j. Raptor Res. 25(4):140-141 ¸ 1991 The Raptor ResearchFoundation, Inc.

FOODHABITS Or THE GREATHOR•4ED OWL (Bubovirginianus) IN THE CAPE REGION OF LOWER CALIFORNIA•

JORGELLINAS-GUTIRRREZ, GUSTAVO ARNAUD AND MARCOS ACEVEDO Centrode InvestigacionesBioldgicas, Apdo. Postal 128, 2300 La Paz, B.C.S.,Mexico

On 4 May 1989 we discovereda adultsas the main feedingperch. Judging from the position (Bubo virginianus)nest with two young. The nest was where pellets and prey remains where found, adult owls locatedon the arms of a Cardon (Pachycereuspringlei) at consumedmainly large prey, but weightsranged between 4.3 m abovethe ground.Since little is known about Great 16.5 (pocketmice) and 1703 g (jackrabbits).On the con- trary, young owls apparently receivedmainly small and Horned Owls in , we studied the food medium-sizedprey, suchas Darkling Beetles(0.24 g) and habits of this pair. Wood Rats (125 g). Our results based on a single pair differ from those STUDY AREA AND METHODS reportedfor Great Horned Owls at other Mexican deserts The nestwas in an alluvialprairie (24ø08'N110•26'W) where the greatestproportion of the owls' diets included 17 km West of La Paz, Baja California Sur, Mexico, 635 rodents (42.7%), insects (19.0%) and arachnids (17.2%); m from the coastline and 6 m above sea level. Vegetation Donfizar et al. 1989). In our study lagomorphs(24.3%), consistedof fleshy stemmedshrubs about 2 m in height rodents (22.7%) and insects(16.5%) were the primary with Mesquite (Prosopisarticulata), Sweet Mangrove prey. Rodentsand lagomorphswere abundantin our study (Maytenusphylantoides), Torote and Copals(Bursera spp.), Adam's tree (Fouquieriadiguetii), Dagger Cactus (Ma- chaerocereusgummosus), Cholla Cactus( sp.), and Cardons as high as 7 m. We collected49 pelletsand prey remains from the ground below the nestCardon (Fig. 1) and elevenother locations in a 50 m radius on 16 and 24 May, and 3 and 9 June. Fledglingsleft the nestin the first week of June. Skeletal remainswere identified using the bird and col- lectionof Centro de InvestigacionesBio16gicas de Baja California Sur. Invertebrates were identified accordingto Chu (1949) and Borror et al. (1981). Identified prey were classifiedinto sevengroups, according to their phylogenetic affinities:lagomorphs, rodents, birds, CoastHorned Liz- ards, ophidia, insectsand centipedes,spiders and scorpi- ons.

RESULTS AND DISCUSSION (rodentsand lagomorphs)formed the bulk of prey consumed(Table 1). Jackrabbits(Lepus califor- nicus).Desert Cottontail (Sylvilagus auduboni), pocket mice (Peronathusspp.) and Darkling Beetles(Tenebrionidae) were the mostfrequently consumed prey species.Few rats (Neotornalepida and Dipodornysrnerriarni) and White- Footed mice (Perornyscuseva) were recorded. Crickets (Grillidae), Horned Beetles(Cerambicidae) and someun- identified coleopterans,comprised the secondmajor group (insectsand centipedes).Coast Horned Lizards (Phryno- somacoronaturn) and ophidia were the mostfrequent rep- tiles. Arthropods,such as arachnids(mainly scorpions), chilopodsand insects,including Darkling Beetles,were alsopresent. The least frequent prey were birds, spiders and scorpions.Rodents, insects and chilopodswere dom- inant at the nest Cardon; rodents and lagomorphswere dominantat the Cardon occupiedby adultsas main feeding perches. The greatestvariety of prey in owl pelletswas observed Figure 1. Vegetationshowing a Great HornedOwl nest at the nest Cardon, followed by a Cardon occupied by in a Cardonat E1 Comitfin,Baja CaliforniaSur, M•xico.

140 WINTER 1991 SHORT COMMUNICATIONS 141

Table 1. Prey (N = 115) recordedfrom 49 pelletsof the region (Arnaud and Acevedo 1990) and hence it is not Great Horned Owl, collectedin the locality E1 Comitfn, surprisingthat the proportionof lagomorphsin the diet Baja California Sur, May-June 1989. of the Great Horned Owls we studiedis three timeslarger than the 6.1% reportedby Donfizaret al. (1989) for the desertzone of Durango and Sonora, Mexico. NUMBER PER- PREY OF ITEMS CENT RESUMEN.--Seanalizaron 49 egagr6pilasarrojadas por una familia de TecolotesCornudos (Bubo virginianus) en Mammals un sitio de la region del Cabo, Baja California Sur, a Lagomorphs mediadosde 1989. Lostecolotes j6venes consumieron prin- Lepuscalifornicus 19 16.5 cipalmenteroedores, insectos ¾ cienpigs; los adultos comie- ron, sobretodo, lagomorfos¾ roedores. Esta dieta, basada Sylvilagusspp. 7 6.1 principalmenteen lagomorfos(24,3%) ¾roedores (22,7%), Unidentified 2 1.7 difiere muchode aquella reportadapara los tecolotescor- Rodents nudosde los desiertosde Durango ¾ Sonora, Mgxico, Perognathusspp. 13 11.3 dondelos lagomorfossolo 11egan al 6,1%, ¾en cambio los Peromyscuseva I 0.9 roedoresalcanzan el 42,7%. Esto puede indicar la gran selectividadde presas que estostecolotes pueden realizar Neotornalepida 4 3.5 localmente,favorecidos por la mayor diversidaden la flora Dipodornysrnerriarni 1 0.9 del firea, respectoa los otros desiertosmexicanos, donde Unidentified 7 6.1 su dieta es mils diversa. Total 54 47.0 ACKNOWLEDGMENTS Birds 6 5.2 We are grateful to Maria-Luisa Jimgnez and David Reptiles Auriolesfor criticallyreviewing the manuscript.We thank Lizards and toads also Armando Tejas for identifying the invertebrates. Phrynosornacoronaturn 6 5.2 LITERATURE CITED Sceloporussp. 1 0.9 ARNAUD,G. AND M. ACEVEDO. 1990. Hfibitos alimen- 8 7.0 ticiosde la zorra gris, Urocyoncinereoarœenteus (Car- Unidentified 3 2.6 nivora: Canidae) en la Regi6n Meridional de Baja Total 18 15.7 California, Mgxico.Revista de Biologœa Tropical 32(28): 499-502. Arachnids BORROR,D.J., D.M. DE LONGAND CH.A. TRIPLEHORN. Scorpions 8 7.0 1981. An introductionto the studyof insects.Saunders Spiders College Publishing Co., Philadelphia, PA. Lycosasp. 1 0.9 CHU, F.H. 1949. The immature insects. Wm. C. Brown Oliossp. 1 0.9 Co. Publishers.Dubuque, IA. Total 10 8.7 DON,•ZAR,J.A., F. HIRALDd,M. DELIBESAND R.R. ESTRELLA.1989. Comparativefood habits of the Ea- Centipedes gle Owl Bubo buboand the Great Horned Owl Bubo Scolopendromorpha 8 7.0 virginianusin six Paleattic and Nearcftc biomes.Ornzs Scandinavica 20:298-306. Insects

Coleoptera Received20 December 1989; accepted19 August 1990 Cerambycidae 3 2.6 Tenebrionidae 11 9.6 Unidentified 2 1.7 Hymenoptera Formicidae 1 0.9 Orthoptera Grillidae 2 1.7 Total 19 16.5