, acting as a visualsignal that the vessel is a food source, whichbrings in other seabirds. In the South Atlantic,we towed a large tuna (Scombridae) head,attached bones and tail, which kept (probable,see Appendix 5) White-bellied Storm-petrels inattendance for many hours. Applying the sameprinciple, sometimes we throw small amountsof soft chum over the stern on a regular basiswhen steaming.

Drifting and chumming is more successfulwhen carried out over a natural feeding loca-tion that attracts storm-petrels in its own right,such as an upwelling over a reef, a seamount, ora continental shelf where eddies might form.We visit two main reefs within easy reach ofScilly: Seven Stones reef, c. 20 km northeast ofSt Mary’s quay (where MV Torrey Canyon waswrecked) and Poll Bank c. 5 km southwest ofBishop Rock. The sea surface at these locationsis visibly more turbulent than is the case in sur-rounding waters, seemingly boiling when thereis strong tidal flow. Storm-petrels are attractedto sea currents that bring food items to thesurface and churn up nutrients, facilitatinggreater food productivity (see Haney 1985 fordiscussion of occurrence of Madeiran Storm-petrels in relation to upwelling off the coast ofsoutheastern USA).

Owing to the threats of predation, storm-petrels tend to be active around breeding



180. Seven Stones Reef, c. 20 km northeast of St Mary’s, Scilly.Thesea surface over the reef at Seven Stones is always more turbulent

than proximate waters and, when the tide runs, the sea surface overthe reef seemingly ‘boils’. Upwellings and eddies bring food items to

the surface and enhance food production. In season, European Storm-petrels Hydrobates pelagicus routinely frequent Seven Stones reef andthe location in season is good for Wilson’s Storm-petrels Oceanites

oceanicus.

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rt L

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BB July 2007 5/6/07 13:31 Page 434

colonies at dusk or after dark. During thebreeding season, many storm-petrel species dis-perse widely from colonies before dawn. Conse-quently, drifting and chumming at dusk close toan island colony will attract plenty of storm-petrels, on their way back to the colony,

although dim light means that photographicopportunities are limited. Great care should betaken after dark to avoid the possibility ofstorm-petrels and other tubenoses beingattracted to a vessel’s lights and colliding withthe ship, especially near breeding colonies.



Appendix 3. Dispelling myths.Several myths about storm-petrels seem topersist. One is that storm-petrels are afraid toapproach a vessel if there are gulls in atten-dance. However, in reality, an actively feedinggroup of gulls is a visual signal of food source toother seabirds. Shearwaters, Pterodroma petrels,skuas and even storm-petrels all use sight tosome extent to locate food and, in our experi-ence, all storm-petrel species come to chumwhether gulls are present or not.

Another apparent myth is that only certainspecies of storm-petrel come to chum. Forexample, Harrison (1983b) says that Madeiransare timid at sea, show no interest in following inthe wake of vessels, and that he has never beenable ‘to “chum” them up from a small boat’. Inour admittedly somewhat limited experiencewith Madeirans, we found that they associatewith small fishing vessels, occasionally followother ships and, off St Helena, we experienced

no difficulty in attracting Madeirans using thechumming techniques described in Appendix 2.

All storm-petrel species that we have targetedhave come to chum, although some species seemto stay longer than others. In addition to the sixspecies dealt with here, we have attracted White-vented, Swinhoe’s, Black Oceanodroma melania,Markham’s O. markhami, Hornby’s O. hornbyi,Grey-backed Garrodia nereis and White-facedStorm-petrels Pelagodroma marina using chum.Our list also includes New Zealand Storm-petrelPealeornis maoriana, until recently presumedextinct (Flood 2003; Saville et al. 2003). Webelieve that our chum and chumming tech-niques employed in the Hauraki Gulf, NewZealand, in November 2003 were prime factorsthat enticed New Zealand Storm-petrels close toour vessel, enabling us to study and photographthem and, for the first time ever, to positivelyidentify and locate a population of this species.

Appendix 4. Madeiran Storm-petrel vagrancy in Europe (excluding Portugal and the Canary Islands).

Finland• January 1993, Suonenjoki, Iisvesi. One

wrecked found in poor health on lake ice, andsubsequently died; skin preserved in KuopioMuseum (Juppinen & Collanus 1994).

France• October 1984, Chomeac, Ardeche, central

France. One wrecked found dead (Dubois etal. 2001).

• October 1987, near Hoedic Island, Mor-bihan, southern Brittany. One at sea (Duboiset al. 2001).

