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SULLIVAN. 1993. Sea- AssociateEditor: J. S. Sedinger The Auk 116(3):847-851, 1999 Confirmation of Infanticide in the Communally Breeding Guira Cuckoo REGINA H. F. MACEDO 1,3AND CELINE MELO 2 lDepartamentode Zoologia, Universidade de Brast'lia, 70910-900 Brast'lia, DF, Brazil; and 2DepartamentodeBioci•ncias, Curso de Ci•ncias Bioldgicas, Universidade Federal de Uberlgndia, CampusUmuarama, 38405-320 Uberlgndia, MG, Brazil The killing of conspecificinfants may be common namics.For example,despite the appearanceof so- (Hrdy 1979, Sherman 1981, Hrdy and Hausfater cial monogamy,the Guira Cuckoomating system in- 1984,Parmigiani and Vom Saal1994) but is reported cludespolyandry and polygyny (Quinn et al. 1994). infrequentlybecause the behavioroccurs rapidly. In Additionally,breeding opportunities may be limited several speciesof mammals, infanticide has been becausesome group members are excludedfrom re- linked with mate takeover or cases where a new production.Circumstantial evidence has suggested dominant male comes into contact with infants sired that the killing of newlyhatched chicks is a common by the harem'sprevious male (Hausfateret al. 1982, occurrenceand that high chickmortality probably Sommer1994). In birds,infanticide usually has been resultsfrom infanticideby conspecifics(Macedo and reportedin the contextof siblingrivalry (Mock1984, Bianchi1997b). In this paper,we confirmthat infan- Fujioka 1985, Drummond et al. 1986, Mock and ticide is indeed an important causeof mortality for Forbes1994), althoughevidence suggests that the Guira Cuckoonestlings, and we speculateabout its killing of infantsalso may increasethe perpetrator's function as a reproductivestrategy. fitness by decreasing a competitor's reproductive Methods.--Thestudy was conducted in a suburban successor enhancingaccess to a potentialmate (Trail area of Brasilia, Brazil (15ø47'S,47ø56'W; elevation = et al. 1981,Stephens 1982, Stacey and Edwards1983, 1,158m), from September1995 to March 1996and Fujioka 1986). September1997 to February1998; these periods co- Guira Cuckoos(Guira guira) occur in groupsof as incidewith the rainy seasonin this region.Further many as26 individuals(Gallardo 1984) and are clas- descriptionof the study site and vegetationcan be sifiedby Brown (1987)as plural breederswith joint found in Macedo(1992). Each active nest was visited nests. During reproductive periods, groups are dailyto checkfor neweggs, and the groundbeneath smallerbut still may includeas many as 13 adults. thenesting tree was searched for vestigesof anyeggs Throughoutthe egg-layingand incubationperiods, or chicksnot in the nest.On the first or seconddays eggsare commonlytossed out of the nest by group posthatching,each chick received temporary colored members(Macedo 1992). After chickshatch, group leg bandsmade out of plasticdrinking straws,or col- membersdo not participate equitably in nestling ored dye marks. Continuousperiods of nest obser- feedingor nestguarding (Macedo 1994). DNA anal- vationswere conductedprimarily during the first ysis has shedlight on severalaspects of groupdy- week after chickshatched (the period when nestling disappearanceis mostprevalent). Group sizewas es- E-mail: [email protected] timatedby countingthe adultsaround the nestat 848 ShortCommunications [Auk, Vol. 116 TABLE1. Fatesof eggsand chicksin 15 communalnests of Guira Cuckoosduring two nestingseasons. Rangesare in parentheses. Variable 1995-96 1996-97 g +_ SD No. nests monitored 7 8 -- Total eggslaid 65 85 -- Total eggslost 11 41 -- Totaleggs hatched 41 53 -- Total chicks lost 24 30 -- No. eggslaid per nest 9.3 (6 to 13) 10.6 (6 to 21) 10.0 _+3.8 No. eggslost per nesta 1.6 (1 to 4) 1.5 (0 to 9) 1.5 _+2.3 No. eggshatched per nest 6.8 (4 to 12) 6.6 (2 to 10) 6.7 _+2.7 No. nests with chick losses 6 7 -- No. chickslost per nest 4.0 (1 to 7) 3.8 (0 to 7) 3.9 _+2.5 No. observed infanticides 2 4 -- Overall chickslost (%) 58.5 56.6 57.5 Egg lossfrom tossingby cuckoosor disappearancewith causeunknown. eachvisit andduring observation periods; three con- Infanticide3, nestC16.2.--0n 13 November 1995, sistent maximum counts were needed before an es- we observedan adult approachthe nestat 1235,pick timate was consideredadequate. Adult group mem- up a live four-day-oldnestling, and carry it to the berswere capturedand colorbanded whenever pos- groundabout 35 m from the nesttree. It peckedthe sible. nestlingrepeatedly for about1 min andthen left. The Results.