Range sizes and habitat use of non-breeding Crested Caracaras in Florida

J. Field Ornithol. 84(3):223–233, 2013 DOI: 10.1111/jofo.12022

Range sizes and habitat use of non-breeding CrestedCaracaras in Florida

James F. Dwyer,1,3,4 James D. Fraser,1 and Joan L. Morrison2

1Department of Fish and Wildlife Conservation, Virginia Tech, 100 Cheatham Hall, Blacksburg, Virginia 24061, USA2Department of Biology, Trinity College, 300 Summit Street, Hartford, Connecticut 06106, USA

3Current address: EDM International, Inc., 4001 Automation Way, Fort Collins, Colorado 80525, USA

Received 2 December 2011; accepted 25 April 2013

ABSTRACT. In Florida, habitats that include the breeding territories of Crested Caracaras (Caracara cheriway)are protected, but non-breeding individuals may be vulnerable because they may occupy different areas and habitats.We captured and radio-tagged 58 non-breeding caracaras in Florida from July 2006–March 2009, determined theirlocations during weekly flights, and used GIS and compositional analysis to evaluate range sizes and habitat use.Non-breeding caracaras (N = 58) ranged five times more widely during breeding seasons (N = 573 locations) thanduring non-breeding seasons (N = 592 locations), and ranged >250 times more widely than breeding caracaras thatdefend territories year-round. The large ranges of non-breeders suggest they may be searching for and evaluatingprospective territories or breeding opportunities (territory prospecting). Pasture occupied by cattle was the mostused habitat relative to availability and was used more than pasture without cattle, likely because insects associatedwith cattle are an important food source for caracaras. Cattle numbers in Florida are declining and, becauseboth breeding and non-breeding caracaras primarily occupy pasture, this may present difficulties for long-termmanagement. Citrus groves were also used more than expected given availability by non-breeding caracaras, but arerarely included in nesting territories. Because pasture and citrus were often adjacent, we suggest that citrus grovesmay function as refugia from socially dominant breeding caracaras. Conservation and recovery efforts for Florida’scaracara population are needed throughout the range of non-breeders, and should include management that ensuresavailability of habitat matrices of cattle pasture and citrus groves.

RESUMEN. Uso de habitat y extension de areas utilizadas por individuos no-reproductivosde Caracara cheriway en Florida

En Florida, el habitat que incluye el territorio reproductivo del Caracara crestado (Caracara cheriway) estaprotegido, pero los individuos no-reproductivos, pudieran ser vulnerables, debido a que estos ocupan habitats yareas variadas. De julio del 2006 a marzo del 2009, capturamos y le colocamos radiotransmisores a 58 individuos no-reproductivos de caracaras en Florida, y determinamos sus localizaciones durante sus vuelos semanales. UtilizamosGIS y analisis composicional para evaluar la amplitud de su distribucion y uso de habitat. Los individuos no-reproductivos (N = 58) se encontraron cinco veces mas ampliamente distribuidos durante la epoca de reproduccion(N = 573 localidades) que fuera esta (N = 592 localidades), y sus movimientos fueron mas amplios que loscaracaras reproductivos los cuales defienden el territorio a traves de todo el ano. El mayor uso de espacio porlos no-reproductores sugiere que estos muy bien pudieran estar buscando o evaluando territorios prospectivos y/ooportunidades para reproducirse. Los pastizales utilizados por ganado fue el habitat disponible mas utilizado y fueusado en mayor grado que los pastizales sin ganado, tal vez debido a que hay insectos asociados al ganado que sonfuentes importantes de alimento para los aves. La cantidad de ganado en Florida se esta reduciendo, y dado el casode que tanto las caracaras reproductivos como los no-reproductivo estan utilizando pastizales con ganado, esto muybien pudiera representar dificultades, a largo plazo, para el manejo de los caracaras. Aereas con cıtricos tambienfueron usados, en mayor grado que lo esperado, pero raras veces utilizado como territorio de anidamiento. Dadoel caso de que los pastizales y las areas con cıtricos con frecuencia estan adyacentes, sugerimos que las siembras decıtricos sirven de refugio de individuos reproductivos socialmente dominantes. Esfuerzos por conservar y recobrarla poblacion de caracaras de Florida son necesarios a todo lo largo de las areas utilizadas por los no-reproductivos, ydebe incluir manejo que asegure la disponibilidad de habitat de pastizales con ganado y sembrados de cıtricos.

