the strange world of gull identification nick rossiter october 2001

The Strange World of Gull Identification

Nick Rossiter

October 2001

Great Advances

• Moult much better understood

• All ages considered

• Seasonal changes dealt with

• Much more information on Herring Gull/LBB complex world-wide:– accounts of Mediterranean YLG, Caspian Gull,

Baraba Gull, Mongolian Gull, American Herring Gull

Problems

• Later!!

http://www.zestforbirds.co.za/Zest for Birds

Mystery gull no. 5

Can you tell us what this gull is? It wasphotographed in Walvis Bay in Namibia in April2000. We would like to hear your comments onwhat it is and why you say so as well, so pleaseemail us your answer with reasons and we willput them all together and post them to thispage.

For Black-headed Gull:

From Kevin Caley of the U.K.:

This is a black-headed gull, a very common specieshere in Britain.

Note the slender bill, with its dark tip (only found inimm and winter birds) and the two dark patchesabout the eye and at the back of the ear coverts,characteristic for this species in winter plumage.The most telling feature, however, is seen on theopen wing - the triangle of white on the leadingedge, combines with the black tips to the first fourprimaries (counting inwards from the leading ege)are diagnostic for this species, ad cannot beconfused iwth any other species, European orAmerican.

From Verbanck Koen of Belgium:

This is an adult Black-headed Gull (Larusridibundus) in winter plumage. Identification israther straightforward:-typical silhouette-wing-pattern: black on outer web of the first primaryand primary tips inwards as far as 6th-(to 8th).Remainder of the wing pale grey with thin whiteleading and trailing edges.-tail: all white-bare parts: bill red with dark tip; and legs darkreddish coloration-typical (winter plumage) head-pattern: white head,with dusky eye-crescent, prominent blackish ear-spot (often with faint grey extension over rearcrown)

For Grey-headed Gull:

From Nick Rossiter of the U.K.:

Grey-headed Gull -- adult in post-breeding moult.

White is on P5-P7 which is right for Grey-headed Gulland wrong for Black-headed Gull where the white ison P7-P10. Black bar on P4 is also OK for Grey-headed. The extensive black near the tip on the whitefeathers is also right for Grey-headed.

The state of moult in April is right for a southernhemisphere breeder. The characteristic mirrors on P9and P10 of Grey-headed are missing because thesefeathers have been shed and not yet re-grown.

For hybrid Grey-headed x Black-headed Gull:

From Igor Festari of Italy:

Even at first sight, become obvious that's not atypical winter-plumaged Black-headed or Grey-headed Gull; it shows absolutely atypicalcolouration, with some important feature almostintermediate between the two:

- Structure: structure is typical for Grey-headed,with long neck and tail, small headed appearanceand very long legs (especially the tibias); also thebill is too long and has sligthly too broad base anddecurve tip for a Black-headed (more Grey-headed-type). Wings, at the contrary, are moulting primariesbut they still appear too short-handed, broad-armedand pointed for a classic Grey-headed (andtherefore more similar to Black-headed's).

Received more recently from David Allen ofSouth Africa:

This is a Grey-headed Gull. The photo does notreally show the leading edge of the wing well at all.It is probably about one year old. They are winterbreeders so an April date would fit this. Thereforeit's in transition between adult and juv. features, i.e.has dark eye and two-tone bill of juv. but bodyplumage and tail of adult. Hard to tell about theleading edge of the primaries and juv. Grey-headedGulls lack have the mirrors in the primaries ofadults. Essentially there are hundreds of birdslooking just like this in Durban Bay every summer.Head pattern fits a non-breeding Grey-headedperfectly. The hybrid theory is certainly novel butthe breeding grounds of the two species areseparated by the Sahara!

Grey-headed Gull Adults, Gambia, August 1999

Moult in Large Gulls

• Juveniles: (first-generation)– scapulars, back, coverts (post-fledging)

• First-winter: (second-generation)– scapulars, back, coverts (continuous)– primaries (spring, summer)

• (First-summer -- fading, bleaching)

• Second-winter (third-generation)

Timing is Very Variable

• Northern forms (e.g. Scandinavian argentatus, Glaucous Gull) may retain juvenile feathers to late winter or spring

• Southern forms (e.g. Mediterranean Yellow-legged Gull) moult many juvenile feathers in late summer/ early autumn

• Primary moult seems more independent of latitude

Juvenile ‘Yellow-legged Gull’ La Linea August 2001

Juvenile ‘Yellow-legged Gull’ Estepona August 2001

‘Caspian Gull’ Norway, First-winter, February 2001 (Frode

Falkenberg)

First-winter ‘Yellow-legged Gull’ San Sebastian, February 2000 (Dick Newell)