--We monitored 15 successfulnests (i.e. at chick was examined immediately afterwards and least one chickhatching) from egg laying until at wasdead, although without visible external wounds. leastthe eighth day after hatching.The numberof Group size at this nestwas five adults. eggslaid per nestin bothyears averaged 10.0 _+ SD Infanticides4 and 5, nestFlbl.--The infanticide of 3.8; egg lossper nest averaged1.5 _+2.3 (Table1). events at this nest occurred on 28 December 1995, Additionally,chicks disappeared from 13 nests(g = when the nestlingswere six daysold. Our evidence 3.9 -+ 2.5), with more than half of the hatchedchicks was circumstantial in one case: we found a dead nes- dyingwithin the first week.Group size averaged 6.4 tling on the ground,about 10 m from the nest,with adults(range 4 to 8) for the sevengroups observed. hematomasaround its eyes.We founda live nestling We observedeight infanticidesduring the study pe- on the groundat 1530,but we did not seeit being riod and had circumstantial evidence for an addi- evictedfrom the nest.For about30 min, a groupof tional two cases.Below, we detail these10 cases(nest sevenadults vocalized near the nesttree. Gradually, codingmatches other published work), two of which four of them approachedthe nestlingand peckedit are not includedin Table1 owing to lack of nesting violentlyfor a shortperiod of time.At 1800,when the data (nest Flbl). observationperiod ended, the nestlingwas alive but Infanticide1, nestA8.2.--On 31 October 1995, at motionless.Group size was sevenadults. 1115,an adultwent to the nest,picked up a two-day- Infanticide6, nestB9.1.--At 1025on 2 October1997, old nestlingwith its beak, and flew to the ground an adult went to the nest,picked up a three-day-old some 30 m away from the nest tree. Three other chick,and carriedit to a perchon a fenceabout 10 m adults approached,and for approximately1 min, from the nesttree. The chickwas alive and moving. theyall peckedand pulled on the chick.The nestling Anotheradult flew from the nesttree and joined the was still alive at 1500, at which time it showed no ex- first one. The first adult dropped the chick to the ternal woundsbut was barely moving.The adults ground,and after about1 min, both adultsflew away did not approachthe chick after the initial attack. from the area. When the chickwas inspectedabout Groupsize at this nestwas eight adults. 5 min later, it was dead and showed no external Infanticide2, nestA8.2.--A secondcase of infanti- wounds.Group size at this nestwas eight adults. cide occurredat nest A8.2 at 1205on the sameday, Infanticide7, nestC16.1.--This episode occurred at 31 October1995, when an adult approachedthe nest, 1619 on 8 October 1997. An adult flew to the nest, pickedup a secondnestling, and tossedit overthe pickedup a one-day-oldnestling, and flew to the nest rim. This adult, along with two others,pecked groundabout 10 m from the nesttree. It peckedthe and pulled on the nestlingfor about 1 min before chick repeatedly,then picked it up and flew away abandoningit. Upon examination10 min after the from the area.Group size at this nestwas four adults. event, the chick was dead and exhibited two abdom- Infanticides8 and 9, nestB8.2.--At 1250 on 16 No- inal punctures.At 1415,an adult took food to the re- vember 1997, an adult picked up a live one-day-old maining nestlingsand then approachedthe dead nestlingand flew to a tree approximately40 m from chick,pecked it repeatedly,and tossedit in the air. the nest. We were unable to determine whether it July1999] ShortCommunications 849 droppedthe nestlingor flew awaywith it. Laterthat at leastone other adult was in closeproximity to the day, a dead nestlingwith severalhead woundswas one that evictedthe chick,or helpedto attackthe found at the baseof the nest tree. Group size was chickafter it had been evicted.We observedno ag- eight adults. gressionamong adults, and it is very unlikelythat a Infanticide10, nestD3.2.--On 9 December1997, a groupof nonresidentindividuals could approach the marked adult group memberpicked up a one-day- nestand evict chickswithout beingattacked by the old nestlingand carriedit to a fenceabout