Key words: Caracara cheriway, floater, Florida, raptor, seasonal range

Delayed maturation may evolve when theprobability of successful breeding is higher afterthe first year of life, when there is intense com-

4Corresponding author. Email: [email protected]

petition for resources, and when the penalty forlosing in resource competition is high (Hawkinset al. 2012). These criteria apply to many rap-tors, and raptor life cycles commonly includeone or more years between independence andestablishment of breeding territories (Newton

C© 2013 The Authors. Journal of Field Ornithology C© 2013 Association of Field Ornithologists

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224 J. F. Dwyer et al. J. Field Ornithol.

1998, Kenward et al. 2000). During this period,juveniles disperse from natal territories, imma-tures develop adult plumage, and adults searchfor breeding territories as floaters (Morrison andWood 2009, Penteriani and Delgado 2009, Blaset al. 2011). Such floaters would presumably en-ter the breeding population if breeding sites wereavailable (Newton and Rothery 2001, Penterianiet al. 2008).

Non-breeders are often secretive and foundin habitats not used by breeding birds(Newton 1992, Sergio et al. 2009, Schindleret al. 2012), perhaps because territory holdersexclude non-breeders from high-quality habitats(e.g., Schindler et al. 2012). If habitats used bynon-breeders and breeders differ, non-breedingindividuals may not be fully protected by conser-vation measures focused on maintaining habitatfor breeders (Dwyer 2010). Because survival ofnon-breeders can affect long-term populationpersistence (Rohner 1996, Penteriani et al. 2005,2011), data concerning the ranges and habitatsused by non-breeders should be incorporatedinto recovery and conservation planning (Ferrerand Harte 1997, Morrison and Wood 2009,Penteriani et al. 2011).

Crested Caracaras (Caracara cheriway; here-after caracaras) occur from northern SouthAmerica through the southwestern UnitedStates, with an apparently isolated population inFlorida (Morrison and Dwyer 2012). Breedingcaracaras have been well studied in Florida(Morrison and Humphrey 2001, Morrison andDwyer 2012, Dwyer et al. 2012b), less studied inTexas (Dickinson and Arnold 1996, Actkinsonet al. 2007) and Baja California (Rivera-Rodrıguez and Rodrıguez-Estrella 1998), andlittle studied elsewhere. Non-breeding caracarashave been studied only recently and only inFlorida (Morrison et al. 2008, Dwyer 2010,Dwyer et al. 2012a). Breeding caracaras are non-migratory, occupying nesting territories yearround. Most nesting (96%) is initiated fromOctober to March, with 61% of nesting initiatedfrom December to January (Morrison 1999).Young birds typically depart natal territories 4–6 mo after fledging (Morrison and Dwyer 2012).Non-breeding caracaras in juvenile, immature,and adult plumage are highly social and formmixed-age groups that regularly forage togetherand share communal roosts that can contain upto 300 individuals (Dwyer 2010). Age at firstbreeding can be as early as 3 yr and includes birds

in immature plumage (Nemeth and Morrison2002). However, some individuals persist inadult plumage without establishing breedingareas for at least 3 yr (Dwyer et al. 2012a), ap-parently because all breeding habitat is occupied.Non-breeding birds in adult plumage (floaters)have been described only in the Florida popula-tion, but it is not known whether this is becausefloaters do not occur in other populations orbecause other populations are less well studied.