Matosinhos, First-winter/1s ‘Yellow-legged Gull’, April 2001

First-winter/1s ‘Yellow-legged Gulls’ (with 2s LBBG), Porto, April 2001

First-winter/1s ‘Yellow-legged Gull’ Fuerteventura, April 1999

Four First-summer ‘Yellow-legged Gulls’ Fuerteventura, April 1999

Two first-summer/2w Yellow-legged Gulls michahellis Royan, August 1991

First-summer ‘Yellow-legged Gull’ Lanzarote, August 1992

First-summer/2w ‘Yellow-legged Gull’ Lanzarote, August 1992

First-summer ‘Yellow-legged Gull’, Tenerife, July 2000

First-summer/second-winter ‘Yellow-legged Gull’ Estepona August 2001

Second-winter ‘Yellow-legged Gull’ Fuerteventura, September 2000

Second-summer ‘Yellow-legged Gull’ Porto, April 2001

Second-summer ‘Yellow-legged Gull’, Essaouira, April 2000

Third-winter ‘Yellow-legged Gull’, Gran Canaria, September 2000

Fourth-summer ‘Yellow-legged Gull’, Matosinhos, April 2001

Adult summer ‘Yellow-legged Gull’, Agadir, April 2000

Part 2

Forms of Yellow-legged Gulls

Adult Mediterranean michahellis, Royan, August 1991

Adult/3s-4w Mediterranean michahellis, Royan, August 1991

Two first-summer/2w Mediterranean michahellis Royan, August 1991

Map for Atlantic Forms

Adult ‘Yellow-legged Gull’ atlantis, Tenerife, August 1998

Adult ‘Yellow-legged Gull’ atlantis, Tenerife, December 1996

Adult ‘Yellow-legged Gull’ atlantis, Lanzarote, August 1992

Table 1: Biometrics (in mm) of Herring L .a. argenteus, Yellow-leggedand Lesser-black Backed Gulls L. f. graellsii.

Feature argen-teus

Medi-terraneanYellow-leggedGull

micha-hellis

Atlantic Yellow-legged Gull graell-sii

NWIberia

W Iberia NWAfrica

Macro-nesia

Source Cramp(1983)

Cramp(1983)

Carreraet al(1987)

Cramp(1983)

Urban etal (1986)

Cramp(1983)

Cramp(1983)

wing 404-425

438-460 419 401-431 420-439 423-437 406-427

tail 160-170

169-179 - 158-169 162-170 165-173 152-164

bill 48.9-53.2

51.5-56.6

54.8 49.5-53.6

49.4-55.7

49.1-51.5

47.7-52.1

tarsus 60.5-65.2

64.5-70.6

65.6 60.3-64.4

61.6-65.0

62.7-64.7

60.3-65.2

toe 56.7-61.6

59.2-65.4

- 55.2-59.3

- 58.7-60.3

52.5-56.3

Table 2a: Further Biometrics (in mm) of Atlantic Islands Yellow-leggedGulls.

Feature Atlantic Islands Yellow-legged Gull

Macro-nesia

Azores Azores Canaries(East?)

Canaries-Tenerife

Azores

Source Cramp(1983)

Dwight(1922)

Dwight(1925)

Banner-man(1963)

Volsøe(1951)

Vaurie(1965)

wing 423-437 401-423 402-421

401-418 417-440 418-438

tail 165-173 162-170 162-171

162-170 - -

bill 49.1-51.5 50.3-55.1 50.2-54.3

46.5-54 - -

tarsus 62.7-64.7 61.7-66.6 61.6-66.3

62.5-65.5 - -

toe 58.7-60.3 52.3-56.0 52.2-55.2

- - -

Table 2b: Further Biometrics (in mm) of Mediterranean Yellow-leggedGulls.

Feature Mediterranean Yellow-legged Gull

Medi-terranean

Camargue BalearicIslands

IslasCharafinas

Source Cramp(1983)

Isenmann(1973)

Carrera(1987)

Carrera(1987)

wing 438-460 440-465 447 457

tail 169-179 - - 178

bill 51.5-56.6

56-61 57.4 56.6

tarsus 64.5-70.6

67-72 70.3 68.5

toe 59.2-65.4

- - -

Juvenile ‘Yellow-legged Gull’ atlantis, Tenerife, August 1998

Three Adult Atlantic Yellow-legged Gulls, Agadir, April 2000

Typical Adult Wingtip ‘Yellow-legged Gull’, Agadir, April 2000

Typical Adult Wingtip ‘Yellow-legged Gull’, Fuerteventura, April 2000

Table 4: Percentage of Wingtip Patterns by Location for Adult Atlantic Yellow-legged Gulls.

Area P10 P9 P6-P10 P5 P4 S Tip

(%)LM(%)

SM(%)

M(%)

S Sol-id(%)

SI(%)

LI(%)

S BB(%)

TB(%)

IM(%)

PN(%)

SanSebastian

6 85 15 0 85 7 0 30 70 6 15 35 50 15

Santander 21 70 30 0 85 21 0 30 70 10 0 80 20 0Porto/Minho

52 15 85 + 35 32 55 40 5 28 50 30 20 15

Setúbal /Lisbon

18 35 65 0 50 18 50 35 15 20 60 10 30 0

Faro 11 20 60 20 10 12 100 0 0 14 85 15 0 15Andalucia 6 50 50 0 15 6 100 0 0 6 100 0 0 100Tanger 19 50 45 5 35 10 60 30 10 17 50 40 10 40Asilah 4 25 75 0 0 4 100 0 0 2 50 50 0 -Agadir/Essaouira

