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Relative Distribution and Abundance of Wintering Raptors inAgricultural and Wetland Landscapes of South FloridaAuthor(s) Elise V Pearlstine Frank J Mazzotti Mary Hudson KellySource Journal of Raptor Research 40(1)81-85 2006Published By The Raptor Research FoundationDOI httpdxdoiorg1033560892-1016(2006)40[81RDAAOW]20CO2URL httpwwwbiooneorgdoifull1033560892-101628200629405B813ARDAAOW5D20CO3B2

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J Raptor Res 40(1)81ndash85

E 2006 The Raptor Research Foundation Inc

RELATIVE DISTRIBUTION AND ABUNDANCE OF WINTERING RAPTORS IN AGRICULTURAL AND WETLAND LANDSCAPES

OF SOUTH FLORIDA

ELISE V PEARLSTINE1 FRANK J MAZZOTTI2 AND MARY HUDSON KELLY

University of Florida IFAS Ft Lauderdale Research and Education Center 3205 College AvenueDavie FL 33314 USA

KEY WORDS American Kestrel Falco sparverius TurkeyVulture Cathartes aura Red-tailed Hawk Buteo jamaicensishabitat use agriculture perch choice south Florida Everglades

South Florida provides important winter habitat fora variety of migratory and resident raptor species (Bohalland Collopy 1984) In this area habitat loss has occurredas natural habitat has been modified for either agricultureor urban use Two predominant features of the currentvegetated landscape are Everglades wetland communitiesand agricultural areas (Pearlstine et al 2001) includingsugarcane-dominated (Saccharum sp) fields south and eastof Lake Okeechobee in the Everglades Agricultural Area(EAA) Although the two habitats are open and containsuperficially similar components such as upland wetlandtemporary and permanent water and sparsely-distributedtrees structure and composition varies greatly betweennatural and agricultural habitat

Roadside surveys are convenient for obtaining informa-tion on distribution population trends and abundance ofraptors (Fuller and Mosher 1981) Such surveys have beenused extensively to determine relative abundance (egWoffinden and Murphy 1977 Leptich 1994 Eakle et al1996 Meunier et al 2000) population trends (eg Layne1980) habitat associations (eg Preston 1990 Sorley andAnderson 1994 Garner and Bednarz 2000 Thiollay andRahman 2002) perch use (eg Bohall and Collopy 1984Smallwood et al 1996 Meunier et al 2000 Leyhe andRitchison 2004) activity patterns (eg Meunier et al2000) and species richness and diversity (eg Leptich1994 Sorley and Anderson 1994) However a number offactors may cause variation in raptor counts includingdifferences in detectability across cover types distance ofobservation (Millsap and LeFranc 1988) and time of day(Bunn et al 1995)

Migratory and wintering hawks begin arriving in southFlorida in October and are present throughout the winterThey can be easily observed along roadsides and flyingover the landscape The purpose of our study was to

compare relative distribution and abundance of commonwintering raptors in agricultural and wetland landscapesOur null hypotheses were that there was no difference inraptor abundance and diversity between the two habitatsand that perch types were chosen randomly

METHODS

Study Area Historically south Florida was dominatedby the greater Everglades ecosystem From Lake Okeecho-bee southward water flowed across a wide landscape ofmarshes sloughs tree islands and mangrove swamps intoFlorida Bay (Porter and Porter 2002) Before the turn ofthe century drainage of the northern part of theEverglades commenced with production of a system ofcanals and dikes in the vicinity of and around LakeOkeechobee The EAA came into being in the early 1950s(Light and Dineen 1994) The major road through thesetwo habitat types is US Route 27 a four-lane dividedhighway passing through two counties Palm Beach Countyto the north and Broward County to the south The countyline follows a demarcation between agriculture and Ever-glades vegetation Vegetation along the roadside consistsof mowed strips powerlines trees and shrubs of mostlyexotic species and canals Beyond the canals thelandscape is dominated either by huge expanses ofagricultural fields or of natural marsh and tree islandsboth habitats are open with few scattered trees

The EAA dominates western Palm Beach County and iscomprised mostly of sugarcane fields with a small percent-age of other crops including rice sod and variousvegetables (Izuno et al 1991) The agricultural fields areintermixed with a grid system of unpaved roads perma-nent canals and shallow ditches that provide varyingdegrees of irrigation and drainage for the fields Thissystem of fields and canals produces a patchwork ofagricultural crops with field and canal-edge cover consist-ing of herbaceous and shrubby vegetation usually exoticspecies and sparse trees

A single large canal on the east side of the road in PalmBeach County was fringed by tall brush and short treessome of which were dead and used as nighttime roosts byvarious species of egrets (Egretta spp Bubulcus ibisButorides virescens) and Anhingas (Anhinga anhinga) Fewlive trees were present in the area but in some places therewas significant tall brushy growth There was a mean of125 powerline poles per km on the west side of the roadRoadsides were mowed to a distance of 25 m and treeswere found in less than 1 of roadside edge cover type

1 Email address epearlsufledu2 Present affiliation University of Florida Department ofWildlife Ecology and Conservation Ft Lauderdale Re-search and Education Center 3205 College Ave Davie FL33314 USA

MARCH 2006 SHORT COMMUNICATIONS 81

Sugarcane forms a very dense canopy as it grows andsupports populations of reptiles mammals and birdseither in the field or adjacent habitat During the wintermonths beginning in October sugarcane was burned andthen harvested which attracted large numbers of pre-dators and scavengers The landscape then becamea patchwork of mature fallow harvested and newly-grownsugarcane fields until harvest was completed in earlyspring Rice was grown on less than 10 of the area andprovided flooded habitat for ca 4ndash6 mo of the year fromearly spring to late fall Rice fields were permanentlyflooded and attracted large numbers of waterbirdsespecially during the drawdown of water just prior toharvest usually in July and August (Pearlstine et al 2005)

In contrast the natural areas of the Everglades arecomprised of stretches of sawgrass (Cladium jamaicense)marshes sloughs and wet prairies broken up by flowingopen water and scattered tree islands (Gunderson 1994)Rows of trees no more than a few trees deep stand on theverge at the far edge of the roadside on the east side ofHighway 27 The roadside is bordered by nonnativeAustralian pine (Casuarina sp) trees on 10ndash70 (x 558) of its length Shrubs are present on much of theremaining roadside There are canals on both sides of theroad for about half the distance in Broward County Thecanal on the west side of the road is smaller and flanked byshorter marsh vegetation There are small areas ofintroduced species Melaleuca (Melaleuca quinquenervia)

as well as a local landfill in Broward County Roadside treesoffer natural perch sites primarily dead snags Otherwisethe foliage is very dense and may be suitable only forperching by smaller raptors such as the Red-shoulderedHawk (Buteo lineatus) and American Kestrel (Falco sparver-ius) Like the EAA the view over the marsh is generallyunbroken except where there are stands of trees

Survey Methods We conducted 23 raptorvulturesurveys between October 1998ndashApril 2003 with no surveysin winter 2001ndash02 along a section of Route 27 beginningat Sheridan Street in Pembroke Pines Broward Countyand ending at State Road 80 in South Bay Palm BeachCounty The distance of the road transect was 7648 kmwith 3952 in agriculture and 3696 in natural vegetationtypes

We recorded species activity habitat location andperch type of any raptors observed also recording ageand gender of individuals if possible Because Route 27 isa highway the minimum speed we were able to drive wasca 88 kmhr When a raptor was sighted we stopped thevehicle and recorded location with a GPS receiver andother data if possible In the last 2 yr of the survey the startlocation and time of day of surveys were varied to avoidpotential biases (Bunn et al 1995) We alternated thesurvey start point between the northern end of the routeand the southern end Morning surveys began within anhour of sunrise and ended before noon afternoon surveysbegan shortly after noon and ended before sunset One ortwo observers were present for all surveys On fiveoccasions we recorded large kettles (25) of TurkeyVultures (Cathartes aura) that were attracted to burningfields These observations were not used in the analysesWe recorded the type of perch used by each individualnatural perches included trees brush and dead snags andartificial perches were predominantly powerlines or polesWe also recorded individuals that were flying over roadsidehabitat or flew from perch to perch Species diversity wascalculated for both habitats using proportions as the routelengths varied (Simpson 1949 MacArthur and MacArthur1961) Relative abundance was estimated using an index oftotal number of a species observed divided by totalnumber of km traveled multiplied by 1000 (Woffindenand Murphy 1977) Habitat use in relation to availabilitywas analyzed (using chi-square analysis following Neu et al1974) for linear km of each habitat type