The Florida population of Crested Caracarasis Federal and State listed as threatened and isbelieved to be declining due to habitat loss (US-FWS 1987, Logan 1997, Morrison and Dwyer2012). Conservation and recovery planning hasfocused on their breeding range and habitatbecause no quantitative data exist describinghabitat use by non-breeders. To be as effectiveas possible, conservation and recovery planningmust also include ranges and habitats occupiedby non-breeding caracaras (Nemeth and Mor-rison 2002, Dwyer 2010, Dwyer et al. 2012a).Thus, our objectives were to determine the areasand habitats used by non-breeding caracaras inFlorida.

METHODS

Our study area was a 43,000-km2 area thatincluded the entire known range of caracarasin Florida (35,000 km2; Morrison and Dwyer2012) and surrounding areas (Fig. 1). FromJuly 2006 to October 2008, we sought non-breeding caracaras throughout our study areaby driving public roads any place caracaraswere reported by contacts in the birding andregulatory communities. Much of the habitatoccupied by caracaras in Florida is privatelyowned (Morrison and Humphrey 2001) andbirds moved more rapidly between propertiesthan we could secure permission to access them.Thus, because caracaras regularly consume car-rion (Morrison et al. 2008), we used a trap baitedwith carrion to trap caracaras along the sides ofpublic roads wherever we found apparently non-breeding individuals.

Breeding status and age classes. We de-termined breeding status based on individualrange sizes. Morrison and Dwyer (2012) report∼90% of telemetry locations of breeding adultcaracaras (N = 28) occur within 2.5 km oftheir nest sites, and all locations occur within9 km. Therefore, we assumed that caracaras

Vol. 84, No. 3 Ranges and Habitat of Non-breeding Caracaras 225

Fig. 1. Locations (N = 1166) of non-breeding Crested Caracaras (N = 58) had a highly clustered distribution,resulting in a more limited and specifically defined range for the species in Florida, July 2006–March 2009. The1990s range estimate is based on USFWS 1999. Background map layers provided by the Florida GeographicData Library (www.fgdl.org).

that moved ≥10 km within a season were non-breeding.

We aged captured caracaras based onplumage, with juveniles having streaked breasts,immatures having breasts with a mix of streakingand barring, and adults having barred breasts(Morrison and Dwyer 2012). Caracaras tran-sition from juvenile to immature plumage atabout 12 mo, and attain adult plumage in 2to >4 yr (Voous 1983, USFWS 1999, Nemethand Morrison 2002). Because our study areawas mostly privately owned and individual birdsmoved widely, we rarely saw birds after we

marked them. Thus, we could not determinewhen individuals transitioned from juvenileto immature plumage and from immature toadult plumage. Consequently, we combined allnon-breeders for analyses. We determined thesex of each captured caracara by using DNAobtained from blood samples (Avian BiotechInternational, Tallahassee, FL). To collect blood,we inserted a needle into the ulnar vein andwithdrew 0.2–0.6 ml.

Telemetry. We used VHF-radio tagsto track non-breeding caracaras (AmericanWildlife Enterprises, Monticello, FL; Holohil,


Carp, ON, Canada; Advanced Telemetry Sys-tems, Isanti, MN; Wildlife Materials, Murphys-boro, IL). Tags weighed 30 g (<3% of theaverage body mass, mean body mass = 1125± 6.8 [SE] g, N = 183, Dwyer, unpubl. data),had mortality sensors, and were attached witha backpack harness (Buehler et al. 1995) madeof 64-mm Teflon ribbon (Bally Ribbon Mills,Bally, PA). When mortality sensors indicateda bird had died, we evaluated telemetry error(Withey et al. 2001) by comparing the habitattype assigned during aerial telemetry to thehabitat where the carcass was recovered.