76 55 40 5 25 71 90 10 0 69 35 30 35 10

Fuerte-ventura/Lanzarote

31 30 60 10 30 39 80 15 5 38 55 30 15 15

GranCanaria

56 45 50 5 25 71 80 20 + 63 40 35 25 15

Tenerife/Gomera

84 40 50 10 20 31 95 5 0 49 45 30 25 5

La Palma/El Hierro

17 60 20 20 10 4 100 0 0 14 65 35 0 5

Cantabrican 27 73 27 0 85 28 0 30 70 16 6 63 31 10W Portugal/NW Spaincline

70 19 80 1 39 50 54 37 9 48 54 21 25 10

Dark 279 45 47 8 23 232 87 12 1 249 46 30 24 11Med.intersection

25 51 45 4 31 16 76 18 6 23 61 31 8 57

All forms 401 43 51 6 30 326 74 18 8 336 46 31 23 13

Comparative Wingtip Data

• None available from core area of Mediterranean Yellow-legged Gull in western Mediterranean

• Some data from putative michahellis in northern Europe.

• Are northern European birds typical?

• Birds of known origin are emphasis of current work (e.g. IGM V)

Adult ‘Yellow-legged Gull’, Faro, March 1999

Two Adult ‘Yellow-legged Gull’, Setubal, March 1999

First-winter/1s ‘Yellow-legged Gulls’ (with 2s LBBG), Porto, April 2001

Matosinhos, March 2001, smithsonianus, intermedius, graellsii, ‘YLG’

Matosinhos, March 2001, ‘YLG’ adult, ‘Big Waters Gull’.

Part 3

Northern Forms, Med/Atlantic Intersection and Summary

Porto, March 2001, Pair ‘YLG’ adults

Minho, April 2001, ‘YLG’ adult

Noja (Santander), August 1990, 3s ‘YLG’

San Sebastian, February 2000, ‘YLG’ adult (Dick Newell)

Table 3: Comparability of Long and Mew Calls of Adult Atlantic Yellow-legged Gulls to LesserBlack-backed Gull L. f. graellsii, Herring Gull L. a. argenteus and Mediterranean Yellow-legged

Gull L. michahellis

Area Long calls % like Mew calls % likegraellsii Shrill

graellsiiDeepargenteus

Mediterraneanmichahellis

graellsii argenteus Mediterraneanmichahellis

Santander 0 0 100 0 0 100 0Porto/Minho + 45 55 0 75 25 0Setúbal /Lisbon 0 90 10 0 95 5 0Faro 20 70 10 0 100 0 0Tanger 0 92 8 0 100 0 0Agadir/Essaouira

0 90 10 0 100 0 0

Fuerteventura/Lanzarote

0 20 80 0 35 65 0

Gran Canaria 0 20 80 0 45 55 0Tenerife/Gomera

0 80 20 0 100 0 0

La Palma/ ElHierro

40 60 0 0 100 0 0

Cantabrican 0 0 100 0 0 100 0W Portugal cline + 68 32 0 85 15 0Dark 10 57 33 0 80 20 0Med. intersection 0 92 8 0 100 0 0All forms 6 57 37 0 75 25 0

Map showing Areas for Forms

‘YLG’: Mauritania, Azores; Kelp Gull (Birding World)

Separating dark form from michahellis

C. michahellis by their:

1. smaller size by 5-10%;2. less attenuated appearance at rest;3. shorter legs, typically 70% of height of body above legs compared to about 100%;4. rounded heads, lacking angular appearance;5. blunt wingtip giving bunched primary tips on the folded wing;6. smaller white primary tips on the folded wing;7. slightly darker mantle shade with a marked blue-grey sheen;8. shriller long calls lacking a guttural component, less deep mew calls,9. long calls given at 60 rather than 90 ;10. ochre tint to the yellow legs;11. less white in wingtip with only 25% carrying a mirror on P9.

Intersection Area -- Atlantic / Mediterranean

• Do they mix?

• Do the breeding areas overlap?

• Are there intermediate forms?

Tanger, August 2001, Adult ‘YLG’

Tarifa, August 2001, Adult ‘YLG’

Tarifa, August 2001, Two Adult Mediterranean YLG

Comparison Med/Atlantic YLG adults, Conil, August 2001

Conil, west Andalucia

Gibraltar from La Linea

Gibraltar, June 1994, Adult + chick ‘YLG’ (Tom Cadwallender)

Estepona, east Andalucia

Estepona, August 2001, Adult ‘YLG’

Estepona, August 2001, 2s/3w ‘YLG’

Estepona, August 2001, ad + imm ‘YLG’

Strange World?

• Because too many id criteria rely on studies of migrants to northern Europe, rather than of populations in their native areas.– Such migrants are putative– Main forms described but variation cannot be

determined reliably– Even marked/ringed individuals may not be

typical of the ones that stay at home

Current situation

• Difficult

• Forthcoming BB paper based on studies of populations to the east rumoured to question id of Caspian Gull

• Work to the west (as here) shows definition and id of Western Yellow-legged Gull to be far from settled

The End

of the Seagull Story

the strange world of gull identification nick rossiter october 2001

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