RESULTS

We observed 13 raptor species of which we saw onlyseven in sufficient numbers for analysis six species hadrelative abundances of 50 or fewer than seven observa-tions (Table 1) The species with the greatest index ofrelative abundance (Woffinden and Murphy 1977) werethe American Kestrel and the Turkey Vulture For theseven most common species we found the relativeabundance of raptors in agricultural habitat to average113 individuals per km and in natural habitat to be 061km with an overall mean of 088km There weresignificantly more raptors than expected in agriculturalhabitat compared with natural habitat (x2 5 3874 P

0001 Neu et al 1974) The species richness for each wasequal as all seven of the most common raptors were foundin each landscape Diversity was lower in agricultural than

Table 1 Species observations for each habitat andrelative abundance (birdskm) in parentheses All sevenspecies listed here were used in the analysis of habitat andperch use The number of individuals in each habitat wassignificantly different for the subset of seven species (x2 allP 001)

SPECIES

NUMBER OBSERVED

AGRICULTURE NATURAL TOTAL

American Kestrel(Falco sparverius)

480 (053) 74 (009) 554 (031)

Black Vulture(Coragyps atratus)

11 (001) 85 (010) 96 (005)

Northern Harrier(Circus cyaneus)

49 (005) 4 (00) 53 (003)

Osprey(Pandion haliaetus)

14 (002) 65 (008) 79 (004)

Red-shouldered Hawk(Buteo lineatus)

31 (003) 63 (007) 94 (005)

Red-tailed Hawk(B jamaicensis)

126 (014) 2 (000) 128 (007)

Turkey Vulture(Cathartes aura)

293 (032) 207 (024) 500 (028)

Other speciesa 11 (001) 3 (000) 14 (002)Total 1015 (111) 502 (059) 1517 (086)

a Other species included Bald Eagles (Haliaeetus leucocephalus)Crested Caracaras (Caracara cheriway) Merlins (F columbarius)Peregrine Falcons (F peregrinus) Sharp-shinned Hawks (Accipiter

striatus) and Short-tailed Hawks (B brachyurus)

82 SHORT COMMUNICATIONS VOL 40 NO 1

natural landscapes (066 vs 074 respectively) usingSimpsonrsquos index but higher in agricultural using theShannon-Wiener measure (115 vs 064) and significantlydifferent (t005(2) 75 P 0001) Simpsonrsquos index indicatesthe likelihood that two randomly-chosen individuals willbe different species and tends to emphasize commonspecies (Simpson 1949) The Shannon-Wiener indexmeasures the information content of a sample unit higherdiversity yields higher uncertainty (MacArthur and Mac-Arthur 1961) For all species encountered species richness(number of species) was greatest in agriculture with 12 of13 recorded in these counts Eight of the 13 species weresighted in natural cover types Diversity using bothmeasures discussed above was similar

Four of the species American Kestrel Northern Harrier(Circus cyaneus) Red-tailed Hawk (Buteo jamaicensis) andTurkey Vulture were more abundant in agricultural than

in natural cover types (all P 001) Three species BlackVulture (Coragyps atratus) Osprey (Pandion haliaetus) andRed-shouldered Hawk were observed more frequently innatural cover types than in agricultural areas (all P

001)Bohall and Collopy (1984) also found both Red-

shouldered and Red-tailed hawks in open habitatsHowever in their study these hawks used natural perchesmore than man-made In our study Red-tailed Hawks wereobserved more frequently in agricultural landscapes andRed-shouldered Hawks were observed more frequently innatural habitat Both hawks used powerlines and polesmore often than natural perches (Table 3) Our observa-tions also were in contrast with Preston (1990) who foundthat habitat use was influenced by natural perch availabilityin Red-tailed Hawks Red-tailed Hawks are known to useagricultural areas in high numbers as winter habitat inArkansas (Garner and Bednarz 2000) but were foundmore frequently in natural than agricultural habitat inIdaho (Leptich 1994)

More raptors used powerlinespoles than naturalperches such as brush live trees or snags (P 0001Table 2) In natural and agricultural areas raptorsperched on poles and powerlines with greater frequencythan relative availability would predict Conversely naturalperches were selected less frequently than availabilitywould predict (P 0001 for agriculture and for naturalhabitat) All raptors exhibited significant differences inperch use or flight (Table 3)

DISCUSSION

The greater abundance of raptors in agricultural habitatseemed to reflect species-specific responses to perch typeavailability cover type or both factors in combinationBoth agricultural and natural habitats in this study wereopen and away from the roadsides contained onlysparsely-distributed perches in the form of trees andshrubs

American Kestrels in Florida have demonstrated sexualsegregation by cover type with males tending to occupysites that were more wooded and less open But bothgenders include open habitat in their winter territories(Smallwood 1987 1988) We found kestrels in agriculturalhabitat 87 of the time in this study and they usedpowerlines almost exclusively as perches

Our studies showed that Northern Harriers mostly usedopen areas and included agriculture as part of their winterhabitat (MacWhirter and Bildstein 1996) Only the Ospreyused natural perches in numbers more frequently thanexpected (Table 3)

The two vulture species showed different distributions inrelation to cover types Turkey Vultures seemed to respondpositively to agricultural activities especially harvesting ofsugarcane where they fed on animals killed by harvestactivities and were often seen concentrated in areas ofactive harvest Black Vultures did not respond to harvestactivities and were observed more frequently in natural

Table 3 Locations of individuals by species eitherperched or in flight Locations for each species weresignificantly different than expected

SPECIES

IN

FLIGHT

NATU-

RAL

PERCH

POWERLINE

OR POLE

PERCH OTHER P a

AmericanKestrel 1 18 526 0 0001

BlackVulture 3 18 30 24 0001

NorthernHarrier 10 2 5 0 0004

Osprey 10 47 14 0 0001Red-

shoulderedHawk 5 27 59 2 0001

Red-tailedHawk 0 5 117 2 0001

TurkeyVulture 148 68 7 12 0001

a Determined by chi-square test

Table 2 Number of individuals observed using differentperches All were significantly different (x2 tests P 001)

LOCATION AGRICULTURE NATURAL

BrushtreesnagObservedExpected

7999

1912288

PolepowerlineObservedExpected

6595661

114763

MARCH 2006 SHORT COMMUNICATIONS 83

habitat roosting on a variety of perch types includingAustralian pine bridge structures and radio towers Weobserved several large kettles (10) of Turkey Vultures inthe agricultural areas near harvesting activities BlackVultures on the other hand were usually seen in numbersless than 10 and did not obviously respond to sugarcaneharvests

We used the index of abundance (Woffinden andMurphy 1977) or birds per 1000 km to compare withother studies American Kestrels exhibited higher densitiesin our study than in southwestern New Mexico and Idaho(Eakle et al 1996 Leptich 1994) but were similar to otherFlorida studies (Layne 1980) Red-tailed Hawks were lessabundant in our study area than in Arkansas about thesame as Idaho (but higher in agriculture) and lower thanNew Mexico (Garner and Bednarz 2000 Leptich 1994Eakle et al 1996 respectively) Turkey Vultures were moreabundant than in New Mexico and Northern Harriernumbers were similar to those found in Idaho (Eakle et al1996 Leptich 1994 respectively)

As sugarcane fields are harvested from October throughApril many small animals (rice rats [Oryzomys palustris]marsh rabbits [Sylvilagus palustris] cottontails [S florida-nus] Florida kingsnakes [Lampropeltis getula floridana]leopard frogs [Rana utricularia] and a variety of birds) arecrowded into marginal habitat along canals and roadsThis may provide an artificial concentration of preysources during the harvest season Turkey Vultures areespecially apparent in the area of sugarcane harvest andrespond quickly to the intentional burning of fields (persobs) We also saw Northern Harriers Bald Eagles(Haliaeetus leucocephalus) and Crested Caracaras (Caracaracheriway) at recently-harvested fields

High densities of raptors in agriculture and an apparentselection for artificial perches present in this habitatsuggest that agricultural lands in south Florida mayprovide important habitat for wintering and migratingraptors Because agricultural fields away from roads haveno perches of any kind we have worked with the farmmanager to install tall T-shaped perches in several interiorfields to provide access to more of the landscape bywintering raptors This may also assist in control of rodentsand other agricultural pests

DISTRIBUCION Y ABUNDANCIA RELATIVA DE AVESRAPACES DURANTE EL INVIERNO EN PAISAJESAGRICOLAS Y DE HUMEDALES EN EL SUR DEFLORIDA