We used an R-1000 receiver (Communica-tions Specialists, Orange, CA) to scan for signalsof marked birds during weekly 8-h telemetryflights in a Cessna 172 (Cessna, Wichita, KS),and found an average of 8.4 ± 0.7 (SE) birdsper week. When detected, signals were trackedto their source and we recorded locations usinga WAAS enabled GPSMAP 60Cx GPS receiver(Garmin International, Olathe, KS). To trackbirds, we continually turned the aircraft towarda detected radio signal until we were circlingan individual in a ∼0.5-km-diameter circle.Birds were assumed to be located at the centerof that circle when the telemetry signal wasequally strong along its entire circumference.To avoid bias by only searching areas wherewe expected to find caracaras, we generated 50random GPS coordinate locations within ourstudy area each week and developed a flight planto visit each of those locations. We typicallyreached 20–30 random locations, dependingon how often our flight plan was interruptedby detection of a signal. This protocol facili-tated searching our entire study area every 3–4weeks.

Ranges. We evaluated range sizes at fourscales, including: (1) collective year-round rangeof all tagged non-breeding caracaras, (2) collec-tive seasonal ranges of all tagged non-breedingbirds, (3) individual year-round ranges, and(4) individual seasonal ranges. Because 96% ofnesting attempts occur from October to March(Morrison 1999), we defined October–March asthe breeding season and April–September as thenon-breeding season. We used a multi-responsepermutation procedure (program BLOSSOM,Cade and Richards 2005) to determine if thedistribution of locations differed between breed-ing and non-breeding seasons both collectivelyand individually.

We used fixed kernels and reference smooth-ing (Seaman et al. 1999) in ArcGIS 9.2 (ESRI,Redlands, CA) to calculate 50% and 95% prob-ability contours as estimates of collective year-round and seasonal ranges. Collective rangesare variable because they accrue in part as afunction of the number of individuals sampled.To describe individual year-round ranges, welimited analyses to birds with ≥30 locations.To eliminate bias from unequal sampling, wecalculated probability contours using only thefirst 30 locations collected for each bird. Use ofthe first 30 points could cause bias if all pointswere collected early in a single season. However,because the 30 points accrued over the samemonths in multiple years, this bias was avoidedand this approach minimized the possibility thatthe last locations collected might have occurredin breeding territories that we failed to recognize.Few individuals yielded enough locations toconduct kernel analyses of individuals withinseasons so we used minimum convex polygons todescribe these areas. Minimum convex polygonsprovide information only about relative rangesin breeding and non-breeding seasons ratherthan true range estimates. To prevent bias, weused only the first 10 locations/bird/season todevelop minimum convex polygons.

Habitat. For habitat analyses, we includedonly birds with ≥10 locations. Each time wedetermined a bird’s location or reached a randomlocation, we recorded the land cover category.We compared land cover at random locations toland cover where birds were located to identifyhabitats used more than expected given theiravailability. On the basis of habitats importantto breeding caracaras and land cover types com-mon within the species’ range (Rivera-Rodrıguezand Rodrıguez-Estrella 1998, Morrison andHumphrey 2001, Morrison and Dwyer 2012),we categorized habitats as citrus groves, grass andsod (mowed grasses), pasture occupied by cattle,pasture not occupied by cattle, ≥10 sabal palm(Sabal palmetto) trees in a group that obscuredthe ground from the air, row crops includingsugarcane (Saccharum spp.), all forests, shrub,and scrub, except palm forests, open waterwithout emergent vegetation, urban areas (≥15anthropogenic structures within 100 m), andwetlands with emergent vegetation.

We evaluated habitat selection in the col-lective range of non-breeders and in individ-ual ranges (second- and third-order selection


sensu Johnson 1980) by comparing habitat typeswhere birds were located to habitat types atrandom locations. We defined random locationsavailable to non-breeding caracaras as any ran-dom location within 6 km of a telemetry loca-tion. We used 6 km because it was the longestdistance moved by non-breeding caracaras fromnocturnal roosts by 12:00 on the day followingroost use (Dwyer 2010). To assess the collectiverange on non-breeders, we compared the habitattypes at all telemetry locations to those at allrandom locations within 6 km of all teleme-try locations. To evaluate individual selection,we compared the habitat types at each bird’stelemetry locations to those at random locationswithin 6 km of that bird’s locations.

