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Egg Losses in Communal Nests of the Guira Cuckoo

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Egg Losses in Communal Nests of the Guira Cuckoo J. Field Ornithol., 62(2):177-180 EGG LOSSES IN COMMUNAL NESTS OF THE GUIRA CUCKOO ROBERTOB. CAVALCANTI, MARISTERRA R. LEMES1, AND RENATO CINTRA 1 Departamentode Ecologia Universidade de Brasœlia 70970 Brasœlia,DF Brasil Abstract.--Communallynesting Guira Cuckoos(Guira guira) occurin permanentgroups of up to 18 individuals,suggesting a potential for strongcompetition among breeding adults. The patternof egglosses observed at three nestsin Brasilia,Brazil, is consistentwith the hypothesisthat breedingspaces are limited and groupmembers compete for spacein the nest.Marked eggsdisappeared from nestsand werefound, sometimes intact, under the nest. During laying, partial clutcheswere buried by additionsto the nestlining. The first eggs in the clutchwere the most susceptibleto disappearanceor burial. These resultsindicate that the Guira Cuckoohas reproductive strategies similar to otherspecies in the subfamily Crotophaginae. P•,RDIDA DE HUEVOS EN NIDOS COMUNALES DE G•JlRA G•IRA Sinopsis.--El cucogfiira (Guira guira) anida comunalmenteen grupospermanentes que alcanzanlos 18 individuos,1o que sugiereun gran potencialde competenciaentre los adultos que se reproducen.E1 patr6n de p•rdida de huevosobservado en tres nidosestudiados en Brasilia, Brasil, es consistentecon la hip6tesisde que los espaciospara reproducirseestrin limitadosy que losmiembros del grupocompiten pot espacioen el nido.Huevos que fueron marcadosdesaparecieron del nido y luegofueron encontrados, a vecesintactos, bajo el nido. Durante la •pocade puesta,parte de camadasfueron enterradas al afiadlrseleal nidonuevo materialde construcci6n. Los primeros huevos en la camadaresultaron set los mris suceptibles a desaparecero set enterrados.Estos resultados indican que el cucog/iira tieneuna estrategia reproductivasimilar a otrasespecies de las subfamiliaCrotophaginae. The anis (subfamilyCrotophaginae, Cuculidae) have a communal breedingsystem where several females lay eggsin the samenest (Wilson 1975:450-451). Competitionamong females for breedingspace has been documentedfor two of the four speciesin the subfamily.In this paper we presentindirect evidence for suchcompetition in a third species,the Guira Cuckoo(Guira guira). Anis are widelydistributed throughout South and Central America and occur as far north as Florida (de Schauensee 1970). Studiesof the Groove-billedAni (Crotophagasulcirostris) and the Smooth-billedAni (Crotophagaani) producedevidence of eggdestruction by birds of the breedinggroup (Loftin 1983, Vehrencamp1976). In Groove-billedAnis, egg-tossingwas performedby breedingfemales, and attributedto competitionamong them for the limited spacein the nest (Vehrencamp1977). Removalof eggsfrom communalnests by group membershas alsobeen reportedfor the Ostrich (Struthiocamelus) and the Acorn Woodpecker(Melaner•es formicivorus), and suggestedfor the • Presentaddress.' Departamento de Ecologia, Instituto Nacional de Pesquisas daAmazonia, Caixa Postal 4178,6901 ? Manaus, AM Brasil. 177 178] R. B. Cavalcantietal. J. Field Ornithol. Spring 1991 Pukeko (Porphyriop. melarzotus)(Bertram 1979, Craig 1980, Mumme et al. 1983). The Guira Cuckoo lives in open habitats in Brazil, Bolivia, Uruguay and Argentina (Sick 1985). It breedscommunally, and broken eggsare frequently found beneath nests (Davis 1940). Although these data are suggestive,they are not sufficientevidence of competitionfor spacewithin the nest.Here we reportegg losses that are consistentwith the hypothesis of destructionby group members. We studiedGuira Cuckoosin Brasilia, Brazil, where they occur in groupsof up to 18 individuals,which forage on the ground in farms, urban parks and gardens,and roost and nest in isolatedtrees. The sexes have identical plumage, and sexing requires capture and laparotomy, which we did not perform. The eggsare greenishblue with a relief of white calcifications,and vary in size, shapeand markings.We found nestswith up to 13 eggs,but were unable to ascertainthe number of laying femalesbecause eggs could not be assignedto discretecategories. We followednests daily during egg-laying,and on eachvisit marked all new eggsusing felt-tipped pens. We recordedegg destructionor burial at three clutches in two different nests. NEST I (TWO CLUTCHES) The first nestfound with a completeclutch on 14 Oct. 1983, at a height of 8 m in a Pinus oocarpa,and was rebuilt the following year. Twelve individuals,of undeterminatesex, were in the breedinggroup. The first clutch, found in early incubation,held 13 eggs,including four buried under the bottomlining of fresh green leaves.All eggsremained through incubation,but only sevenhatched, including one of the buried eggs, indicatinga significantconstraint on the ability of