RESUMENmdashInvestigamos la distribucion y abundanciarelativa de las aves rapaces entre ambientes agrıcolas ynaturales con base en censos realizados a lo largo de unaautopista de cuatro carriles en el sur de Florida durante losinviernos de 1998ndash2003 sin incluir el de 2001ndash02Registramos la presencia de acuerdo al tipo de coberturael uso de tipos de percha y la densidad de rapaces a lo

largo de la carretera ademas de la riqueza y diversidad deespecies en cada tipo de cobertura Cathartes aura Circuscyaneus Buteo jamaicensis y Falco sparverius fueron masabundantes en los paisajes agrıcolas que en los ambientesnaturales mientras que Coragyps atratus Pandion haliaetus yButeo lineatus fueron registrados con mayor frecuencia enlos ambientes naturales Encontramos un sesgo significa-tivo en el tipo de percha las lıneas electricas y los postesfueron empleados mas frecuentemente que las perchasnaturales Todas las especies fueron observadas con mayorfrecuencia de la esperada en uno o mas de los cinco tiposde percha o al vuelo Las siete especies se encontraron enambos habitats y la diversidad de especies fue general-mente igual entre estos Cada especie parecio exhibirdistintos patrones de uso de habitat y de perchas Nuestrosdatos sugieren que el paisaje agrıcola del sur de Florida esimportante para las poblaciones de rapaces invernantes ymigratorias

[Traduccion del equipo editorial]

ACKNOWLEDGMENTS

This research was supported by the Florida AgriculturalExperiment Station and a grant from the EvergladesAgricultural Area Environmental Protection District andapproved for publication as Journal Series No R-11011We would like to thank B Moser and J Bednarz forassistance with this manuscript

LITERATURE CITED

BOHALL PG AND MW COLLOPY 1984 Seasonal abun-dance habitat use and perch sites of four raptorspecies in north-central Florida J Field Ornithol55181ndash189

BUNN AG W KLEIN AND KL BILDSTEIN 1995 Time-of-dayeffects on the numbers and behavior of non-breedingraptors seen on roadside surveys in eastern Pennsylva-nia J Field Ornithol 66544ndash552

EAKLE WL EL SMITH SW HOFFMAN DW STAHLECKERAND RB DUNCAN 1996 Results of a raptor surveyin southwestern New Mexico J Raptor Res 30183ndash188

FULLER MR AND JA MOSHER 1981 Methods of detectingand counting raptors a review in CJ Ralph and JMScott [EDS] Estimating numbers of terrestrial birdsStud Avian Biol 6235ndash246

GARNER HD AND JC BEDNARZ 2000 Habitat use by Red-tailed Hawks wintering in the delta region of ArkansasJ Raptor Res 3426ndash32

GUNDERSON LH 1994 Vegetation of the EvergladesDeterminants of Community Composition in SMDavis and JC Ogden [EDS] Everglades the ecosystemand its restoration St Lucie Press Delray Beach FLUSA

IZUNO FT CA SANCHEZ FJ COALE AB BOTTCHER AND

DB JONES 1991 Phosphorus concentrations in drain-age water in the Everglades agricultural area J EnvironQual 20608ndash619

84 SHORT COMMUNICATIONS VOL 40 NO 1

LAYNE JN 1980 Trends in numbers of American Kestrelson roadside counts in southcentral Florida from 1968to 1976 Florida Field Nat 81ndash36

LEPTICH DJ 1994 Agricultural development and itsinfluence on raptors in southern Idaho Northwest Sci68167ndash171

LEYHE JE AND G RITCHISON 2004 Perch sites and huntingbehavior of Red-tailed Hawks (Buteo jamaicensis) J

Raptor Res 3819ndash25LIGHT SS AND JW DINEEN 1994 Water control in the

Everglades a historical perspective in SM Davis andJC Ogden [EDS] Everglades the ecosystem and itsrestoration St Lucie Press Delray Beach FL USA

MACARTHUR RH AND JW MACARTHUR 1961 On birdspecies diversity Ecology 42594ndash598

MACWHIRTER RB AND KL BILDSTEIN 1996 NorthernHarrier (Circus cyaneus) In A Poole and F Gill [EDS]The birds of North America No 210 The Academy ofNatural Sciences Philadelphia PA USA and TheAmerican Ornithologistsrsquo Union Washington DC USA

MEUNIER FD C VERHEYDEN AND P JOUVENTIN 2000 Use ofroadsides by diurnal raptors in agricultural landscapesBiol Conserv 92291ndash298

MILLSAP BA AND MN LEFRANC JR 1988 Road transectcounts for raptors how reliable are they J Raptor Res228ndash16

NEU CW CR BYERS AND JM PEEK 1974 A technique foranalysis of utilization-availability data J Wildl Manage38541ndash545

PEARLSTINE EV ML CASLER AND FJ MAZZOTTI 2005 Achecklist of birds of the Everglades agricultural areaFlorida Sci 6884ndash96

PEARLSTINE L S SMITH AND WM KITCHENS 2001 TheFlorida Gap Analysis Final Report USGS TechnicalReport 65 Published by National GAP ProgramMoscow ID USA

PORTER JW AND KG PORTER 2002 IntroductionThe Everglades Florida Bay and coral reefs of theFlorida Keys an ecosystem sourcebook in JW Porterand KG Porter [EDS] The Everglades Florida Bayand coral reefs of the Florida Keys an ecosystemsourcebook CRC Press Boca Raton FL USA

PRESTON CR 1990 Distribution of raptor foraging inrelation to prey biomass and habitat structure Condor92107ndash112

SIMPSON EH 1949 Measurement of diversity Nature163688

SMALLWOOD JA 1987 Sexual segregation by habitat inAmerican Kestrels wintering in southcentral Floridavegetative structure and responses to differential preyavailability Condor 89842ndash849

mdashmdashmdash 1988 A mechanism of sexual segregation byhabitat in American Kestrels (Falco sparverius) winteringin south-central Florida Auk 10536ndash46

SMALLWOOD SK BJ NAKAMOTO AND S GENG 1996Association analysis of raptors on a farming landscapePages 177ndash190 in DM Bird DE Varland and JJNegro [EDS] Raptors in human landscapes AcademicPress London UK

SORLEY CS AND DE ANDERSON 1994 Raptor abundance insouth-central Kenya in relation to land-use patternsAfr J Ecol 3230ndash38

THIOLLAY J-M AND Z RAHMAN 2002 The raptor commu-nity of central Sulawesi habitat selection and conser-vation status Biol Conserv 107111ndash122

WOFFINDEN ND AND JR MURPHY 1977 A roadside raptorcensus in the eastern Great Basin 1973ndash74 Raptor Res1162ndash66

ZAR JH 1984 Biostatistical Analysis Prentice Hall UpperSaddle River NJ USA

Received 12 January 2004 accepted 17 October 2005

MARCH 2006 SHORT COMMUNICATIONS 85

Sugarcane forms a very dense canopy as it grows andsupports populations of reptiles mammals and birdseither in the field or adjacent habitat During the wintermonths beginning in October sugarcane was burned andthen harvested which attracted large numbers of pre-dators and scavengers The landscape then becamea patchwork of mature fallow harvested and newly-grownsugarcane fields until harvest was completed in earlyspring Rice was grown on less than 10 of the area andprovided flooded habitat for ca 4ndash6 mo of the year fromearly spring to late fall Rice fields were permanentlyflooded and attracted large numbers of waterbirdsespecially during the drawdown of water just prior toharvest usually in July and August (Pearlstine et al 2005)

In contrast the natural areas of the Everglades arecomprised of stretches of sawgrass (Cladium jamaicense)marshes sloughs and wet prairies broken up by flowingopen water and scattered tree islands (Gunderson 1994)Rows of trees no more than a few trees deep stand on theverge at the far edge of the roadside on the east side ofHighway 27 The roadside is bordered by nonnativeAustralian pine (Casuarina sp) trees on 10ndash70 (x 558) of its length Shrubs are present on much of theremaining roadside There are canals on both sides of theroad for about half the distance in Broward County Thecanal on the west side of the road is smaller and flanked byshorter marsh vegetation There are small areas ofintroduced species Melaleuca (Melaleuca quinquenervia)

as well as a local landfill in Broward County Roadside treesoffer natural perch sites primarily dead snags Otherwisethe foliage is very dense and may be suitable only forperching by smaller raptors such as the Red-shoulderedHawk (Buteo lineatus) and American Kestrel (Falco sparver-ius) Like the EAA the view over the marsh is generallyunbroken except where there are stands of trees

