J. Field Ornithol., 65(2):258-264

THE FOOD HABITS OF SYMPATRIC CICCABA IN NORTHERN GUATEMALA

RICHARD P. GERHARDT 1 Raptor ResearchCenter BoiseState University Boise, Idaho 83725 USA

DAWN MCANNIS GERHARDTAND CRAIGJ. FLATTEN The PeregrineFund, Inc. 5666 West Flying Hawk Lane Boise, Idaho 83709 USA

NORMANDY BONILLA GONZALEZ El ParqueNacional Tikal El Peten, Guatemala

Abstract.--The food habits of eight breedingpairs of Mottled Owls (Ciccabavirgata) and a singlenesting pair of Black-and-whiteOwls (C. nigrolineata)were studiedin Tikal National Park, Guatemala. Both speciescaptured large insects,including beetles(primarily scara- baeid,curculionid and cerambycid),grasshoppers (Orthoptera; Acrididae), and cockroaches (Orthoptera; Blattidae). There was little overlap in the vertebratecomponent of the diets of the two species;Black-and-white Owls fed on (especiallyArtibeus jamaicensis), whereasMottled Owls ate small rodents(including Oryzomysfulvescens and Sigmodonhis- pidus). One hundred percentof Black-and-whiteOwl pelletscontained insect exoskeletal material; 73% containedbat fur and/or bones.Ninety-eight percentof Mottled pellets contained insect matter, whereas 56•o contained vertebrate remains.

LOS H•i, BITOS ALIMENTICIOS DE LECHUZAS DEL GP•NERO CICCABA EN EL NORTE DE GUATEMALA Sinopsis.--Loshfibitos alimenticios de ochoparejas de Ciccabavirgata y de una pareja de C. nigrolineatase estudiaronen el Parque Nacional de Tikal, Guatemala. Ambasespecies capturaroninsectos grandes, tales comoescarabajos (principalmente escarabeidos, curculi6- nidosy cerambicidos),saltamontes (Orthoptera: Acrididae), y cucarachas(Orthoptera: Blat- tidae). Se hall6 poco solapamientoen el componentevertebrado de la dieta de estasdos especies:C. nigrolineatase aliment6 de murci•lagosmientras que C. virgatase aliment6de roedotespequefios (inclvyendo Oryzomys fulvescens y Sigmodonhispidus). Todos los egagr6- pilos de C. mgrolineatacontenlan material exoesqueletalde insectos;73% conteniapelaje y/o huesosde murciglagos.Noventa y ocho por ciento de los egagr6pilosde C. virgata contenianmaterial de insectosy 56% contenlarestos de vertebrados. The foot habits of owls of the Ciccabaare not well known. Detailed accountsof prey and feedingbehavior have been reportedfor only Ciccabawoodfordii, the sole Old World representativeof this genus (Harvey 1977, Steynand Scott1973). New World Ciccabainhabit Neo- tropical forestswhere they are mostly unstudied(Burton 1973), and knowledgeof their food habits has comefrom isolatedobservations and from stomachcontent analysis of a few collectedspecimens (Buchanan 1971, Burton 1973, Marshall 1943, Wetmore 1968).

Currentaddress.' The PeregrineFund, Inc., 5666 WestFlying Hawk Lane, Boise,Idaho 83709.

258 Vol.65, No. 2 Foodof Ciccaba Owh [259

The Black-and-whiteOwl (C. nigrolineata)inhabits humid lowland and foothill forests from southern Mexico to northwestern Venezuela and northwesternPeru. The literature for this speciesis limited mostly to brief anecdotaldescriptions and accountsof individuals(Grossman and Hamlet 1964, Land 1963, Smithe 1966). The Mottled Owl (C. virgata)is believedto be the mostnumerous and widespreadwood owl of the neotropicsand subtropics.Its range extends from Chihuahuaand Sonora,Mexico to northernArgentina and southern Brazil (Petersonand Chalif 1973), and it has been reportedas far north as Hidalgo County, Texas (Lasley et al. 1988). The Black-and-whiteOwl is the larger species,with bodymass reported as 440-500 g (Burton 1973), whereasthe male and female capturedin this studyhad bodymasses of 435 and 536 g, respectively.Mottled Owls have been reportedto weigh between 176-305 g (Burton 1973, Voous 1988). In this study, sevenadult males had a mean body mass of 239.7 + 13.3 (SD) g (range = 220-256 g), and nine adult femaleshad a mean bodymass of 335.6 + 13.7 g (range = 308-366 g). The Black-and-white Owl is considereduncommon to rare throughoutits range (Petersonand Chalif 1973, Stiles and Skutch 1989), and our observationsshow this is true in northern Guatemala as well. The Mottled Owl is quite abundant in this same area (Gerhardt 1991a,b). As part of a comprehensivestudy of Neotropicalraptors in Tikal National Park, Guatemala (Burnham et al. 1988), we studied the food habits of a single nestingpair of Black-and-white Owls during three consecutivebreeding seasons,1989-1991. During 1990-1991, we si- multaneouslystudied the feedinghabits of eight pairs of breedingMottled Owls.