femalesto incubate large clutchessuccessfully. The secondclutch was foundon 17 Dec. 1984 with one egg. Betweenthis date and 27 Dec., we marked 11 more eggs on daily visits;eggs numbered 0, 1, 2, 8 and 10 disappearedduring this time. These are minimum estimates,because eggs laid and ejectedin less than a day may not have been detected.Marked eggshellswere found beneath the nest, in a pattern indicating breakage rather than predation of remains.No visitswere madebetween 27 Dec. and 12 Jan. 1985, and by then only four eggsremained, all previouslymarked, and the nesthad been abandoned. NEST 2 (ONE CLUTCH) The secondnest was found on 2 Feb. 1984 in an orchard, 3 m up in a mulberry (Morus sp.) tree. Eighteen Guira Cuckoos,unsexed, were in this group. The nest was discoveredwith one cold egg inside, and three freshlybroken eggs on the ground.Over the next 7 d, we marked 15 eggs in the nest, during daily visits except on 3 Feb. In the first 3 d, eggs numbered 1-4 disappeared;three were found under the nest tree (two whole, onebroken). A new lining was placedover the partial clutchbefore the last five eggswere laid; however,it was dismantledthe day after its Vol.62, No. 2 GuiraCuckoo Reproduction [179 reconstruction.Incubation began on 10 Feb., and lasted 11-12 d, during which eggs6 and 7 were buried by additionsto the nest lining. At least sevenyoung hatched,but four nestlingsdisappeared within a day of hatching,and may have been preyedupon by a group of Curl-crested Jays (Cyanocoraxcristatellus) foraging in the vicinity. Of the 15 eggs marked, four disappeared,two were buried, at least sevenhatched and only two youngfledged. Nest successis evenlower if we add the three eggsalready destroyed on the day the nestwas found. DISCUSSION Our resultsshow that in the Guira Cuckootwo or more eggscan be laid in a nestwithin 24 h, indicatingthat clutchesare apparentlylaid by severalfemales. The first eggsin the nest were the most susceptibleto burial or disappearance.This observationis consistentwith data of Veh- rencamp(1976) and Loftin (1983), where egg-tossingor burial were due to the activity of later-laying females.The high rates of egg lossin the secondclutch of Nest 1, and in Nest 2 could be due to unstable dominance relationshipsamong the femalesin the group, similar to thosedescribed for Groove-billedAnis (Vehrencampet al. 1986). Alternatively,Nest 1 couldhave been attacked by a revisitingpredator. However, size of egg remains on the ground and the lack of disturbanceat the nest site were not consistentwith the behaviorof predatorsin the area. Egg burial occurredthrough additions to the nestlining during laying or incubation.It affectedmostly the early eggsand thosenear the bottom, which also tendedto be the first-laid. Unlike egg-tossing,however, egg burial can be reversed(Loftin 1983). In the Guira Cuckoo, we observed both successfuland failed attemptsto bury eggsunder the nest lining. In the Smooth-billedAni, 37.3% of all eggslaid were buried,mostly during the initial statesof egg-laying(Loftin 1983). Early-laying femalesat- temptedto uncoverburied eggs,but were supplantedby late-laying fe- males (Loftin 1983). Our work demonstratesthat both egg ejectionand eggburial are com- monly used within the same speciesand within the same clutch. The frequent useof both strategiesby the Guira Cuckoodistinguishes it from the Groove-billedAni, which rarely usesegg burial, and the Smooth- billedAni, which rarely usesegg-tossing (Loftin 1983, Vehrencamp1976). Further studiesshould determine whether competition among breeding adults in the Guira Cuckoo is as prevalent as our work suggests,and whether nestlingcompetition is a strongforce reducingbreeding success in the group. ACKNOWLEDGMENTS This work was supportedby the ConselhoNacional de DesenvolvimentoCient•fico e Tecno16gico,through grants to RBC and scholarshipsto MRL and RC. We are grateful to H. Sick, R. Mac,do, R. Mumme, J. Hay, A Arafijo, E. H. Burtt, Jr. and refereesof thisjournal for helpful commentson the manuscript,and to S. Vehrencampfor suggestions on continuing the work. 180] R. B. Cavalcantietal. J.Field Ornithol. Spring 1991 LITERATURE CITED BERTRAM,B. C.R. 1979. Ostrichesrecognise their own eggsand discardothers. Nature 279:233-234. CRAIG,J. L. 1980. Pair and groupbreeding behavior of a communalgallinule, the Pukeko, Porphyriop. melanotus.Anim. Behav. 28:593-603. DAVIS, D. E. 1940. Social nestinghabits of Guira Guira. Auk 57:472-484. HAMILTON,W.O. 1964. The geneticalevolution of socialbehaviourß II. J. Theoret. Biol. 7:17-52. LOFLIN, R. K. 1983. Communal behaviorsof the Smooth-billedAni (Crotophagaani). Ph.D. thesis, Univ. Miami, Miami, Florida. MEYER DE SCHAUENSEE,R. 1970. A guide to the birds of South America. Oliver and Boyd, Edinburgh, United Kingdomß470 pp. MUMME, R. L., W. D. KOENIG,AND F. A. PITELKA. 1983. Reproductivecompetition in
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