Survey Methods We conducted 23 raptorvulturesurveys between October 1998ndashApril 2003 with no surveysin winter 2001ndash02 along a section of Route 27 beginningat Sheridan Street in Pembroke Pines Broward Countyand ending at State Road 80 in South Bay Palm BeachCounty The distance of the road transect was 7648 kmwith 3952 in agriculture and 3696 in natural vegetationtypes

We recorded species activity habitat location andperch type of any raptors observed also recording ageand gender of individuals if possible Because Route 27 isa highway the minimum speed we were able to drive wasca 88 kmhr When a raptor was sighted we stopped thevehicle and recorded location with a GPS receiver andother data if possible In the last 2 yr of the survey the startlocation and time of day of surveys were varied to avoidpotential biases (Bunn et al 1995) We alternated thesurvey start point between the northern end of the routeand the southern end Morning surveys began within anhour of sunrise and ended before noon afternoon surveysbegan shortly after noon and ended before sunset One ortwo observers were present for all surveys On fiveoccasions we recorded large kettles (25) of TurkeyVultures (Cathartes aura) that were attracted to burningfields These observations were not used in the analysesWe recorded the type of perch used by each individualnatural perches included trees brush and dead snags andartificial perches were predominantly powerlines or polesWe also recorded individuals that were flying over roadsidehabitat or flew from perch to perch Species diversity wascalculated for both habitats using proportions as the routelengths varied (Simpson 1949 MacArthur and MacArthur1961) Relative abundance was estimated using an index oftotal number of a species observed divided by totalnumber of km traveled multiplied by 1000 (Woffindenand Murphy 1977) Habitat use in relation to availabilitywas analyzed (using chi-square analysis following Neu et al1974) for linear km of each habitat type

RESULTS

We observed 13 raptor species of which we saw onlyseven in sufficient numbers for analysis six species hadrelative abundances of 50 or fewer than seven observa-tions (Table 1) The species with the greatest index ofrelative abundance (Woffinden and Murphy 1977) werethe American Kestrel and the Turkey Vulture For theseven most common species we found the relativeabundance of raptors in agricultural habitat to average113 individuals per km and in natural habitat to be 061km with an overall mean of 088km There weresignificantly more raptors than expected in agriculturalhabitat compared with natural habitat (x2 5 3874 P

0001 Neu et al 1974) The species richness for each wasequal as all seven of the most common raptors were foundin each landscape Diversity was lower in agricultural than

Table 1 Species observations for each habitat andrelative abundance (birdskm) in parentheses All sevenspecies listed here were used in the analysis of habitat andperch use The number of individuals in each habitat wassignificantly different for the subset of seven species (x2 allP 001)

SPECIES

NUMBER OBSERVED

AGRICULTURE NATURAL TOTAL

American Kestrel(Falco sparverius)

480 (053) 74 (009) 554 (031)

Black Vulture(Coragyps atratus)

11 (001) 85 (010) 96 (005)

Northern Harrier(Circus cyaneus)

49 (005) 4 (00) 53 (003)

Osprey(Pandion haliaetus)

14 (002) 65 (008) 79 (004)

Red-shouldered Hawk(Buteo lineatus)

31 (003) 63 (007) 94 (005)

Red-tailed Hawk(B jamaicensis)

126 (014) 2 (000) 128 (007)

Turkey Vulture(Cathartes aura)

293 (032) 207 (024) 500 (028)

Other speciesa 11 (001) 3 (000) 14 (002)Total 1015 (111) 502 (059) 1517 (086)

a Other species included Bald Eagles (Haliaeetus leucocephalus)Crested Caracaras (Caracara cheriway) Merlins (F columbarius)Peregrine Falcons (F peregrinus) Sharp-shinned Hawks (Accipiter

striatus) and Short-tailed Hawks (B brachyurus)

82 SHORT COMMUNICATIONS VOL 40 NO 1

natural landscapes (066 vs 074 respectively) usingSimpsonrsquos index but higher in agricultural using theShannon-Wiener measure (115 vs 064) and significantlydifferent (t005(2) 75 P 0001) Simpsonrsquos index indicatesthe likelihood that two randomly-chosen individuals willbe different species and tends to emphasize commonspecies (Simpson 1949) The Shannon-Wiener indexmeasures the information content of a sample unit higherdiversity yields higher uncertainty (MacArthur and Mac-Arthur 1961) For all species encountered species richness(number of species) was greatest in agriculture with 12 of13 recorded in these counts Eight of the 13 species weresighted in natural cover types Diversity using bothmeasures discussed above was similar

Four of the species American Kestrel Northern Harrier(Circus cyaneus) Red-tailed Hawk (Buteo jamaicensis) andTurkey Vulture were more abundant in agricultural than

in natural cover types (all P 001) Three species BlackVulture (Coragyps atratus) Osprey (Pandion haliaetus) andRed-shouldered Hawk were observed more frequently innatural cover types than in agricultural areas (all P

001)Bohall and Collopy (1984) also found both Red-

shouldered and Red-tailed hawks in open habitatsHowever in their study these hawks used natural perchesmore than man-made In our study Red-tailed Hawks wereobserved more frequently in agricultural landscapes andRed-shouldered Hawks were observed more frequently innatural habitat Both hawks used powerlines and polesmore often than natural perches (Table 3) Our observa-tions also were in contrast with Preston (1990) who foundthat habitat use was influenced by natural perch availabilityin Red-tailed Hawks Red-tailed Hawks are known to useagricultural areas in high numbers as winter habitat inArkansas (Garner and Bednarz 2000) but were foundmore frequently in natural than agricultural habitat inIdaho (Leptich 1994)

More raptors used powerlinespoles than naturalperches such as brush live trees or snags (P 0001Table 2) In natural and agricultural areas raptorsperched on poles and powerlines with greater frequencythan relative availability would predict Conversely naturalperches were selected less frequently than availabilitywould predict (P 0001 for agriculture and for naturalhabitat) All raptors exhibited significant differences inperch use or flight (Table 3)

DISCUSSION

The greater abundance of raptors in agricultural habitatseemed to reflect species-specific responses to perch typeavailability cover type or both factors in combinationBoth agricultural and natural habitats in this study wereopen and away from the roadsides contained onlysparsely-distributed perches in the form of trees andshrubs

American Kestrels in Florida have demonstrated sexualsegregation by cover type with males tending to occupysites that were more wooded and less open But bothgenders include open habitat in their winter territories(Smallwood 1987 1988) We found kestrels in agriculturalhabitat 87 of the time in this study and they usedpowerlines almost exclusively as perches

Our studies showed that Northern Harriers mostly usedopen areas and included agriculture as part of their winterhabitat (MacWhirter and Bildstein 1996) Only the Ospreyused natural perches in numbers more frequently thanexpected (Table 3)

The two vulture species showed different distributions inrelation to cover types Turkey Vultures seemed to respondpositively to agricultural activities especially harvesting ofsugarcane where they fed on animals killed by harvestactivities and were often seen concentrated in areas ofactive harvest Black Vultures did not respond to harvestactivities and were observed more frequently in natural

Table 3 Locations of individuals by species eitherperched or in flight Locations for each species weresignificantly different than expected

SPECIES

IN

FLIGHT

NATU-

RAL

PERCH

POWERLINE

OR POLE

PERCH OTHER P a

AmericanKestrel 1 18 526 0 0001

BlackVulture 3 18 30 24 0001

NorthernHarrier 10 2 5 0 0004

Osprey 10 47 14 0 0001Red-

shoulderedHawk 5 27 59 2 0001

Red-tailedHawk 0 5 117 2 0001

TurkeyVulture 148 68 7 12 0001

a Determined by chi-square test

Table 2 Number of individuals observed using differentperches All were significantly different (x2 tests P 001)

LOCATION AGRICULTURE NATURAL

BrushtreesnagObservedExpected

7999

1912288

PolepowerlineObservedExpected

6595661

114763

MARCH 2006 SHORT COMMUNICATIONS 83

habitat roosting on a variety of perch types includingAustralian pine bridge structures and radio towers Weobserved several large kettles (10) of Turkey Vultures inthe agricultural areas near harvesting activities BlackVultures on the other hand were usually seen in numbersless than 10 and did not obviously respond to sugarcaneharvests

We used the index of abundance (Woffinden andMurphy 1977) or birds per 1000 km to compare withother studies American Kestrels exhibited higher densitiesin our study than in southwestern New Mexico and Idaho(Eakle et al 1996 Leptich 1994) but were similar to otherFlorida studies (Layne 1980) Red-tailed Hawks were lessabundant in our study area than in Arkansas about thesame as Idaho (but higher in agriculture) and lower thanNew Mexico (Garner and Bednarz 2000 Leptich 1994Eakle et al 1996 respectively) Turkey Vultures were moreabundant than in New Mexico and Northern Harriernumbers were similar to those found in Idaho (Eakle et al1996 Leptich 1994 respectively)