STUDY AREA The 576 km2 Tikal National Park is locatedin the Department of Peten in northeasternGuatemala (17ø13'N, 89ø38'W). Physiographyof this region is low rolling hills of eroded limestonesranging to 250 m abovesea level. Surfacewater is limited to rain-filled pondsand extensive woodedswamps called bajos, which are floodedduring the wet season (July-January). The tropicalclimate is consideredrelatively dry with an averageannual precipitationof about 1400 mm. Mean temperatures rangefrom 10 C on coolnights to 28-35 C duringthe day (Smithe1966). Vegetationis semideciduoustropical dry forest (Holdridge 1957), and grows in dense, continuousstands in undisturbed areas. Predominant foresttypes include climax, woodedswamp, and transitionzone (Lundell 1937). Topography and the degreeof inundation during the wet season largely determine the distribution of forest types. The more common climax forest grows on better-drained,higher areas where tall trees (to 50 m) generallyform a continuous,multi-tiered overstoryand relatively thin to moderateunderstory. Major tree associationsare characterizedby zapote(Manilkara archas),ramon (Brosimumalicastrum), and caoba(ma- hogany,Swietenia macrophylla). Wooded swamp grows on poorly-drained, 260] R. P. Gerhardtel al. J.Field Ornithol. Spring 1994 fiat bajoswhere treesare generallyless than 15 m tall, overstoryis mostly non-existent,and understoryis a dense growth of small trees, thorny shrubsand vines.Palo tinta (Haemotoxylumcampechianum) characterizes the major tree association.Transition zone forest grows on moderately- drained groundbetween climax forestand woodedbajo, where tree height, overstoryand understory density are intermediate between these forest types. Escobapalm (Chrysophilaargentea) and botan palm (Sabal sp.) characterize transition zone forest.

METHODS As part of a breeding biology and home range study, we located 13 Mottled Owl and four Black-and-white Owl nests,and followed a single Black-and-white Owl male and seven Mottled Owl males with radio- telemetry.Data on food habitswere gatheredby observingprey deliveries or exchangesduring nestobservations or radio-tracking,and by analyzing pelletsthat were collecteddaily under diurnal roosts.Also, we collected a small number of fresh prey remains after climbing to nests.Although radio-trackinggreatly facilitated the locationof diurnal roosts,we were frequently able to find the roostsof other Mottled Owls that were not radio-tagged. Quantificationof prey was basedon pellet analysis,because prey re- mains and direct observationsyielded so few data. As it was not possible to count the number of prey individuals in pellets, we determined fre- quencyof occurrenceby dividing the number of pellets in which each prey taxon was found by the total number of pellets (Marti 1987). Analysisof the dietsof both specieswas madedifficult by severalfactors. Nestswere kept quite clean,and we rarely found prey remains.Moreover, pelletswere discardedat somedistance from nests,and adultsapparently carried off pellets regurgitatedby the young, as none were found in or below nests.More importantly, pelletsdisintegrated quickly in the tropical forest, and little remained after a single day. As only chitinous remains of insectsare found in pellets(Marti 1987), soft-bodiedinsects would be detectedonly through direct observation.