• August 1988, off the Sables d’Olonne,Vendee, western France. One at sea (Duboiset al. 2001).

Ireland• October 1931, Blackrock Lighthouse, Co.

Mayo. Female died after striking lighthouse

(Kennedy et al. 1954).

Spain (earliest three records precede establishment ofnational rarities committee)

• November 1951, Huelva. One storm-driven(Anon. 1951).

• February 1970, Badajoz. One wrecked(Anon. 1970).

• January 1982, Huelva. One storm-driven(Anon. 1982).

• July 1994, Pontevedra, Baiona, cabo Silleiro.One trapped for ringing on three nights(Costas et al. 1996).

• July 1994, Pontevedra, Baiona, cabo Silleiro.One, possibly female (sexed by biometrics)trapped for ringing (Costas et al. 1996).

• June 1997, Alicante, Denia. One at sea nearharbour (Koppejan 2001).

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Switzerland• December 1999, Sion Wallis. One wrecked

(Maumary & Baudraz 2000).

UK• November 1911, Milford, Hampshire. One

found dead (BOU 1971).

In addition, one is included by Brereton et al.(2003) in the list of species seen during

1995–2001 at sea in the Bay of Biscay from MVPride of Bilbao, operating between Portsmouthand Bilbao, but as far as we know this recordhas not been assessed by a national raritiescommittee. Another individual was widelyreported at sea c. 250 km west of St Mary’s,Scilly, in July 2000. We have been unable totrace the origin and check the authenticity ofthis report.



Table 5. Frequency of occurrence by month of vagrant Madeiran Storm-petrels Oceanodroma castro in Europe and Scandinavia (excluding Portugal and the Canary Islands).

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec2 1 0 0 0 1 2 1 0 3 2 1

Appendix 5. Field identification of white-bellied Fregetta storm-petrelsbreeding in the Tristan da Cunha group, South Atlantic.

Current literature suggests that both White-bellied Fregetta grallaria leucogaster and Black-bellied Storm-petrels F. tropica melanoleucabreed in the Tristan da Cunha group in theSouth Atlantic (this taxonomy is cautiously fol-lowed here). The latter taxon shows a white bellyand, not surprisingly, this has led to confusionover its taxonomic status (Marchant & Higgins1990). Some authorities consider melanoleuca asubspecies of White-bellied Storm-petrel, whileothers treat it as a subspecies of Black-bellied.Moreover, some researchers claim that onlyWhite-bellied occurs in the Tristan da Cunhagroup, others claim that both occur and breedside by side (based on measurements of size, rel-ative proportions, reticulation of tarsus, shape oftoe nails, and relative length of central toe, K.Roselaar pers. comm.).

Some specimens of Fregetta storm-petrelsfrom the Tristan da Cunha group housed in theBritish Natural History Museum are presentlyconsidered to be White-bellied Storm-petrels.However, these are currently undergoing molec-ular analysis to resolve debate over the relation-ship between these and melanoleuca andleucogaster (B. Stephenson pers. comm.). Untilresolved, field identification of any white-bellied Fregetta storm-petrel in the NorthAtlantic remains problematic (and molecularresolution may well not solve the problem offield identification). Thus, some authorities,including BWPi, consider the White-belliedStorm-petrel claim north of Cape Verde Islands

on 17th August 1986 to be unsafe. Conversely,the black belly-stripe of Black-bellied Storm-petrel is diagnostic, so the two records offNorth Carolina, both photographed and clearlyshowing this plumage feature, are irrefutable.

At present, if a white-bellied Fregetta storm-petrel were to be encountered in the NorthAtlantic, the best course of action would be todocument the event thoroughly then sit backand watch the taxonomic developments. Ideally,documentation should include detailed notesand a portfolio of illustrations. On the basis ofextant literature concerning the separation ofthe two species, it is especially important todocument the following:

• Back and upperwing colour and colourtones: these are darker and warmer brown inBlack-bellied, paler and greyer in White-bellied (Shirihai 2002).

• Toe projection: the two species are appar-ently separable by the position of the feet inrelation to the tail (Marchant & Higgins1990), the toes projecting noticeably beyondthe end of the tail in Black-bellied, but atmost only marginally in White-bellied.

• White fringes of back and scapulars: White-bellied shows fringes c. 2.0 mm wide in freshplumage, and the covert bars are more con-spicuous than those of Black-bellied, whichshows narrower fringes c. 0.5 mm wide infresh plumage (K. Roselaar pers. comm.).Caution is required here since white fringesabrade over time.