As sugarcane fields are harvested from October throughApril many small animals (rice rats [Oryzomys palustris]marsh rabbits [Sylvilagus palustris] cottontails [S florida-nus] Florida kingsnakes [Lampropeltis getula floridana]leopard frogs [Rana utricularia] and a variety of birds) arecrowded into marginal habitat along canals and roadsThis may provide an artificial concentration of preysources during the harvest season Turkey Vultures areespecially apparent in the area of sugarcane harvest andrespond quickly to the intentional burning of fields (persobs) We also saw Northern Harriers Bald Eagles(Haliaeetus leucocephalus) and Crested Caracaras (Caracaracheriway) at recently-harvested fields

High densities of raptors in agriculture and an apparentselection for artificial perches present in this habitatsuggest that agricultural lands in south Florida mayprovide important habitat for wintering and migratingraptors Because agricultural fields away from roads haveno perches of any kind we have worked with the farmmanager to install tall T-shaped perches in several interiorfields to provide access to more of the landscape bywintering raptors This may also assist in control of rodentsand other agricultural pests

DISTRIBUCION Y ABUNDANCIA RELATIVA DE AVESRAPACES DURANTE EL INVIERNO EN PAISAJESAGRICOLAS Y DE HUMEDALES EN EL SUR DEFLORIDA

RESUMENmdashInvestigamos la distribucion y abundanciarelativa de las aves rapaces entre ambientes agrıcolas ynaturales con base en censos realizados a lo largo de unaautopista de cuatro carriles en el sur de Florida durante losinviernos de 1998ndash2003 sin incluir el de 2001ndash02Registramos la presencia de acuerdo al tipo de coberturael uso de tipos de percha y la densidad de rapaces a lo

largo de la carretera ademas de la riqueza y diversidad deespecies en cada tipo de cobertura Cathartes aura Circuscyaneus Buteo jamaicensis y Falco sparverius fueron masabundantes en los paisajes agrıcolas que en los ambientesnaturales mientras que Coragyps atratus Pandion haliaetus yButeo lineatus fueron registrados con mayor frecuencia enlos ambientes naturales Encontramos un sesgo significa-tivo en el tipo de percha las lıneas electricas y los postesfueron empleados mas frecuentemente que las perchasnaturales Todas las especies fueron observadas con mayorfrecuencia de la esperada en uno o mas de los cinco tiposde percha o al vuelo Las siete especies se encontraron enambos habitats y la diversidad de especies fue general-mente igual entre estos Cada especie parecio exhibirdistintos patrones de uso de habitat y de perchas Nuestrosdatos sugieren que el paisaje agrıcola del sur de Florida esimportante para las poblaciones de rapaces invernantes ymigratorias

[Traduccion del equipo editorial]

ACKNOWLEDGMENTS

This research was supported by the Florida AgriculturalExperiment Station and a grant from the EvergladesAgricultural Area Environmental Protection District andapproved for publication as Journal Series No R-11011We would like to thank B Moser and J Bednarz forassistance with this manuscript

LITERATURE CITED

BOHALL PG AND MW COLLOPY 1984 Seasonal abun-dance habitat use and perch sites of four raptorspecies in north-central Florida J Field Ornithol55181ndash189

BUNN AG W KLEIN AND KL BILDSTEIN 1995 Time-of-dayeffects on the numbers and behavior of non-breedingraptors seen on roadside surveys in eastern Pennsylva-nia J Field Ornithol 66544ndash552

EAKLE WL EL SMITH SW HOFFMAN DW STAHLECKERAND RB DUNCAN 1996 Results of a raptor surveyin southwestern New Mexico J Raptor Res 30183ndash188

FULLER MR AND JA MOSHER 1981 Methods of detectingand counting raptors a review in CJ Ralph and JMScott [EDS] Estimating numbers of terrestrial birdsStud Avian Biol 6235ndash246

GARNER HD AND JC BEDNARZ 2000 Habitat use by Red-tailed Hawks wintering in the delta region of ArkansasJ Raptor Res 3426ndash32

GUNDERSON LH 1994 Vegetation of the EvergladesDeterminants of Community Composition in SMDavis and JC Ogden [EDS] Everglades the ecosystemand its restoration St Lucie Press Delray Beach FLUSA

IZUNO FT CA SANCHEZ FJ COALE AB BOTTCHER AND

DB JONES 1991 Phosphorus concentrations in drain-age water in the Everglades agricultural area J EnvironQual 20608ndash619

84 SHORT COMMUNICATIONS VOL 40 NO 1

LAYNE JN 1980 Trends in numbers of American Kestrelson roadside counts in southcentral Florida from 1968to 1976 Florida Field Nat 81ndash36

LEPTICH DJ 1994 Agricultural development and itsinfluence on raptors in southern Idaho Northwest Sci68167ndash171

LEYHE JE AND G RITCHISON 2004 Perch sites and huntingbehavior of Red-tailed Hawks (Buteo jamaicensis) J

Raptor Res 3819ndash25LIGHT SS AND JW DINEEN 1994 Water control in the

Everglades a historical perspective in SM Davis andJC Ogden [EDS] Everglades the ecosystem and itsrestoration St Lucie Press Delray Beach FL USA

MACARTHUR RH AND JW MACARTHUR 1961 On birdspecies diversity Ecology 42594ndash598

MACWHIRTER RB AND KL BILDSTEIN 1996 NorthernHarrier (Circus cyaneus) In A Poole and F Gill [EDS]The birds of North America No 210 The Academy ofNatural Sciences Philadelphia PA USA and TheAmerican Ornithologistsrsquo Union Washington DC USA

MEUNIER FD C VERHEYDEN AND P JOUVENTIN 2000 Use ofroadsides by diurnal raptors in agricultural landscapesBiol Conserv 92291ndash298

MILLSAP BA AND MN LEFRANC JR 1988 Road transectcounts for raptors how reliable are they J Raptor Res228ndash16

NEU CW CR BYERS AND JM PEEK 1974 A technique foranalysis of utilization-availability data J Wildl Manage38541ndash545

PEARLSTINE EV ML CASLER AND FJ MAZZOTTI 2005 Achecklist of birds of the Everglades agricultural areaFlorida Sci 6884ndash96

PEARLSTINE L S SMITH AND WM KITCHENS 2001 TheFlorida Gap Analysis Final Report USGS TechnicalReport 65 Published by National GAP ProgramMoscow ID USA

PORTER JW AND KG PORTER 2002 IntroductionThe Everglades Florida Bay and coral reefs of theFlorida Keys an ecosystem sourcebook in JW Porterand KG Porter [EDS] The Everglades Florida Bayand coral reefs of the Florida Keys an ecosystemsourcebook CRC Press Boca Raton FL USA

PRESTON CR 1990 Distribution of raptor foraging inrelation to prey biomass and habitat structure Condor92107ndash112

SIMPSON EH 1949 Measurement of diversity Nature163688

SMALLWOOD JA 1987 Sexual segregation by habitat inAmerican Kestrels wintering in southcentral Floridavegetative structure and responses to differential preyavailability Condor 89842ndash849

mdashmdashmdash 1988 A mechanism of sexual segregation byhabitat in American Kestrels (Falco sparverius) winteringin south-central Florida Auk 10536ndash46

SMALLWOOD SK BJ NAKAMOTO AND S GENG 1996Association analysis of raptors on a farming landscapePages 177ndash190 in DM Bird DE Varland and JJNegro [EDS] Raptors in human landscapes AcademicPress London UK

SORLEY CS AND DE ANDERSON 1994 Raptor abundance insouth-central Kenya in relation to land-use patternsAfr J Ecol 3230ndash38

THIOLLAY J-M AND Z RAHMAN 2002 The raptor commu-nity of central Sulawesi habitat selection and conser-vation status Biol Conserv 107111ndash122

WOFFINDEN ND AND JR MURPHY 1977 A roadside raptorcensus in the eastern Great Basin 1973ndash74 Raptor Res1162ndash66

ZAR JH 1984 Biostatistical Analysis Prentice Hall UpperSaddle River NJ USA

Received 12 January 2004 accepted 17 October 2005

MARCH 2006 SHORT COMMUNICATIONS 85

natural landscapes (066 vs 074 respectively) usingSimpsonrsquos index but higher in agricultural using theShannon-Wiener measure (115 vs 064) and significantlydifferent (t005(2) 75 P 0001) Simpsonrsquos index indicatesthe likelihood that two randomly-chosen individuals willbe different species and tends to emphasize commonspecies (Simpson 1949) The Shannon-Wiener indexmeasures the information content of a sample unit higherdiversity yields higher uncertainty (MacArthur and Mac-Arthur 1961) For all species encountered species richness(number of species) was greatest in agriculture with 12 of13 recorded in these counts Eight of the 13 species weresighted in natural cover types Diversity using bothmeasures discussed above was similar