We used compositional analysis (Aebischeret al. 1993; Microsoft Excel tool ComposAnaly-sis version 5.1, Smith Ecology, Monmouthshire,Wales, UK) to evaluate habitat selection sowe could compare our findings with those ofMorrison and Humphrey (2001) who describedhabitat use by breeding caracaras. Using Com-posAnalysis, we determined the significance ofWilk’s � with 1000 iterations, and substituteda value of 0.01 for zero values in the matrixof land cover types (Aebischer et al. 1993,Manly 1997). Values are presented as means ±SE.

RESULTS

We radio-tagged 58 non-breeding caracaras in-cluding juveniles (N = 29), immatures (N =27), and adults (N = 2). We made 140 aerialtelemetry flights (mean = 7.8 h/week; 140consecutive weeks) from July 2006 to March2009. We tracked individual caracaras for 10–33 mo (mean = 17.0 ± 1.1 mo), and ob-tained 1166 locations of 58 individuals (Fig. 2).We obtained land cover information at alltelemetry locations and at 1040 random loca-tions. We collected ≥10 locations (mean = 24.5± 1.4 locations/bird, range = 10–42) for 44birds used to evaluate habitat selection. Samplessizes for birds used in range analyses differedfor collective versus individual and breedingseason versus non-breeding season analyses (SeeTable 1 for analysis-specific sample sizes). Allrecovered carcasses (N = 18 non-breeding,and one breeding caracara from a relatedstudy; Dwyer et al. 2012b) were in the land-

cover type and patch identified during aerialtelemetry.

Ranges. Ranges of non-breeding caracarasdiffered by season. On the basis of all locations ofall birds, non-breeding birds collectively movedmore widely during breeding seasons than non-breeding seasons (multi-response permutationProcedure, � = –3.4, P = 0.011; N = 573and 592 breeding and non-breeding seasonlocations, respectively; Table 1). The 50% coreuse area of all non-breeders combined increasedonly slightly following completion of the firstyear of the study, but the 95% use area increasedthroughout the duration of the study (Fig. 3).

Minimum convex polygons describing areasused by non-breeding caracaras were 4.9 timeslarger during the breeding season than the non-breeding season (t41 = –4.1, P < 0.001, N =17 breeding season, 26 non-breeding season).We found no difference between the rangesizes of males and females (95% home range,t16 = 1.3, P = 0.21; 95% use area: male =4841.2 ± 1256.1 km2, female = 3045.8 ±754.9 km2) regardless of season. Across seasons,ranges of individual birds varied in size from277 km2 to 11,285 km2 (mean = 3943 ±704 km2).

Habitat. Habitat use was disproportionalto availability for non-breeders collectively (� =0.03, � 2

9 = 148.1, P < 0.001) and individually(� = 0.11, � 2

9 = 97.4, P < 0.001). Thenumber of locations used was the same forboth analyses (N = 1076 telemetry locationsfrom 44 individuals, 1040 random locations),but assignment of random locations differedas described earlier. Pasture occupied by cattlewas the highest-ranked habitat collectively whendata from all 44 individuals was pooled, andindividually when each bird was included sepa-rately (sensu second- and third-order selection,respectively, Johnson 1980; Table 2). Citrusgroves and palm forests were the next highest-ranked habitats in collective and individual anal-yses followed by grasslands and pasture withoutcattle. Row crops, forests, shrubs, scrub, openwater, wetlands, and urban areas were not highlyranked in any analysis.