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Identification pitfalls arise when a storm-petrel’s remiges are heavily worn and/or inmoult. Timing of moult depends on age and isspecies-dependent. The flight action and jizz ofa storm-petrel with heavily worn and moultingflight feathers is different from that of the samespecies with fresh flight feathers. For example,during a southwest gale in September 1978, atMorecambe Bay, Lancashire, Marsh (1980)observed the flight action and jizz of a Leach’sStorm-petrel sufficiently altered by moult that itcould easily have been misidentified:

The odd bird appeared noticeably round-winged and consequently straighter-forewinged than a typical Leach’s; its tailappeared to be shorter and more square-endedthan Leach’s; and it possessed the faintestgreater-covert bar of all the petrels seen thatday; rather like a typical [European] Storm-petrel and thus invisible at a range of over 100m. Any excitement was dampened by the fact itwas obviously the same size as theaccompanying Leach’s Petrel and their whiterumps appeared identical … I was able toobserve it flying some 5 m below me… I wasable to see a gap in the wing about halfwayalong the secondaries and note the tail asscruffy and irregular: characteristic of activemoult. … The round wings were still obvious,but could surely be explained by a bird still re-growing its outer primaries.

It is conceivable that this storm-petrel couldhave been mistaken for a Madeiran at distance.It looked strange among Leach’s, butwas also rounder-winged withstraighter forewings, had a shorter,more square-ended tail, and showedonly a faint greater-covert bar on theupperwing. Such characteristics onpaper better portray Madeiran thanLeach’s.

This incident parallels our expe-riences off Scilly with Wilson’sStorm-petrels. Adult Wilson’s moulttheir flight and body feathers duringMay–September, when present inScillonian waters (moult timing andstrategy of immatures between theirsecond calendar-year and adulthoodhas not been published). Conse-quently, especially early in the‘Wilson’s season’, we see adult andpresumably immature (not juvenile)



Appendix 6.Wear, moult and bleaching.

181. European Storm-petrel Hydrobates pelagicus, off Scilly,August2003. It is incredible just how worn a storm-petrel can become

during the breeding season and still be able to fly.This European wasvery heavily worn, which strongly affected its flight behaviour.

Brya

n Th

omas

Wilson’s that are heavily worn and others thatare in moult, with a mixture of worn and freshfeathers (e.g. plate 177 in Boswall 1979; Sibley2000), as well as presumed juveniles that havefresh flight and body feathers (H. Shirihai pers.comm.). The flight action and jizz of Wilson’swhen heavily worn or in moult looks decidedlyunlike that of birds with a full set of fresh flightfeathers. Heavily worn and moulting Wilson’stend to be less stylish, less accomplished; theirflight becomes more fluttering and can evenconvey the feel of European Storm-petrel.

Plumage is also affected by wear andbleaching, so that black-brown becomes virtu-ally brown. Wear has a strong influence on thevisibility of certain plumage characteristics,especially the greater-covert bars of Wilson’s,which become paler through bleaching but lessextensive through feather wear. A Wilson’s withreduced greater-covert bar and heavily wornflight feathers may convey the jizz and feel of aEuropean Storm-petrel and can be misidenti-fied, especially if the legs are retracted! Con-versely, bleached brown greater coverts on anadult European Storm-petrel may suggest dullwing-covert bars, while at the same time under-wing-covert panels are worn and hard toobserve. Occasionally, a European will glidemore than usual and, if showing a dull upper-wing-covert bar and apparent lack of whiteunderwing panels, it could be misidentified as aWilson’s!

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Other examples of the effects of bleachingand wear include the increasingly pale greater-covert bars of Leach’s that eventually start todisappear with wear, and the similar effects onthe white greater-covert pencil lines of

Madeiran and pale mantle and scapular featherfringes of White-bellied and Black-belliedStorm-petrels.

Awareness of the timing of moult is impor-tant. It highlights potential identification errors



019. Wilson’s Storm-petrel Oceanites oceanicus, off Scilly, July 2005.This Wilson’s is in moult and has dropped allits old primaries bar P8–10 on the left wing and P7–10 on the right wing. Note the moult contrast between old,bleached brownish outer primaries and fresh dark-looking black-brown inner primaries.The flight of a Wilson’s inextensive primary moult, and/or with heavily worn primaries, is less accomplished and more fluttering, to someextent conveying the jizz of a European Storm-petrel Hydrobates pelagicus.A fluttering Wilson’s that also shows

significantly reduced greater-covert bars and has its legs retracted or minimal toe projection, like this one, can bemisidentified as a European Storm-petrel!