Four of the species American Kestrel Northern Harrier(Circus cyaneus) Red-tailed Hawk (Buteo jamaicensis) andTurkey Vulture were more abundant in agricultural than

in natural cover types (all P 001) Three species BlackVulture (Coragyps atratus) Osprey (Pandion haliaetus) andRed-shouldered Hawk were observed more frequently innatural cover types than in agricultural areas (all P

001)Bohall and Collopy (1984) also found both Red-

shouldered and Red-tailed hawks in open habitatsHowever in their study these hawks used natural perchesmore than man-made In our study Red-tailed Hawks wereobserved more frequently in agricultural landscapes andRed-shouldered Hawks were observed more frequently innatural habitat Both hawks used powerlines and polesmore often than natural perches (Table 3) Our observa-tions also were in contrast with Preston (1990) who foundthat habitat use was influenced by natural perch availabilityin Red-tailed Hawks Red-tailed Hawks are known to useagricultural areas in high numbers as winter habitat inArkansas (Garner and Bednarz 2000) but were foundmore frequently in natural than agricultural habitat inIdaho (Leptich 1994)

More raptors used powerlinespoles than naturalperches such as brush live trees or snags (P 0001Table 2) In natural and agricultural areas raptorsperched on poles and powerlines with greater frequencythan relative availability would predict Conversely naturalperches were selected less frequently than availabilitywould predict (P 0001 for agriculture and for naturalhabitat) All raptors exhibited significant differences inperch use or flight (Table 3)

DISCUSSION

The greater abundance of raptors in agricultural habitatseemed to reflect species-specific responses to perch typeavailability cover type or both factors in combinationBoth agricultural and natural habitats in this study wereopen and away from the roadsides contained onlysparsely-distributed perches in the form of trees andshrubs

American Kestrels in Florida have demonstrated sexualsegregation by cover type with males tending to occupysites that were more wooded and less open But bothgenders include open habitat in their winter territories(Smallwood 1987 1988) We found kestrels in agriculturalhabitat 87 of the time in this study and they usedpowerlines almost exclusively as perches

Our studies showed that Northern Harriers mostly usedopen areas and included agriculture as part of their winterhabitat (MacWhirter and Bildstein 1996) Only the Ospreyused natural perches in numbers more frequently thanexpected (Table 3)

The two vulture species showed different distributions inrelation to cover types Turkey Vultures seemed to respondpositively to agricultural activities especially harvesting ofsugarcane where they fed on animals killed by harvestactivities and were often seen concentrated in areas ofactive harvest Black Vultures did not respond to harvestactivities and were observed more frequently in natural

Table 3 Locations of individuals by species eitherperched or in flight Locations for each species weresignificantly different than expected

SPECIES

IN

FLIGHT

NATU-

RAL

PERCH

POWERLINE

OR POLE

PERCH OTHER P a

AmericanKestrel 1 18 526 0 0001

BlackVulture 3 18 30 24 0001

NorthernHarrier 10 2 5 0 0004

Osprey 10 47 14 0 0001Red-

shoulderedHawk 5 27 59 2 0001

Red-tailedHawk 0 5 117 2 0001

TurkeyVulture 148 68 7 12 0001

a Determined by chi-square test

Table 2 Number of individuals observed using differentperches All were significantly different (x2 tests P 001)

LOCATION AGRICULTURE NATURAL

BrushtreesnagObservedExpected

7999

1912288

PolepowerlineObservedExpected

6595661

114763

MARCH 2006 SHORT COMMUNICATIONS 83

habitat roosting on a variety of perch types includingAustralian pine bridge structures and radio towers Weobserved several large kettles (10) of Turkey Vultures inthe agricultural areas near harvesting activities BlackVultures on the other hand were usually seen in numbersless than 10 and did not obviously respond to sugarcaneharvests

We used the index of abundance (Woffinden andMurphy 1977) or birds per 1000 km to compare withother studies American Kestrels exhibited higher densitiesin our study than in southwestern New Mexico and Idaho(Eakle et al 1996 Leptich 1994) but were similar to otherFlorida studies (Layne 1980) Red-tailed Hawks were lessabundant in our study area than in Arkansas about thesame as Idaho (but higher in agriculture) and lower thanNew Mexico (Garner and Bednarz 2000 Leptich 1994Eakle et al 1996 respectively) Turkey Vultures were moreabundant than in New Mexico and Northern Harriernumbers were similar to those found in Idaho (Eakle et al1996 Leptich 1994 respectively)

As sugarcane fields are harvested from October throughApril many small animals (rice rats [Oryzomys palustris]marsh rabbits [Sylvilagus palustris] cottontails [S florida-nus] Florida kingsnakes [Lampropeltis getula floridana]leopard frogs [Rana utricularia] and a variety of birds) arecrowded into marginal habitat along canals and roadsThis may provide an artificial concentration of preysources during the harvest season Turkey Vultures areespecially apparent in the area of sugarcane harvest andrespond quickly to the intentional burning of fields (persobs) We also saw Northern Harriers Bald Eagles(Haliaeetus leucocephalus) and Crested Caracaras (Caracaracheriway) at recently-harvested fields

High densities of raptors in agriculture and an apparentselection for artificial perches present in this habitatsuggest that agricultural lands in south Florida mayprovide important habitat for wintering and migratingraptors Because agricultural fields away from roads haveno perches of any kind we have worked with the farmmanager to install tall T-shaped perches in several interiorfields to provide access to more of the landscape bywintering raptors This may also assist in control of rodentsand other agricultural pests

DISTRIBUCION Y ABUNDANCIA RELATIVA DE AVESRAPACES DURANTE EL INVIERNO EN PAISAJESAGRICOLAS Y DE HUMEDALES EN EL SUR DEFLORIDA

RESUMENmdashInvestigamos la distribucion y abundanciarelativa de las aves rapaces entre ambientes agrıcolas ynaturales con base en censos realizados a lo largo de unaautopista de cuatro carriles en el sur de Florida durante losinviernos de 1998ndash2003 sin incluir el de 2001ndash02Registramos la presencia de acuerdo al tipo de coberturael uso de tipos de percha y la densidad de rapaces a lo

largo de la carretera ademas de la riqueza y diversidad deespecies en cada tipo de cobertura Cathartes aura Circuscyaneus Buteo jamaicensis y Falco sparverius fueron masabundantes en los paisajes agrıcolas que en los ambientesnaturales mientras que Coragyps atratus Pandion haliaetus yButeo lineatus fueron registrados con mayor frecuencia enlos ambientes naturales Encontramos un sesgo significa-tivo en el tipo de percha las lıneas electricas y los postesfueron empleados mas frecuentemente que las perchasnaturales Todas las especies fueron observadas con mayorfrecuencia de la esperada en uno o mas de los cinco tiposde percha o al vuelo Las siete especies se encontraron enambos habitats y la diversidad de especies fue general-mente igual entre estos Cada especie parecio exhibirdistintos patrones de uso de habitat y de perchas Nuestrosdatos sugieren que el paisaje agrıcola del sur de Florida esimportante para las poblaciones de rapaces invernantes ymigratorias

[Traduccion del equipo editorial]

ACKNOWLEDGMENTS

This research was supported by the Florida AgriculturalExperiment Station and a grant from the EvergladesAgricultural Area Environmental Protection District andapproved for publication as Journal Series No R-11011We would like to thank B Moser and J Bednarz forassistance with this manuscript

LITERATURE CITED

BOHALL PG AND MW COLLOPY 1984 Seasonal abun-dance habitat use and perch sites of four raptorspecies in north-central Florida J Field Ornithol55181ndash189

BUNN AG W KLEIN AND KL BILDSTEIN 1995 Time-of-dayeffects on the numbers and behavior of non-breedingraptors seen on roadside surveys in eastern Pennsylva-nia J Field Ornithol 66544ndash552

EAKLE WL EL SMITH SW HOFFMAN DW STAHLECKERAND RB DUNCAN 1996 Results of a raptor surveyin southwestern New Mexico J Raptor Res 30183ndash188

FULLER MR AND JA MOSHER 1981 Methods of detectingand counting raptors a review in CJ Ralph and JMScott [EDS] Estimating numbers of terrestrial birdsStud Avian Biol 6235ndash246

