j. RaptarRes. 31 (3) :228-233 ¸ 1997 The Raptor ResearchFoundation, Inc.

CRESTED C. kRACARA FOOD HABITS IN THE CAPE REGION OF BAJA CALIFORNIA, MEXICO

RICARDO RODI•GUEZ-ESTRELLA AND LAURA B. R_WERA RODI•GUEZ Centrode Investigaciones Biol6gicas del Noroeste, km 1 Cart. SanJuan de la Costa, E1 Comitdn, La Paz 23000 B. C.S., Mexico

ABSTR•CT.--Thediet of the CrestedCaracara (Caracara plancus) in the Cape region of Baja California, Mexicowas studied by analyzing195 pelletscollected beneath 10 occupiednests in 1990 and recording prey brought to two nestscontaining young in 1990-91. Our resultsshowed that Crested Caracarasfed opportunisticallyon mammals(mainly lagomorphs),reptiles (mainly iguanasand snakes),carrion of domesticanimals such as cattle and dogs,and invertebrates(mainly Coleoptera and Orthoptera). The caracaras'ability to kill live prey wasdenoted both by the high frequencyof reptile and bird remains in pellets, and by the high frequency of remains of recently killed birds, lizards and hares that were carried to nests. Our observations at nests indicated that Crested Caracaras killed as much as 63% of vertebrateprey in pellets,while invertebratesmay all havebeen capturedalive. Numerically, live prey comprisedabout 88% of the diet of caracarasin the Caperegion. In termsof ingestedbiomass, lago- morphs (both carrion and killed prey), reptiles (both carrion and killed iguanas,snakes) and carrion of cattle,represented the mostimportant food sources.We discussthe importanceof slaughterhouses, henhousesand garbagedumps for young caracarasin the Cape region. KEYWOgDS: Caracaraplancus; Crested Caracara; food; Baja California,Mexico.

H/tbitosalimenticios de Caracaraplancus en la regi6n del Cabo, Baja California, M•xico RESUMEN.--Ladieu del caracaracomfin (Caracaraplancus) fue estudiadaen la regi6n del Cabo, Baja California, Mfixico,analizando 195 egagr6pilascolecudas bajo 10 nidosactivos en 1990 y registrando las presastraidas a dosnidos conteniendo 3 y 1 pollosen 1990y 1991,respectivamente. E1 caracara es una rapaz oportunistaque se alimenta principalmentede lagomorfos,iguanas, culebras, carrofia de animalesdom6sticos, e invertebrados(cole6pteros y ort6pteros).De acuerdoa nuestrasobservaciones en nidos y al an/disisde egagr6pilas,estimamos que los caracarascazaron el 63% de los vertebrados, mientrasque losinvertebrados fueron todoscazados. Por lo unto, en t6rminosde frecuencia,las presas vivasrepresentaron alrededor de 88% de la dieta,aunque fueron lagomorfos y reptiles (presas y carrofia de ambosgrupos), y la carrofiade ganadoquienes proveyeron la mayorbiomasa. Se discutesobre la imporuncia de los mauderos, granjasav/colas y basurerosen la dieu de losj6venes caracarasen la regi6n del Cabo. [Traducci6n Autores]

Among caracaras, the Crested Caracara (Cara- Caracarais describedto be opportunisticbut large- caraplancus) is the specieswith the widest distri- ly carrion-feedingraptor (Sherrod 1978,Johnsgard bution in America, ranging from Florida, Texas 1990), although it may hunt living prey and steal and southern Arizona, through most of Mexico, food from other birds (Bent 1938, Hamilton 1981, particularlyin desertsand tropicalareas (Peterson Whitacre et al. 1982, Rodriguez-Estrellaand Rivera and Chalif 1973), south to Tierra del Fuego 1992). Descriptionsof its diet have been largely (Brown and Amadon 1968). In spite of its wide anecdotical and few quantitative data have been distribution,very little is known on the ecologyand published on variation in feeding habits through- feeding habitsof this species.Currently, studies on out its range (Bent 1938, Haverschmidt 1947, its breeding ecology are being carried out in dif- Sprunt 1954, Glazener 1964, Brown and Amadon ferent areas of its distribution (Texas, Dickinson 1968, Richmond 1976, Layne et al. 1977, Kilham and Arnold 1996; Mexico, Rodriguez-Estrellaet al. 1979, Thiollay 1980, Mader 1981, Whitacre et al. unpubl. data;Florida, J. Morrisonpers. comm.; Ar- 1982,Lyons 1988, Wallace and Temple 1987,Palm- gentina, A. Travaini pers. comm.). The Crested er 1988, Yosef and Yosef 1992, Dickinson 1995).