Brya

n Th

omas

Table 6. Timing of moult of flight feathers for adult (Ad) and second-calendar-year (2CY) European Hydrobates pelagicus, Leach’s Oceanodroma leucorhoa, and Wilson’s Storm-petrels Oceanites oceanicus:

dark grey = main period of moult, light grey = marginal period of moult, white = normally not moulting.Sources: BWPi 2006 and our own observations of European and Wilson’s off Scilly. Note that adult and

second-calendar-year moult cycles are not synchronised. Moult begins progressively later in years following the second calendar-year. Storm-petrels start to breed at four or five years old, by which

time moult is synchronised with that of adults.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

European Ad

2CY

Leach’s Ad

2CY

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Wilson’s Ad

2CY

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caused by moult and wear and suggests likelyspecies for the time of year. Table 6 summarisestiming of flight-feather moult of European,Leach’s and Wilson’s Storm-petrels. Madeiran isexcluded because of complications of the ‘time-

share’ breeders on the Azores, while Black-bellied and White-bellied Storm-petrels areobviously different from the other four speciesdiscussed here.



Appendix 7. Size illusion and exaggeration.On short-range pelagic trips from Scilly wehave watched many Wilson’s Storm-petrels, atall visible ranges and often for hours alongsideEuropean Storm-petrels, feeding over oily slicksand around the vessel. Given suitable condi-tions, we can pick out Wilson’s from Europeanat 400 m on size (Wilson’s looks noticeablylarger than European), as well as on flightaction and various flight profiles. Wilson’sappear larger than Europeans than ratio com-parisons of body length and wingspan suggest isactually the case. Participants on our pelagictrips typically estimate Wilson’s as up to half aslarge again as European (i.e. perceivedwingspan ratio up to 1.5), whereas the actualwingspan ratio is around 1.05 (table 2).

Moreover, we have observed several Leach’s

alongside European Storm-petrels. An overallimpression is that Leach’s approach twice thesize of European (i.e. perceived wingspan ratioup to 2.0) but, as with Wilson’s, the actualwingspan ratio is significantly less, around 1.21.In our experience, there seems to be a relativesize illusion between storm-petrel species whenobserved together at sea and so consciousawareness of this phenomenon when faced with‘something different’ is important in preventingsize exaggeration. Size illusion may have playeda part in the perceived size of the ‘Chalice petrel’and is relevant to the debate on the identifica-tion of that bird (e.g. British Birds RaritiesCommittee’s files 1997; Force 1997; Young &King 1997; Garner & Mullarney 2004).

Appendix 8. Factors of scale.Something to be considered when judging thesize of storm-petrels at sea is apparent size vari-ation resulting from scale. Scale is determinedby two factors: (a) the size of vessel from whichobservations are made, and (b) the size of prox-imate seabirds. To us, Wilson’s Storm-petrel offScilly appears as an intermediate-sized storm-petrel and never small. Our vessels MV King-fisher and MV Sapphire are about 16 m inlength and 6 m across the beam, eye-level isabout 4 m above the sea surface and distance ofWilson’s from the vessel often about 10–20 m.Nearby seabirds range in size from EuropeanStorm-petrel to Northern Gannet Morus bas-sanus (e.g. wingspan range from c. 380 mm to1,720 mm), and Wilson’s is therefore not thesmallest species present.

However, Wilson’s appears small, evenminiature when the vessel and proximateseabirds are on a grander scale. ObservingWilson’s from the bridge and upper decks ofMV Professor Molchanov in the South Atlanticin 2006 was a reminder of this phenomenon.

This boat is 71.6 m in length and 12.8 m acrossthe beam, eye-level is about 20 m above sealevel, and distance of Wilson’s from the vesseloften 60 m or more. Nearby seabirds range insize from Black-bellied Storm-petrel to Wan-dering Albatross Diomedea exulans (e.g.wingspan range from c. 400 mm to 3,500 mm),where Wilson’s was indeed the smallest speciespresent). Wilson’s seemed to be much smaller inthe southern oceans than off Scilly in thecontext of this grander scale.