RESULTS Mottled Owls.--We found the following items in Mottled Owl pellets: coleopterans(Scarabaeidae, Curculionidae, and Cerambycidae),orthop- terans (families Acrididae and Blattidae), anole lizards, the rice rat, Ory- zomysfulvescens, the cottonrat, Sigmodonhispidus, and a small, uniden- tified . Of the 52 pellets(or partsthereof) that we collected,23 (44%) contained only insectparts, and only one (2%) failed to contain at least someinsect exoskeletalmaterial. Insectsfound most commonlyin pelletswere scar- abaeidbeetles and acridid grasshoppers,with cockroachesand both cur- culionid and cerambycidbeetles found lessfrequently. These were gen- erally representedby intact legs;beetle elytra were typicallybroken into small bits. Twenty-six (50%) of the pelletscontained bones and/or fur Vol.65, No. 2 Poodof Ciccaba Owls [261 of rodents.The majority of these belongedto rice rats and cotton rats. Lizard mandibleswere found in two pellets, and the jaw of a small bat was found in one pellet. Thus, while insectswere found in nearly all pellets,vertebrates were representedin 56% of pellets. We found nine items as prey remains in Mottled Owl nests.These includeda large snoutbeetle (Coleoptera; Curculionidae), two cockroach- es (Orthoptera;Blattidae), a treefrog(Hyla sp.), a ranid frog, a lizard (Anolissp.), a big-earedclimbing rat (Ototylomysphyllotis), a rice rat (Oryzomysfulvescens),and the feathersof a small, unidentifiedbird. We observedMottled Owls catchingor carryinga katydid(Orthoptera; Tet- tigoniidae) and two rice rats. Mottled Owls typically hunted in denseclimax forestand exclusively at night. Low percheswere commonlyused, and most of the rodents capturedwere terrestrial species.One male, whosehome range included human habitations,spent time hunting rats near kitchen facilities. Black-and-whiteOzals.--We collectedmaterial from 73 pellets from under the roostsof the radio-taggedmale and his mate. All pellets con- tained someinsect exoskeletal material, and 19 (26%) consistedonly of insectmatter. Fifty-three (73%) of the pelletscontained fur and/or bones of chiropterans.Only when someportion of the skull was includedwere we able to identify the speciesof bat eaten. Of 21 skulls identified, 13 were fruit bats,Artibeusj'amaicensis, five were black mastiff bats,Molossus ater, two were wrinkle-faced bats, Centurio senex, and one was a tent- makingbat, Urodermabilobatum. We found rodentprey in but two pellets; one pellet containedthe mandibles of a small rat, probably Oryzomys fulvescens,and the other containeda singlerodent incisor. Although feath- ers were found in nine pellets, in four of thesethey were from the owl itself. Thus, five pellets(7%) containedfeathers of unidentifiedbird prey. Also presentin 10 (14%) of the pelletswere seedsof Psidiurnsp., which we believe to be from bat stomachs. All of the insectsidentified in Black-and-white Owl pellets were co- leopteransor orthopterans.Scarabaeid beetles were the most commonly identifiedinsects, and were representedby legs,elytra, pronotaand head capsules.Subfamilies of scarabsincluded Scarabaeinae(dung beetles), Geotrupinae (earth-boringdung beetles),Melolonthinae (June beetles), and Dynastinae (unicorn beetles). Snout beetles (Curculionidae) were identifiedfrom elytra and from headcapsules. Long-horned beetles (Cer- ambycidae),less commonly found, were representedby fragmentsof elytra and by their heads,whereas hydrophilid beetles were identifiedby the sharp spineof the metasternum.Short-horned grasshoppers (Orthoptera; Acrididae) were found infrequently,with the femur and tibia remaining intact, and cockroaches(Orthoptera; Blattidae) were representedby frag- mentsof their pronota. Black-and-whiteOwls hunted exclusivelyat night. We observedthe radio-taggedmale hunting on numerousoccasions, particularly in the semi-open area near one of three ponds within his home range. He generallyperched 2-5 m in height on a branch or post near the water's 262] R. P. Gerhardte! a/. J.Field Ornithol. Spring 1994 edge.From this perch,the owl flew short distancesafter beetlesand bats. On one occasion,he was observedflying after a bat through the forest; this chase was somewhat longer than other observedprey capture at- tempts, and the bat eluded his pursuer. Black-and-white Owl nests were checked much less often than those of Mottled Owls, and the only prey remain found was from a fruit bat, A. jamaicensis.