228 SEPTEMBER 1997 CRESTED CARACARA DIET IN MEXICO 229

Here, we presentinformation on the diet of a pop- were found feeding on roadkills, we recorded the speoes ulation of Crested Caracarasduring the breeding on which they were feeding. seasonin the Cape region of Baja California, Mex- RESULTS ico. CrestedCaracaras preyed on a broad variety of STUDY AREA vertebratesand invertebrates(B = 6.3). Prey spe- We studied caracarasin the xerophylous scrub vege- cies richnesswas over 60 species(Table 1). The tation of the Cape region of Baja California (109060'- mostimportant prey in termsof numberswere in- 111ø45'W, 25ø45'N). The vegetation is characterized by card6n (Pachycereuspringlei), dagger cactus (Stenocereus sects (mainly Orthoptera and Coleoptera) which gummosus),mesquite (Prosopis articulata), palo verde ( Cer- represented68% of the prey items identified (Ta- cidium microphyllum),Adam's tree (Fouquie•iadiguetii), ble 1, N = 2152). In terms of biomass, mammals plum tree (Cyrtocarpaedulis), copal (Burseraspp.), 1omboy (mainly Lepusand Sylvilagus)and reptiles (spiny- (]atrophacinerea) and cholla ( Opuntiacholla). The eleva- tailed iguana [Ctenosaurahemilopha], and snakes) tion of the area rangesfrom 0-250 m. This zone is char- acterized by a mean annual precipitation of 150.6 mm, a were the most important prey (almost80% of in- winter rainy seasonand an annual temperaturerange be- gestedbiomass, Table 1). We consideredthat small tween 22.1-23.4øC. mammals,birds, small to medium reptiles, and in-

METHODS sects,were preyed upon by caracarasas live prey because we recorded caracaras both carrying re- The breeding seasonof the Crested Caracara in the centlykilled items to the nest (Table 2) and killing Cape region extends from February-August. We collect- ed pellets and prey remains during the breeding season thoseprey. Whether mammalsand reptiles >500 g of 1990, particularly in April, May,June and July.Feeding appearing in pellets were captured alive and car- habitswere determined by analyzing195 fresh and whole ried to the nests remains unknown, but our obser- pellets collected in and around 10 occupied nests.As vationsof prey transportedto nestsby adultsmade Chi-squaretests did not detect significantdifferences in this seem doubtful. At nest 1, adults delivered one the type of prey appearingin pelletsfrom all nests(P > 0.05), we pooled all data. Pellets from nestslocated near mouse, five birds, one spiny-tailed iguana, one henhouseswere eliminated from the analysisto avoid an piece of a Iagomorph and one unidentified lizard. overrepresentationof carrion in the diet. For identifica- None of these were >500 g. At nest 2, one kan- tion, we compared remainsof skulls,bones, hairs, scales, garoo rat (Dipodomismerriami), two woodrats (Ne- feathers and invertebrateswith known reference speci- mens at the Centro de InvestigacionesBioltgicas del No- otomalepida), one bird, five lizards,one snakeand roeste (CIBNOR, Mexico). Prey remains in pellets were severalpieces of apparentlyfreshly-killed hares and identified to the closestpossible level of taxonomic res- rabbits,none of which were >500 g, were delivered olution. Food-niche breadth wasestimated using the Lev- (Table 2). We also observed adult caracaras hunt- •ns (B) index (Krebs 1989). Numbers of prey species were used for computationof niche breadth. ing, pursuingand killing hve prey on six occasions: As it wasnot possibleto determine whether mamma- two White-wingedDoves (Zenaidaasiatica), two Inca lian and reptilian prey representedin the pellets were Doves (Columbinapasserina) and two spiny-tailed captured alive or collected as carrion by caracaras,we iguanas.Again none of these prey were >500 g. made observationsfrom a blind at a nest one day (N• = Adult, but especiallyimmature caracaraswere 675 min) and at a secondnest for sevendays (N2 = 3102 min) to determine the proportion of prey types trans- frequently recorded feeding on carrion at hen- ported to the nestby adultsthat were freshly-killed(Rich- houses, slaughterhouses and garbages dumps mond 1976, Mader 1981). Nest 1, containingthree young (Rodriguez-Estrella1996). Most roadkills where near fledging age, wasobserved on 16 May 1991 and all caracaras fed were of hares (N = 20), cows (N = prey adults brought to the nest were recorded. In 1992, we made similar observations at nest 2 which contained 10), horses(N = 5), small reptiles (N = 5), small one young approximatelytwo wk old. We observedprey mammals (N = 5) and domestic dogs (N = 3). deliveries at this nest from 25 September-21 October, Caracarasalso fed on maggots (Cochliomyiamacel- when the young caracarafledged. We analyzedour data /at/a) at carcasses,adding up to 150 items that one in terms of ingestedbiomass. If a prey item was heavier adult ate in 5 min. Caracaras tended at times to than 500 g, we considered that the prey was probably consumed as carrion. Mean prey weightswere obtained follow tractors in fields being plowed catching from specimenstrapped in the field and from those grasshoppersand small mammalskilled by plow. stored at CIBNOR. Additionally, the number and age (immature, adult; DISCUSSION Clark and Wheeler 1987) of caracarasfeeding on carrion at slaughterhouses,henhouses and garbagesites were re- The Crested Caracara in the Cape region is an corded (Rodriguez-Estrella 1996). Whenever caracaras opportunisticraptor feedingon mammals(mainly 230 RODRIGUEZ-ESTRELLAAND RODRiGUEZ VOL. 31, NO. 3