DISCUSSION

Range estimates. The collective range ofnon-breeding caracaras in our study was lo-cated almost entirely within the previous range


Fig. 2. Areas used by individual Crested Caracaras (N = the same 10 individuals illustrated for breedingand non-breeding seasons; N = 26 non-breeding and 17 breeding individuals in analyses) in Florida wereon average 4.9 times larger during the breeding season than the non-breeding season, July 2006–March2009. The 1990s range estimate is based on USFWS 1999. Background map layers provided by the FloridaGeographic Data Library (www.fgdl.org).

estimates for the species (based on USFWS 1999and indicated in Fig. 2 as 1990s range estimate),but did not include portions of that range thatmay not provide high-quality habitat. Collectiveranges are variable because they accrue in partas a function of the number of individualssampled. Although our information is limitedto a relatively small sample (N = 58 non-breeding caracaras), our 50% use area indicatesat least some of the areas important to largenumbers of individual non-breeders, and our95% use area may help identify the overall range

of caracaras in Florida. Additional high-use areasand a broader collective range would have beenlikely if more birds had been sampled, so theseranges represent guidelines for minimum areaswhere conservation and recovery actions shouldbe focused (50% areas) and at least considered(95% use area).

In kernel analyses, the 95% use area forall birds continued to increase long after the50% use area had stabilized. Non-breedingcaracaras regularly use communal roosts (Dwyer2010, Morrison and Dwyer 2012) where their


Table 1. Mean area estimates from range analyses for non-breeding Crested Caracaras in Florida, July 2006–March 2009.

Data type: individuals, seasons Kernel contours (km2) MCPa (SE) N birds N locations

50% (SE) 95% (SE)

Collective analyses, all seasons 4804 (–) 19,928 (–) – (–) 58 1166Collective analyses, breedingb 6125 (–) 23,757 (–)c – (–) 58 573Collective analyses, non-breedingd 4311 (–) 17,794 (–) – (–) 58 592Individual analyses, all seasons 820 (146) 3944 (705) – (–) 18 540Individual analyses, breeding – (–) – (–) 1181 (179) 17 170Individual analyses, non-breeding – (–) – (–) 241 (145) 26 260

aMCP = minimum convex polygon (km2).bBreeding season = October–March.cBreeding season range exceeds total range because total range is effectively an average of breeding season andnon-breeding season ranges.dNon-breeding season = April–September.

Fig. 3. The size of collective ranges of all non-breeding Crested Caracaras (N = 58) increased monthly inFlorida from July 2006 to March 2009.

movements appear to be centered during non-breeding seasons. We hypothesize that, in thefirst year of our study, we tracked caracaras toeach of the communal roosts in use by the speciesat the time and because non-breeding seasonmovements were centered on these locations, thecore use area stabilized relatively quickly. Non-breeding caracaras move more widely duringbreeding seasons so the 95% use area continuedto increase.

Ranges of individual non-breeding caracarasin our study (mean = 3943 km2) were >250times larger than reported previously for breed-ing caracaras (mean = 15.5 km2; Morrisonand Dwyer 2012) and were particularly largeduring the breeding season. We hypothesizethat non-breeding caracaras move in search ofor to evaluate prospective territories or breed-ing opportunities (territory prospecting) duringthe breeding season. Prospecting is expected


Table 2. Results from compositional analysis comparing proportional use of land cover types by 44 non-breeding Crested Caracaras (N = 1076 telemetry locations) to proportional availability of those land covers (N= 1040 random locations) in Florida, July 2006–March 2009. Ranks are shown according to randomizationtests with 1000 iterations.