The point that we wish to emphasise is thatWilson’s Storm-petrel can appear as an interme-diate-sized storm-petrel and as a small storm-petrel, depending on prevailing factors of scale.Such a phenomenon of course applies to allstorm-petrels under consideration in thisarticle. For example, we venture to suggest thatShirihai’s (2002) observation that Black-belliedStorm-petrel’s ‘size at sea never appears as largeas measurements suggest’ is, in part at least, aresult of factors of scale.

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Arcing back Typical feeding behaviour ofWilson’s, after slowly working and feeding itsway forward into the wind over a foodsource; it doubles-back on itself to the originof the food source by flying a wide arc closeto the sea surface, then starts feeding again.

Bouncing Typical feeding behaviour ofWilson’s, comical bouncing up and down onspringy legs as if on a pogo stick, whilstmanoeuvring over food source.

Bounding Typical flight behaviour of Leach’s, aspringy wing-and-body movement upwardsand/or forwards.

Bowed wings Structural characteristic of Euro-pean, Leach’s and Madeiran, holding eachwing in a shallow bow-like concave curve, sothat the two wings form a shallow-M profilewhen seen head-on or tail-on; the depth ofthe ‘M’ is always shallow, but varies to someextent among species.

Buoyant Typical flight behaviour of Leach’s thatmakes it seemingly float in the air.

Dancing Typical feeding behaviour of Wilson’s,in what seems to be choreographed stepsand body movements whilst manoeuvringover food source and taking food items.

Darting Typical flight behaviour of Leach’s,much less so Madeiran and Wilson’s, sud-denly dashing off in an apparently randomdirection.

Dead halt Ability of storm-petrels to stopalmost instantly when locating a food item.The energy of forward motion is dissipated,forcing the storm-petrel upwards beforedropping down directly over food item.

Deep wingbeats Most typical of Leach’s, wherewings are raised high on the upbeat anddepressed low on the downbeat.

Dipping head Characteristic food-gatheringaction of all storm-petrels, where the head isquickly moved down to the sea surface toseize or snatch a food item, then lifted backup again.

Direct Most typical of travelling Wilson’s, flyingpurposefully forwards for some time as ifflying along an imaginary straight line.

Diving Behaviour of European, Wilson’s, andMadeiran (and possibly the three otherspecies), diving below sea surface to collectfood item, probably no deeper than 1 m, forjust a short period of time, using wings to

swim underwater.Elastic wings Typical of Leach’s, where flexible

use of springy wings makes the wings appearas if made of elastic.

Erratic Typical flight behaviour of Leach’s,where progress forwards appears disorderlywith unpredictable changes of speed and/ordirection.

Fluttering Typical flight behaviour of European,far less so of Wilson’s, in utilising rapid,shallow, flickering wingbeats.

Following Typical of European, Wilson’s, andthe two Fregetta species, less typical ofLeach’s and Madeiran, following vessels andassociating with feeding cetaceans, bene-fiting from food scraps (a) brought tosurface by a vessel’s propellers and bowwave, (b) fish waste from trawlers, and (c)fish debris and leftover minutiae fromfeeding cetaceans.

Foot-pattering Typical feeding behaviour ofstorm-petrels (although much less so in thecase of Madeiran and the two Fregettaspecies), where legs and feet work rapidly‘running-on-the-spot’ over a food item,accompanied by wing actions helping astorm-petrel to remain level and stable, andto hover or hang over food items in order toseize or snatch them.

Gliding Typical flight behaviour of storm-petrelspecies (but less so for European), where thewings are held outstretched and roughlyhorizontal and the aerodynamics of thewings and wind over the water are used toallow a bird to glide over the sea surface.

Hanging Typical flight behaviour of feedingWilson’s and Leach’s, possibly others,whereby the wings are held outstretched butstill and the wind is utilised to maintain asteady position over a food source(employing the same principle as hang-gliders).

Hopping Typical flight behaviour of Wilson’sand the two Fregetta species; whilst glidingand skimming, using one foot on an out-stretched leg to hop over the sea surface tomaintain height and momentum and assistwith direction changes.

Hovering Typical flight behaviour of feedingEuropean, Leach’s and, to some extent,Madeiran, less so for other species, flapping



Appendix 9.Terminology used to describe flight behaviour of storm-petrels.

BB July 2007 5/6/07 13:31 Page 440

wings to maintain a steady position over afood source.

Hugging Typical flight behaviour of Fregettaspecies, which consistently hug the seasurface, skilfully traversing wave contours.