GARNER HD AND JC BEDNARZ 2000 Habitat use by Red-tailed Hawks wintering in the delta region of ArkansasJ Raptor Res 3426ndash32

GUNDERSON LH 1994 Vegetation of the EvergladesDeterminants of Community Composition in SMDavis and JC Ogden [EDS] Everglades the ecosystemand its restoration St Lucie Press Delray Beach FLUSA

IZUNO FT CA SANCHEZ FJ COALE AB BOTTCHER AND

DB JONES 1991 Phosphorus concentrations in drain-age water in the Everglades agricultural area J EnvironQual 20608ndash619

84 SHORT COMMUNICATIONS VOL 40 NO 1

LAYNE JN 1980 Trends in numbers of American Kestrelson roadside counts in southcentral Florida from 1968to 1976 Florida Field Nat 81ndash36

LEPTICH DJ 1994 Agricultural development and itsinfluence on raptors in southern Idaho Northwest Sci68167ndash171

LEYHE JE AND G RITCHISON 2004 Perch sites and huntingbehavior of Red-tailed Hawks (Buteo jamaicensis) J

Raptor Res 3819ndash25LIGHT SS AND JW DINEEN 1994 Water control in the

Everglades a historical perspective in SM Davis andJC Ogden [EDS] Everglades the ecosystem and itsrestoration St Lucie Press Delray Beach FL USA

MACARTHUR RH AND JW MACARTHUR 1961 On birdspecies diversity Ecology 42594ndash598

MACWHIRTER RB AND KL BILDSTEIN 1996 NorthernHarrier (Circus cyaneus) In A Poole and F Gill [EDS]The birds of North America No 210 The Academy ofNatural Sciences Philadelphia PA USA and TheAmerican Ornithologistsrsquo Union Washington DC USA

MEUNIER FD C VERHEYDEN AND P JOUVENTIN 2000 Use ofroadsides by diurnal raptors in agricultural landscapesBiol Conserv 92291ndash298

MILLSAP BA AND MN LEFRANC JR 1988 Road transectcounts for raptors how reliable are they J Raptor Res228ndash16

NEU CW CR BYERS AND JM PEEK 1974 A technique foranalysis of utilization-availability data J Wildl Manage38541ndash545

PEARLSTINE EV ML CASLER AND FJ MAZZOTTI 2005 Achecklist of birds of the Everglades agricultural areaFlorida Sci 6884ndash96

PEARLSTINE L S SMITH AND WM KITCHENS 2001 TheFlorida Gap Analysis Final Report USGS TechnicalReport 65 Published by National GAP ProgramMoscow ID USA

PORTER JW AND KG PORTER 2002 IntroductionThe Everglades Florida Bay and coral reefs of theFlorida Keys an ecosystem sourcebook in JW Porterand KG Porter [EDS] The Everglades Florida Bayand coral reefs of the Florida Keys an ecosystemsourcebook CRC Press Boca Raton FL USA

PRESTON CR 1990 Distribution of raptor foraging inrelation to prey biomass and habitat structure Condor92107ndash112

SIMPSON EH 1949 Measurement of diversity Nature163688

SMALLWOOD JA 1987 Sexual segregation by habitat inAmerican Kestrels wintering in southcentral Floridavegetative structure and responses to differential preyavailability Condor 89842ndash849

mdashmdashmdash 1988 A mechanism of sexual segregation byhabitat in American Kestrels (Falco sparverius) winteringin south-central Florida Auk 10536ndash46

SMALLWOOD SK BJ NAKAMOTO AND S GENG 1996Association analysis of raptors on a farming landscapePages 177ndash190 in DM Bird DE Varland and JJNegro [EDS] Raptors in human landscapes AcademicPress London UK

SORLEY CS AND DE ANDERSON 1994 Raptor abundance insouth-central Kenya in relation to land-use patternsAfr J Ecol 3230ndash38

THIOLLAY J-M AND Z RAHMAN 2002 The raptor commu-nity of central Sulawesi habitat selection and conser-vation status Biol Conserv 107111ndash122

WOFFINDEN ND AND JR MURPHY 1977 A roadside raptorcensus in the eastern Great Basin 1973ndash74 Raptor Res1162ndash66

ZAR JH 1984 Biostatistical Analysis Prentice Hall UpperSaddle River NJ USA

Received 12 January 2004 accepted 17 October 2005

MARCH 2006 SHORT COMMUNICATIONS 85

habitat roosting on a variety of perch types includingAustralian pine bridge structures and radio towers Weobserved several large kettles (10) of Turkey Vultures inthe agricultural areas near harvesting activities BlackVultures on the other hand were usually seen in numbersless than 10 and did not obviously respond to sugarcaneharvests

We used the index of abundance (Woffinden andMurphy 1977) or birds per 1000 km to compare withother studies American Kestrels exhibited higher densitiesin our study than in southwestern New Mexico and Idaho(Eakle et al 1996 Leptich 1994) but were similar to otherFlorida studies (Layne 1980) Red-tailed Hawks were lessabundant in our study area than in Arkansas about thesame as Idaho (but higher in agriculture) and lower thanNew Mexico (Garner and Bednarz 2000 Leptich 1994Eakle et al 1996 respectively) Turkey Vultures were moreabundant than in New Mexico and Northern Harriernumbers were similar to those found in Idaho (Eakle et al1996 Leptich 1994 respectively)

As sugarcane fields are harvested from October throughApril many small animals (rice rats [Oryzomys palustris]marsh rabbits [Sylvilagus palustris] cottontails [S florida-nus] Florida kingsnakes [Lampropeltis getula floridana]leopard frogs [Rana utricularia] and a variety of birds) arecrowded into marginal habitat along canals and roadsThis may provide an artificial concentration of preysources during the harvest season Turkey Vultures areespecially apparent in the area of sugarcane harvest andrespond quickly to the intentional burning of fields (persobs) We also saw Northern Harriers Bald Eagles(Haliaeetus leucocephalus) and Crested Caracaras (Caracaracheriway) at recently-harvested fields

High densities of raptors in agriculture and an apparentselection for artificial perches present in this habitatsuggest that agricultural lands in south Florida mayprovide important habitat for wintering and migratingraptors Because agricultural fields away from roads haveno perches of any kind we have worked with the farmmanager to install tall T-shaped perches in several interiorfields to provide access to more of the landscape bywintering raptors This may also assist in control of rodentsand other agricultural pests

DISTRIBUCION Y ABUNDANCIA RELATIVA DE AVESRAPACES DURANTE EL INVIERNO EN PAISAJESAGRICOLAS Y DE HUMEDALES EN EL SUR DEFLORIDA

RESUMENmdashInvestigamos la distribucion y abundanciarelativa de las aves rapaces entre ambientes agrıcolas ynaturales con base en censos realizados a lo largo de unaautopista de cuatro carriles en el sur de Florida durante losinviernos de 1998ndash2003 sin incluir el de 2001ndash02Registramos la presencia de acuerdo al tipo de coberturael uso de tipos de percha y la densidad de rapaces a lo

largo de la carretera ademas de la riqueza y diversidad deespecies en cada tipo de cobertura Cathartes aura Circuscyaneus Buteo jamaicensis y Falco sparverius fueron masabundantes en los paisajes agrıcolas que en los ambientesnaturales mientras que Coragyps atratus Pandion haliaetus yButeo lineatus fueron registrados con mayor frecuencia enlos ambientes naturales Encontramos un sesgo significa-tivo en el tipo de percha las lıneas electricas y los postesfueron empleados mas frecuentemente que las perchasnaturales Todas las especies fueron observadas con mayorfrecuencia de la esperada en uno o mas de los cinco tiposde percha o al vuelo Las siete especies se encontraron enambos habitats y la diversidad de especies fue general-mente igual entre estos Cada especie parecio exhibirdistintos patrones de uso de habitat y de perchas Nuestrosdatos sugieren que el paisaje agrıcola del sur de Florida esimportante para las poblaciones de rapaces invernantes ymigratorias

[Traduccion del equipo editorial]

ACKNOWLEDGMENTS

This research was supported by the Florida AgriculturalExperiment Station and a grant from the EvergladesAgricultural Area Environmental Protection District andapproved for publication as Journal Series No R-11011We would like to thank B Moser and J Bednarz forassistance with this manuscript

LITERATURE CITED

BOHALL PG AND MW COLLOPY 1984 Seasonal abun-dance habitat use and perch sites of four raptorspecies in north-central Florida J Field Ornithol55181ndash189