Land Used habitatb Collectively available Individually available

Covera Proportion (95% CI) Rc Proportion (95% CI) Rc Proportion (95% CI)

OPAST 0.40 (0.34–0.45) 1 0.17 (0.13–0.20) 1 0.19 (0.17–0.22)CITRU 0.20 (0.14–0.27) 2 0.09 (0.06–0.12) 3 0.10 (0.07–0.13)UPAST 0.16 (0.13–0.19) 3 0.23 (0.19–0.28) 4 0.28 (0.24–0.31)GRASS 0.07 (0.05–0.11) 4 0.05 (0.03–0.07) 5 0.06 (0.05–0.08)PALMH 0.04 (0.02–0.05) 5 0.02 (0.01–0.04) 2 0.01 (0.01–0.02)ROWCP 0.06 (0.04–0.09) 6 0.08 (0.06–0.11) 6 0.08 (0.05–0.11)FORSS 0.04 (0.03–0.06) 7 0.21 (0.17–0.25) 8 0.16 (0.14–0.18)URBAN <0.01 (0.00–0.01) 8 0.03 (0.01–0.04) 9 0.02 (0.01–0.03)OPH2O <0.01 (0.00–0.00) 9 0.03 (0.01–0.04) 7 0.01 (0.00–0.02)WETLD 0.01 (0.01–0.03) 10 0.09 (0.06–0.12) 10 0.09 (0.07–0.10)

aOPAST = Occupied pasture (cattle present), CITRU = Citrus spp. in rows, UPAST = Unoccupied pasture(cattle absent), GRASS = Grass and sod, PALMH = Sabal palm (Sabal palmetto), ROWCP = Row cropsexcept citrus, FORSS = Forest, shrub, and scrub, URBAN = ≥15 structures within 100 m, OPH2O =Open water (no emergent vegetation), WETLD = Wetland (with emergent vegetation).bSelection was significant overall (Second-order selection: � 2

9 = 148.1, P < 0.001; Third-order selection:� 2

9 = 97.3, P < 0.001).cR = rank.

primarily during the breeding season whenindividuals can evaluate reproductive success(Boulinier et al. 1996, Balbontın and Ferrer2009). Prospecting is associated with increasedmortality of prospectors due to increased riskfrom intraspecific conflict and long-distancemovements through novel areas (Ferrer andHarte 1997). Consistent with the prospect-ing hypothesis, we found that ranges werelarger during the breeding season, and Dwyeret al. (2012a) reported survival of non-breedingcaracaras was significantly lower during breed-ing seasons than during non-breeding sea-sons. In a non-mutually exclusive hypothesis,non-breeding caracaras may also range morewidely during breeding seasons because breedingcaracaras are more aggressive in defending ter-ritories during this time. Finally, non-breedingcaracaras may move more widely during breed-ing seasons if the quality or availability of foodor foraging habitats differs seasonally, especiallyif breeding pairs occupy and defend the bestforaging habitat (Morrison et al. 2008).

Habitat. Pasture containing cattle was thehabitat most frequently used by non-breedingcaracaras in our study. Morrison and Humphrey(2001) also found that pasture was the highest-ranked habitat type for breeding caracaras in

Florida. Caracaras are strong runners that forageon foot in open habitats by scratching in soiland overturning debris in search of invertebrates(Morrison and Dwyer 2012). Pastures typicallysupport a variety of small vertebrate prey as wellas concentrations of invertebrates under cattlefeces, and invertebrates associated with cattleare an important part of the diet of caracaras(Morrison et al. 2008). The frequent useof pasture by non-breeding caracaras in ourstudy, along with similar findings for breedingcaracaras (Morrison and Humphrey 2001), sug-gest that availability of pasture is likely a primarydeterminant of the species’ range in Florida.Elsewhere in the species’ range, investigatorshave reported that caracaras are found in otherhabitats, including grassy hills (Donazar et al.1993), tallgrass prairie (Dickinson and Arnold1996), and savannah (Atkinson et al. 2007).