Leaping Typical flight behaviour of Leach’s andto a much lesser extent Madeiran; likebounding, with a springy wing-and-bodymovement upwards and/or forwards, butsudden and startling as if jumping an imagi-nary hurdle unexpectedly encountered.

Purposeful Flying in a determined fashion as ifheading to a predetermined destination.

Running Typical feeding behaviour of Wilson’s,possibly others; while gliding, the bird runsalong the sea surface with wings out-stretched dipping head to seize food items.

Seizing food items Essential feeding behaviourof all storm-petrels whereby the head isdipped and the bill used to seize, snatch, oreven to pull at food items on the sea surface.

Series of wingbeats A definite number of wing-beats.

Shallow wingbeats Typical of European,Wilson’s, and Madeiran at least, where thewings are raised only slightly above the hori-zontal on the upbeat and depressed only alittle below the horizontal on the downbeat.

Shearing Typical travelling flight of storm-petrels in strong winds, although less so inEuropean, tilting one way and then another,whilst gliding on stiff-looking wings, ratherlike a small Puffinus shearwater.

Skimming Typical flight behaviour of Wilson’sand the two Fregetta species, gliding low overand indeed nearly touching sea surface, facil-itating hopping, running and skipping.

Skipping Typical flight behaviour of Wilson’sand the two Fregetta species; as hopping, butusing left and right legs and feet to skip overthe sea surface to maintain height andmomentum.

Snatching Typical feeding behaviour of storm-petrels, although less so for European; whilstskimming, the bird dips its head andsnatches a food item from the sea surface inits bill.

Splashing Typical feeding behaviour of the twoFregetta species and sometimes Wilson’s,whereby the breast is used rather than thelegs and feet in skimming flight to splash(bounce) the bird off the sea surface.

Steady wingbeats Regular unchanging wing-beats.

Stiff wings Typical of Wilson’s, where apparentinflexibility of wings makes them appear asif without working joints.

Strong flight Typical flight impression given bylarger storm-petrels, when they look vig-orous, energetic, and powerful for their size;often observed in strong winds.

Swooping Typical feeding behaviour of Leach’s,involving swoops back and forth over fooditem whilst lunging at it.

Weak flight Typical flight impression given byEuropean, appearing feeble, but actually sur-prisingly robust in strong winds.

Zigzagging Typical flight behaviour of Euro-pean, Madeiran, and two Fregetta species;forward progression is accomplished by firstbanking to the left, then to the right, and soon, as if following an imaginary criss-crosspath.



Appendix 10.Angle of view.The angle of view is particularly relevant tostorm-petrel identification, since the birdsoccupy the lowest 10-m band of airspace abovethe sea surface, with most rarely rising above 5 m (and often remaining below 2 m). The totalexperience of a storm-petrel from larger vesselslike RMS Scillonian III is different from thatfrom smaller vessels like MV Sapphire, used forpelagic trips off Scilly.

Estimating the angle of view is helpful instorm-petrel identification since it determineswhat an observer might be expected to see onthe bird (also determined by range, duration ofobservation, and flight behaviour, of course).

Imagine you are observer (a) in fig. 1, where theangle of view is shallow, watching a NorthAtlantic Oceanodroma and you observe thatwhite in the region of the tail is seeminglyalways in view. Such an observation stronglysuggests you are watching a Madeiran Storm-petrel. Leach’s has minimal white extensionsfrom the rump to undertail-coverts and rearflanks, and the white rump-patch is often diffi-cult to see, even at close range. However, withMadeiran, white wraps around the rump to theundertail-coverts and rear flanks, which is rela-tively easy to see even over a considerable range(pers. obs.).

BB July 2007 5/6/07 13:31 Page 441

Angle of view will affect the relative ease withwhich certain important features can be seenand documented. A shallow angle of viewmakes the following relatively difficult to see:

• structure: travelling wing shape, tail shapeand toe projection;

• plumage: wing-covert bars and white onrump and uppertail-coverts; and

• moult and wear of remiges and rectrices.A deeper angle of view makes the following

relatively difficult to see:

• structure: bill shape and proportions;

• plumage: underwing-covert and axillarypanels and extent of white on undertail-coverts and rear flanks, and white on belly.



Fig. 1. An observer aboard MV Sapphire (left) has a shallow angle of view (‘x’) to the storm-petrel,while an observer aboard RMVScillonian III (right vessel) is higher above the sea surface and closer

to the storm-petrel resulting in a deeper viewing angle (‘y’).

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identification of ‘black-and-white’ storm-petrels of the...

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