Table 1. Diet of the Crested Caracara in the Cape region of Baja California, Mexico in 1990 as determined from 195 pelletscollected at nests.Totals show the numberof individualsper groupand the ingestedbiomass in grams. Asterisksindicate that computingweights were a maximum of 500 g.

SPECIES WEIGHT(g) % FREQ.1 % BIOM. % APPEAR.2

Mammalia Lepuscalifornicus 500* 3.6 21.9 39.5 Sylvilagusauduboni 500* 2.4 14.8 26.7 Ammospermophilusleucurus 102 0.8 1.0 9.2 Thomomysumbrinus 103 0.8 1.0 8.7 Chaetodipusarenarius 26.0 0.3 0.1 3.6 Dipodomysmerriami 42.0 0.3 0.1 3.1 Peromyscuseva 13.8 0.4 0.1 4.1 Peromyscussp. 13.0 0.05 tr* 0.5 Neotomalepida 148 0.3 0.5 3.1 Unidentified rodents 25.0 0.8 0.2 8.7 Canis latrans 500* 0.1 0.9 1.5 Spilogaleputorius 500* 0.05 0.3 0.5 Total s 213 71 959.1

Aves Falcosparverius 93 0.05 0.05 0.5 Callipeplacalifornica 189.5 0.1 0.2 1.0 Zenaida asiatica 152.9 0.8 1.6 9.2 Columbinapasserina 38 0.1 tr* 1.0 Geococcyxcalifornianus 210 0.2 0.5 2.1 Melanerpesuropygialis 54 0.4 0.2 4.1 Colaptesauratus 82 0.1 0.1 1.0 Myiarchuscinerascens 27.4 0.2 0.1 2.1 Aphelocomacoerulescens 84 0.4 0.4 4.1 Campylorhynchusbrunneicapillus 49 0.05 tr* 0.5 Phainopeplanitens 25.4 0.05 tr* 0.5 Cardinalis cardinalis 43 0.05 tr* 0.5 Icterus cucullatus 31.8 0.3 0.1 3.1 Polioptilacalifornica 6 0.05 tr* 0.5 Carpodacusmexicanus 21 0.3 0.1 3.6 Passer domesticus 22.4 0.05 tr* 0.5 Unidentified birds 25 3.0 0.9 32.2 Total 131 7606.4