Little or no citrus grove habitat is typicallyfound in the territories of breeding caracaras inFlorida (Morrison and Humphrey 2001) and,in addition, few caracaras were observed incultivated lands on Caribbean islands (Nijmanet al. 2009). In contrast, non-breeding caracarasin our study used citrus groves more thanexpected given their availability. Because citrusgroves are often located adjacent to pastures


in Florida (J. F. Dwyer, pers. observ.) and be-cause field observations indicate that territorialadults can exclude non-breeding birds from theirbreeding areas (Morrison et al. 2008), we hy-pothesize that citrus groves may provide a refugethat non-breeding caracaras can occupy withoutattracting the attention or aggression of territo-rial breeding birds.

Nemeth and Morrison (2002) reported that∼5% of 160 individual caracaras marked asjuveniles were found breeding ≥3 yr post-fledgling we tracked 58 caracaras for 2–3 yr,including 27 individuals captured as immaturesand two as adults. These individuals were likelycapable of breeding, but did not exhibit rangesizes typical of breeding caracaras in Florida (≤9km from a central location; Morrison and Dwyer2012). The apparent long-term persistence ofcaracaras as floaters suggests that breeding habi-tat is both limited and saturated (Newton 1992,Hunt 1998), and we hypothesize that caracarasmay delay breeding and move widely in searchof breeding sites because habitat loss has re-stricted opportunities for recruitment. Alterna-tively, apparent floaters may have access to matesthrough extra-pair copulations (Dwyer et al.2012a).

Management implications. As a conse-quence of converting cattle pasture to other landuses such as urban development, cattle numbersin Florida declined nearly 30% from 2.4 millionin 1974 to a 1.7 million in 2007 (USDA 2007).Thus, availability of the most important habitat(pasture) for both non-breeding and breeding(Morrison and Humphrey 2001) caracaras inFlorida is declining. Because loss of breedinghabitat was a primary component of the reason-ing for listing caracaras as endangered in Florida(USFWS 1987, Logan 1997) and because themanagement plan for caracaras focuses on main-taining breeding habitat (USFWS 1999), ongo-ing declines in the most important habitat forthe species could potentially undermine recoveryefforts.

Management plans for threatened or endan-gered birds typically focus on breeding pop-ulations and management success is evaluatedin terms of productivity believed sufficient tomaintain the population (USFWS 1999, Perez-Garcıa et al. 2011). That focus is flawed if itdoes not ensure recruitment of non-breedingbirds into the breeding population (Ferrer andHarte 1997, Penteriani et al. 2005). The current

recovery plan for caracaras in Florida follows theparadigm of nest-centered protection (USFWS1999). Our results highlight the importanceof understanding habitat use by non-breedingcaracaras. We suggest that conservation andrecovery planning for Florida’s caracara pop-ulation should explicitly include non-breedingbirds and encourage a habitat matrix of pasturefor all life stages, citrus groves for non-breeders,and palm hammocks for breeders. Most of thehabitat occupied by caracaras occurs on privatelands (Morrison and Humphrey 2001). If man-agers and conservationists hope to successfullyprotect caracara populations, conservation ease-ments and public–private partnerships must beexpanded to provide private landowners withincentives to contribute to recovery goals.

ACKNOWLEDGMENTS

This study was funded by the U.S. Fish and WildlifeService grant no. 145 401815G060. This is contributionno. 145 from the MacArthur Agro-Ecology ResearchCenter (MAERC) of Archbold Biological Station. Wethank M. Ferrer, V. Nijman, G. Ritchison, S. Schubert,F. Sergio, and two anonymous reviewers for helpfulcomments on early drafts of this manuscript, R. Myersfor piloting telemetry flights, G. Lollis and P. Bohlen forlogistic support, and S. J. Chiavacci, J. L. Dowling, A. L.Fleming, M. R. Hanson, L. M. Hunt, A. K. Mangiameli,M. N. Scholer, N. E. Swick, and N. R. Thompson foraerial telemetry assistance. All animal handling protocolswere approved by the Virginia Tech Institutional AnimalCare and Use Committee (permit # 10–011-FIW).

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Documents

Range sizes and habitat use of non-breeding Crested Caracaras in Florida