BUNN AG W KLEIN AND KL BILDSTEIN 1995 Time-of-dayeffects on the numbers and behavior of non-breedingraptors seen on roadside surveys in eastern Pennsylva-nia J Field Ornithol 66544ndash552

EAKLE WL EL SMITH SW HOFFMAN DW STAHLECKERAND RB DUNCAN 1996 Results of a raptor surveyin southwestern New Mexico J Raptor Res 30183ndash188

FULLER MR AND JA MOSHER 1981 Methods of detectingand counting raptors a review in CJ Ralph and JMScott [EDS] Estimating numbers of terrestrial birdsStud Avian Biol 6235ndash246

GARNER HD AND JC BEDNARZ 2000 Habitat use by Red-tailed Hawks wintering in the delta region of ArkansasJ Raptor Res 3426ndash32

GUNDERSON LH 1994 Vegetation of the EvergladesDeterminants of Community Composition in SMDavis and JC Ogden [EDS] Everglades the ecosystemand its restoration St Lucie Press Delray Beach FLUSA

IZUNO FT CA SANCHEZ FJ COALE AB BOTTCHER AND

DB JONES 1991 Phosphorus concentrations in drain-age water in the Everglades agricultural area J EnvironQual 20608ndash619

84 SHORT COMMUNICATIONS VOL 40 NO 1

LAYNE JN 1980 Trends in numbers of American Kestrelson roadside counts in southcentral Florida from 1968to 1976 Florida Field Nat 81ndash36

LEPTICH DJ 1994 Agricultural development and itsinfluence on raptors in southern Idaho Northwest Sci68167ndash171

LEYHE JE AND G RITCHISON 2004 Perch sites and huntingbehavior of Red-tailed Hawks (Buteo jamaicensis) J

Raptor Res 3819ndash25LIGHT SS AND JW DINEEN 1994 Water control in the

Everglades a historical perspective in SM Davis andJC Ogden [EDS] Everglades the ecosystem and itsrestoration St Lucie Press Delray Beach FL USA

MACARTHUR RH AND JW MACARTHUR 1961 On birdspecies diversity Ecology 42594ndash598

MACWHIRTER RB AND KL BILDSTEIN 1996 NorthernHarrier (Circus cyaneus) In A Poole and F Gill [EDS]The birds of North America No 210 The Academy ofNatural Sciences Philadelphia PA USA and TheAmerican Ornithologistsrsquo Union Washington DC USA

MEUNIER FD C VERHEYDEN AND P JOUVENTIN 2000 Use ofroadsides by diurnal raptors in agricultural landscapesBiol Conserv 92291ndash298

MILLSAP BA AND MN LEFRANC JR 1988 Road transectcounts for raptors how reliable are they J Raptor Res228ndash16

NEU CW CR BYERS AND JM PEEK 1974 A technique foranalysis of utilization-availability data J Wildl Manage38541ndash545

PEARLSTINE EV ML CASLER AND FJ MAZZOTTI 2005 Achecklist of birds of the Everglades agricultural areaFlorida Sci 6884ndash96

PEARLSTINE L S SMITH AND WM KITCHENS 2001 TheFlorida Gap Analysis Final Report USGS TechnicalReport 65 Published by National GAP ProgramMoscow ID USA

PORTER JW AND KG PORTER 2002 IntroductionThe Everglades Florida Bay and coral reefs of theFlorida Keys an ecosystem sourcebook in JW Porterand KG Porter [EDS] The Everglades Florida Bayand coral reefs of the Florida Keys an ecosystemsourcebook CRC Press Boca Raton FL USA

PRESTON CR 1990 Distribution of raptor foraging inrelation to prey biomass and habitat structure Condor92107ndash112

SIMPSON EH 1949 Measurement of diversity Nature163688

SMALLWOOD JA 1987 Sexual segregation by habitat inAmerican Kestrels wintering in southcentral Floridavegetative structure and responses to differential preyavailability Condor 89842ndash849

mdashmdashmdash 1988 A mechanism of sexual segregation byhabitat in American Kestrels (Falco sparverius) winteringin south-central Florida Auk 10536ndash46

SMALLWOOD SK BJ NAKAMOTO AND S GENG 1996Association analysis of raptors on a farming landscapePages 177ndash190 in DM Bird DE Varland and JJNegro [EDS] Raptors in human landscapes AcademicPress London UK

SORLEY CS AND DE ANDERSON 1994 Raptor abundance insouth-central Kenya in relation to land-use patternsAfr J Ecol 3230ndash38

THIOLLAY J-M AND Z RAHMAN 2002 The raptor commu-nity of central Sulawesi habitat selection and conser-vation status Biol Conserv 107111ndash122

WOFFINDEN ND AND JR MURPHY 1977 A roadside raptorcensus in the eastern Great Basin 1973ndash74 Raptor Res1162ndash66

ZAR JH 1984 Biostatistical Analysis Prentice Hall UpperSaddle River NJ USA

Received 12 January 2004 accepted 17 October 2005

MARCH 2006 SHORT COMMUNICATIONS 85

LAYNE JN 1980 Trends in numbers of American Kestrelson roadside counts in southcentral Florida from 1968to 1976 Florida Field Nat 81ndash36

LEPTICH DJ 1994 Agricultural development and itsinfluence on raptors in southern Idaho Northwest Sci68167ndash171

LEYHE JE AND G RITCHISON 2004 Perch sites and huntingbehavior of Red-tailed Hawks (Buteo jamaicensis) J

Raptor Res 3819ndash25LIGHT SS AND JW DINEEN 1994 Water control in the

Everglades a historical perspective in SM Davis andJC Ogden [EDS] Everglades the ecosystem and itsrestoration St Lucie Press Delray Beach FL USA

MACARTHUR RH AND JW MACARTHUR 1961 On birdspecies diversity Ecology 42594ndash598

MACWHIRTER RB AND KL BILDSTEIN 1996 NorthernHarrier (Circus cyaneus) In A Poole and F Gill [EDS]The birds of North America No 210 The Academy ofNatural Sciences Philadelphia PA USA and TheAmerican Ornithologistsrsquo Union Washington DC USA

MEUNIER FD C VERHEYDEN AND P JOUVENTIN 2000 Use ofroadsides by diurnal raptors in agricultural landscapesBiol Conserv 92291ndash298

MILLSAP BA AND MN LEFRANC JR 1988 Road transectcounts for raptors how reliable are they J Raptor Res228ndash16

NEU CW CR BYERS AND JM PEEK 1974 A technique foranalysis of utilization-availability data J Wildl Manage38541ndash545

PEARLSTINE EV ML CASLER AND FJ MAZZOTTI 2005 Achecklist of birds of the Everglades agricultural areaFlorida Sci 6884ndash96

PEARLSTINE L S SMITH AND WM KITCHENS 2001 TheFlorida Gap Analysis Final Report USGS TechnicalReport 65 Published by National GAP ProgramMoscow ID USA

PORTER JW AND KG PORTER 2002 IntroductionThe Everglades Florida Bay and coral reefs of theFlorida Keys an ecosystem sourcebook in JW Porterand KG Porter [EDS] The Everglades Florida Bayand coral reefs of the Florida Keys an ecosystemsourcebook CRC Press Boca Raton FL USA

PRESTON CR 1990 Distribution of raptor foraging inrelation to prey biomass and habitat structure Condor92107ndash112

SIMPSON EH 1949 Measurement of diversity Nature163688

SMALLWOOD JA 1987 Sexual segregation by habitat inAmerican Kestrels wintering in southcentral Floridavegetative structure and responses to differential preyavailability Condor 89842ndash849

mdashmdashmdash 1988 A mechanism of sexual segregation byhabitat in American Kestrels (Falco sparverius) winteringin south-central Florida Auk 10536ndash46

SMALLWOOD SK BJ NAKAMOTO AND S GENG 1996Association analysis of raptors on a farming landscapePages 177ndash190 in DM Bird DE Varland and JJNegro [EDS] Raptors in human landscapes AcademicPress London UK

SORLEY CS AND DE ANDERSON 1994 Raptor abundance insouth-central Kenya in relation to land-use patternsAfr J Ecol 3230ndash38

THIOLLAY J-M AND Z RAHMAN 2002 The raptor commu-nity of central Sulawesi habitat selection and conser-vation status Biol Conserv 107111ndash122

WOFFINDEN ND AND JR MURPHY 1977 A roadside raptorcensus in the eastern Great Basin 1973ndash74 Raptor Res1162ndash66

ZAR JH 1984 Biostatistical Analysis Prentice Hall UpperSaddle River NJ USA

Received 12 January 2004 accepted 17 October 2005

MARCH 2006 SHORT COMMUNICATIONS 85