Reptilia Callisaurus draconoides 23.9 0.1 tr* 1.5 Ctenosaurahemilopha 500* 1.9 11.9 21.5 Dipsosaurusdorsalis 60.7 0.6 0.4 6.7 Phrynosomacoronatum 36 1.9 0.8 20.5 Sceloporushunsakeri 52.5 0.1 0.1 1.5 Sceloporuslicki 16.5 0.9 0.2 10.8 Sceloporusmonserratensis 17 0.5 0.1 5.6 Sceloporuszosteromus 29.5 0.1 0.05 1.5 Cnemidophorusmaximus 24.9 1.2 0.4 13.3 Lampropeltisgetulus 229 0.1 0.4 1.5 Masticophisflagelum 300 0.6 2.2 6.7 Pituophismelanoleucus 280 0.2 0.8 2.5 Salvadorahexalepis 170 0.2 0.4 2.1 Crotalusenyo 500* 0.2 1.1 1.5 Crotalus ruber 500* 0.4 2.3 4.1 Unidentified reptiles 25 0.2 0.1 2.6 SEPTEMBER 1997 CRESTED CARACARA DIET IN MEXICO 231

Table 1. Continued.

SPECIES WEIGHT(g) % FREQ.1 % BIOM. % APPEAR.2 Unidentified snakes 500* 2.7 16.8 28.7 Total 263 67 038.1 Invertebrata Arachnida 0.5 0.05 tr* 0.5 Theraphosidae 5.0 0.05 tr* 0.5 Scorpionidac 2.0 0.6 tr* 6.2 Solifugae 0.5 0.2 tr* 0.5 Chilopoda 2.0 0.1 tr* 0.5 Coleoptera 0.5 0.7 tr* 7.2 Carabidae 0.37 0.7 tr* 5.1 Scarabaeidae 0.5 0.5 tr* 3.1 Tenebrionidae #1 0.5 10.9 0.06 40.0 Tenebrionidae #2 0.13 4.3 tr* 20.5 Cerambycidae 1.0 0.3 tr* 2.1 Orthoptera 0.75 0.2 tr* 1.5 Gryllidae 1.0 29.9 0.4 37.9 Acrididac 2.0 11.8 0.3 26.7 Tettigonidae 1.0 0.2 tr* 1.5 Dermaptera Formiculidae 0.5 3.1 tr* 9.2 Hymenoptera 0.5 0.4 tr* 2.6 ¸donata 1.0 0.05 tr* 0.5 Diptera 0.5 0.05 tr* 0.5 Unidentified 1.0 4.1 0.05 22.6 Total 1466 1470.4 Unidentified carrion 500* 3.7 15.6 40.5 Total 79 27 300.0 GRAND TOTAL 2152 175 374.0 * tr < 0.05% of total prey biomass. • Total number of individualsof each prey type X tOOdivided by the grand total number of prey. 2 Number of occurrencesof each prey type X tee dividedby the total number of pellets;because of this, the sum of frequencies may be above tee. • Total number and biomassper group lagomorphs),reptiles (mainly iguanasand snakes), according to our direct observations,we estimated carrion of domesticanimals such as cattle and dogs, that caracaraskilled about 63% of vertebrateprey and invertebrates(mainly Coleoptera and Orthop- in pellets (consideringconservatively that 35% of tera). Its opportunismis evidencednot only by the lagomorphs were captured as live prey). We as- breadth of its food niche, but also by the fact that sumed that all invertebrateswere all captured as as many as nine prey speciescan be found in a live prey. Based on our numerical analysisof the single pellet. The caracara'sability to kill live prey diet, we felt that live prey represented88% of the is denoted by the high frequency of mobile prey diet of caracarasin the Cape region. However, in including reptiles and birds that appear in pellets terms of ingested biomass,lagomorphs (both car- and are brought to nests,apparently having been rion and killed prey), reptiles (both carrion and captured alive. Its predatory ability is also demon- killed spiny-tailediguana and snakes)and carrion stratedby the six captureswe observedof live prey of cattle, represented the most important food (dovesand lizards) and observationsof activeprey sources. In Texas, Dickinson (1990) found that the pursuit and capture elsewhere(Richmond, 1976, majority of the caracara'sdiet at nest sitesconsisted Layne et al. 1977, Whitacre et al. 1982). of live-caughtprey (61%), with carrioncomprising We were not certain as the proportion of lago- 39%. morphs that were taken as carrion or live prey but, Crested Caracaras in Baja California fed nest- 232 RODR•GUEZ-ESTRELLAAND RODRIGUEZ VOL. 31, No. 3

Table 2. Prey items brought to nestsof the CrestedCaracara in the Cape region, Baja California, Mexico.