DISCUSSION Femalesof both speciesperformed all of the incubatingand brooding. Thus, for most of the period of this study, males did all of the hunting. When not incubatingor brooding,however, females often roostedwith their mates, and we could not attribute pellets to one or the other with any certainty.Nonetheless, the majority of pelletsfound in this study,for both species,were cast by males. It is noteworthythat Mottled Owls were found to be highly dimorphic (Gerhardt 1991b) and that the pair of Black-and-white Owls was only slightly less dimorphic. Thus, males and femalesof each speciesmight be expectedto capture different sizesor taxa of prey. Our resultsshould thereforebe interpretedwith the caveatethat they largely representthe food habits of males. Furthermore, we found severalmajor taxa at nests that were unrepresentedin pellets. This may be due to their not being preservedin pellets. Another possibility,however, is that certain prey types are fed preferentially to nestlingsand that pellets found at the diurnal roostsof malesmay not accuratelycharacterize the diet of a family of owls. Althoughquantitative analysis of their diet is thereforesomewhat prob- lematical, it seemsclear that Mottled Owls are primarily insectivorous. Vertebrate remains are likely to be better preservedin pellets than are arthropod parts, and any bias in pellet analysisshould be towards over- estimatingthe proportionof vertebratesin the diet. Despitethis bias,44% of all pelletscollected contained only insectparts, and all but one pellet containedat leastsome insect material. Clearly, insectsare the principal component,by numbers,of the diet of Mottled Owls in our study area. The isolatedobservations and stomachcontent analysesof other re- searchersalso identify insectsand small rodents as principal prey of Mottled Owls (Buchanan 1971, Burton 1973, Wetmore 1968). Burton (1973) reported reptiles as prey of this species,and Wetmore (1968) recordeda small snake among observedprey items in Panama. Lizards are not specificallyreported, nor are frogs. Wetmore (1968), however, recordeda salamanderas Mottled Owl prey, and Burton (1973) reported that the diet includes small . Buchanan (1971) identified the het- eromyid rodent Hereforaysanomalus as a prey speciesin Trinidad. Black-and-white Owl pellets containedmostly coleopteransand chi- ropterans.Pellets, however,do not necessarilyreflect the entire breadth of the diet, nor are the prey found in pelletslikely to be representedin Vol.65, No. 2 ];•odof Ciccaba Owl• [263 direct proportionto the relative frequencyof their being ingested.Spe- cifically,bones, fur and beetleelytra are more likely to appear in pellets (lesslikely to be digested)than are the bodyparts of soft-bodiedinsects. Indeed, Burton (1973) mentionstettigoniids and cicadidsas prey items of Black-and-whiteOwls althoughwe did not identifyeither of thesesoft- bodied insectsin the pellets we collected.Nonetheless, it is clear that insectsand bats are typical prey of theseowls. Again, our resultsare in agreementwith the few previouslypublished reports.In E1 Salvador,Marshall (1943) collecteda male whosestomach containedgrasshoppers and two bats, and he collecteda female that had been hunting grasshoppers.Burton (1973) describedthe diet of Black- and-white Owls as includingbats and large insects(beetles, tettigoniids and cicadas).In Venezuela, Ibafiez et al. (1992) collectedpellets from beneaththe roostsof a pair of theseowls during a 5-wk period. These pelletscontained the samegeneral taxa of prey, but bats and birds rep- resenteda much larger proportionof the prey numbers.This latter finding may be an artifact of the short duration of the samplingseason, rather than a real differencebetween owls in the two study areas. There is both overlap and divergencein the prey of the sympatric speciesof Ciccabain Tikal. Ninety-eight percentof Mottled Owl pellets and 100% of Black-and-whiteOwl pelletscontained insect remains. Both speciesfed on scarabs,short-horned grasshoppers, snout beetles,long- horned beetlesand cockroaches.Black-and-white Owls also took hydro- philid beetles,whereas Mottled Owls ate katydids.Only 56% of Mottled Owl pellets containedvertebrate remains, whereasvertebrate parts were foundin 73% of Black-and-whiteOwl pellets.There was, moreover,little overlapin this vertebratecomponent of the diets. Only one Mottled Owl pellet containedbat remains; lizard mandibleswere representedin two pellets, and rodent parts were found in 50% of the pellets. In contrast, all of the vertebrateremains in Black-and-white Owl pellets were chi- ropteran, except for a pair of small rodent mandibles,a single rodent incisor, and a few small feathers.

ACKNOWLEDGMENTS

This researchwas conductedas part of the Maya Projectof the PeregrineFund, Inc., and we thank the people,trusts and foundationsthat supportthis organization.Funding was also provided to RPG by Boise State University and by the Frank M. Chapman Memorial Fund and the American Museum of Natural History. Assistingin data collection were Israel Segura,Apolinario de JesusMendoza, Crist6bal Mateo Morales, Edi Rubl Martinez L6pez and Miguel Angel VfisquezMarroquln. We would alsolike to thank St. RogelChi Ochaetaof Tikal National Park for his supportand cooperation.Jim Thomason of the Florida Museum of Natural History (University of Florida) aided in identifyingthe Ototylomysphyllotis. M. RossLein, A1 Dufty, Jim Munger, Pete Bloom,Jeff Marks, Carl Marti and Ken Yasukawa made helpful suggestionson the manuscript.

LITERATURE CITED

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