PREY NUMBER NOTES

Nest 1, 16 May 1991 Mammals Lepuscalifornicus 1 1 piece of leg Unidentified rodent 1 complete item Birds Zenaida asiatica 1 complete item Carpodacusmexicanus 1 complete item Unidentified bird 3 20-30 g, complete Reptiles Ctenosaurahemilopha I complete item Unidentified lizard I complete item Total items 9 Rate/day 9 Rate/hour 0.80 Nest 2, 25 September-21 October 1992 Mammals Sylvilagusaudubonii 2 1 leg, 1 head Lepuscalifornicus 12 8 piecesof legs, 2 heads Dipodomysmerriami 1 complete item Neotomalepida 2 complete item Birds Unidentified bird 1 20-30 g, complete Reptiles Cnemidophorussp. 3 complete item Sceloporussp. 2 complete item Unidentified snake 1 ca. 100 g fresh snake Total items 24 Rate/day 5 Rate/hour 0.46 lings mainly with vertebrateprey capturedalive, as numbers of invertebrates (mainly Orthoptera). observed in studies elsewhere (Richmond 1976, Thus, these feeding areas are probably important Mader 1981), but proportions of prey groups dif- for young caracarasin the Cape region. Indeed, fered. Levy (1988), analyzing30 pellets collected what appeared to be family groups of two adults beneath a negt in Arizona, found that 26% of the and one to three young were commonly observed pelletscontained scales of Phrynosomalizards, 93% during the postfledgingperiod feeding on human contained arthropod remains, and seldom were refuse sourcesand agriculturalareas (35.1%, N = hairs of lagomorphs identified. Dickinson (1990) 74 group observations).We had the impression reported that invertebrate prey brought to the that adults lead juveniles to predictable food nestsaccounted for only 3% of items. sources.Additional studieson feeding behavior of Immature caracarasseem to depend mainly on immature and adult caracaras during the post- carrion and invertebrates during the postfledging fledging period deservefurther attention in order period as evidencedin our observationsthat most to better understandthe processby whichjuveniles immatures foraged near slaughterhouses, hen- learn to find predictable food sources. houses, garbage sites (Rodriguez-Estrella 1996) and cultivated areas rather than in natural areas. ACKNOWLEDGMENTS Carrion in human refuse areas is a predictable Specialthanks are given to A. Tejas for advicein the source of food and cultivated areas attract high identification of arthropods. F. Anguiano and E. Mata SE•'TEMBER1997 CmOSTEDC•m•C• DIET IN MEXICO 233 helped in observationsof nests.D. Whitacre and E Jaksi• LEVY, S.H. 1988. Status and distribution of the Crested made valuablecomments that improved the manuscript. CaracaraPolyborus plancus audubonii Cassin 1865 in Ar- Centro de InvestigacionesBioltgicas del Noroeste and izona. Tech. Rep. Arizona Game and Fish Depart- CONACyT (1749P-N) provided financial support. LRR ment, Phoenix, AZ U.S.A. received a grant from CONACyT. RRE received a grant LYONS,J. 1988. The uncommon caracara. TexasParks and from CSIC-Spain that helped support completion of this work. Wildlife46:8-11. M•,I)ER,W.J. 1981. Notes on nesting raptors in The Lla- LITERATURE CITED nos of Venezuela. Condor 83:48-51. PALMER, R.S. 1988. Handbook of North American birds, BENT, A.C. 1938. Life histories of North American birds Vol. 5. Yale Univ. Press, New Haven, CT U.S.A. of prey, Part 2. U.S. Natl. Mus. Bull. # 170. PETERSON,R.T. ANDE.D. CHALI1r. 1973. 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