The Wilson Journal of Ornithology 121(4):679–687, 2009 NATURAL HISTORY AND REPRODUCTIVE BIOLOGY OF THE COMMUNALLY BREEDING GREATER ANI (CROTOPHAGA MAJOR) AT GATU´ N LAKE, PANAMA CHRISTINA RIEHL1,3 AND LAURA JARA2 ABSTRACT.—The Greater Ani (Crotophaga major) is the least well-known of the communally breeding crotophagine cuckoos, although it is locally abundant in Panama and northern South America. We present substantial new life history information from 87 breeding groups of Greater Anis at Gatu´n Lake, Panama, and the first description of their conspicuous, highly stereotyped communal displays. Breeding groups were composed of two to five socially monogamous pairs; no pairs nested singly. Seven groups also included an unpaired individual, which in three cases was confirmed to be a 1-year-old male from the previous year’s nest. Groups of two and three pairs were most common (accounting for 75 and 20% of groups, respectively); groups containing more than three pairs were rare and their nests were abandoned before incubation began. Eggs were large (,17% of adult body mass) and varied greatly in size (19–37 g). Egg and nestling development were exceptionally rapid: eggs were incubated for 11–12 days and nestlings were capable of leaving the nest after 5 days, although adults continued to feed fledglings for several weeks. On average, each female laid 4.3 6 0.9 eggs; three-pair groups had larger overall clutch sizes than did two-pair groups. The first 2–3 eggs to be laid were usually ejected from the nest by other group members, and number of ejected eggs increased with group size. Thirty-seven nests (43%) fledged at least one young successfully; snakes (Pseustes, Spilotes, Boa) and white-faced capuchin monkeys (Cebus capuchinus) were identified as nest predators. Received 27 January 2009. Accepted 4 June 2009. The subfamily Crotophaginae (Cuculiformes: Females in each group compete for reproduction Cuculidae) consists of four species of communal- and synchronize laying by ejecting each others’ ly breeding neotropical cuckoos (Davis 1942). eggs from the communal nest (Vehrencamp and Three of the four species have been subjects of Quinn 2004). long-term behavioral studies: Groove-billed Ani Reproductive strategies within this general (Crotophaga sulcirostris) in Costa Rica (Vehren- framework differ markedly among the three camp 1977, 1978; Vehrencamp et al. 1986; species that have been well studied. Groove-billed Koford et al. 1990); Smooth-billed Ani (C. ani) and Smooth-billed anis are facultatively commu- in Florida and Puerto Rico (Davis 1940, Loflin nal: breeding groups can consist of lone pairs, 1983, Quinn and Startek-Foote 2000, Schmaltz et multiple monogamous pairs, or multiple pairs al. 2008); and Guira Cuckoo (Guira guira)in with a variable number of non-breeding helpers Brazil (Macedo 1992; Cariello et al. 2002, 2004; (usually retained young from a previous brood; Macedo et al. 2004). Several individuals (both Bowen et al. 1989). The modal group size is two males and females) in all three species cooperate pairs and behavioral observations suggest that to build a single nest in which all of the females extra-pair copulations are not common within lay their eggs. Young generally disperse to join groups (Vehrencamp et al. 1986). Only early-laid nearby groups rather than remaining with the natal eggs are ejected from the nest, probably because group to breed; thus, adult breeders in groups are females are incapable of recognizing their own thought to be unrelated (Quinn et al. 1994, eggs and cease ejection once they enter the laying Vehrencamp and Quinn 2004; but see Bowen et sequence. As a result, early-laying females lose al. 1989). Most group members participate in more eggs to ejection than late-laying females nest-building, territory defense, parental care, and (Vehrencamp 1977). incubation (although relative effort may differ Guira Cuckoos nest in larger groups containing greatly among group members), and most females up to seven reproductive females; lone pairs are appear to fledge roughly equal numbers of young. rare (Macedo et al. 2004). Pairs are not socially monogamous and each individual may mate with 1 Princeton University, Department of Ecology and several group members, leading to genetic poly- Evolutionary Biology, 106A Guyot Hall, Princeton, NJ gynandry. Females compete for reproduction in 08544, USA. the nest by both egg ejection and infanticide of 2 Universidad de los Andes, Departamento de las Ciencias Biolo´gicas, Carrera 1A Numero 18A-10, Bogota´, nestlings. Unlike anis, Guira Cuckoos eject eggs Colombia. throughout the laying sequence, presumably 3 Corresponding author; e-mail: [email protected] because females are more likely to begin laying 679 680 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 121, No. 4, December 2009 asynchronously in larger, less well-organized study area, within the 5,400-ha Barro Colorado groups. Eggs of both early and late-laying females Nature Monument, consisted of the 65-km may be ejected, and female laying order changes shoreline of Barro Colorado Island and its between clutches. The number of eggs that each associated smaller islands, as well as an additional female loses to competition varies from clutch to ,300 km of shoreline along four adjacent main- clutch, and female reproductive success tends to land peninsulas (Bohio, Buena Vista, Pen˜a equalize within groups over time (Macedo 1992, Blanca, and Gigante). Barro Colorado Island and Macedo et al. 2004). the mainland peninsulas are covered by tropical Little is known about the Greater Ani (C. moist forest (Holdridge et al. 1971) and are deeply major). Conspicuous and locally abundant from dissected by narrow, sheltered coves. Shoreline eastern Panama through northern Argentina, it vegetation within these coves is dominated by nests exclusively along the forested banks of Annona glabra, a small tree that grows in the lakes, rivers, and streams (Hilty and Brown 1986). water along the shore, and Acrostichum danaeifo- Nests are built in emergent vegetation or in lium, a large aquatic fern (Croat 1978). Rainfall branches overhanging the water, and are usually averages 275 cm annually and is strongly season- accessible only by boat. Young (1925) and Davis al with a marked dry season lasting from mid- (1941) each provided brief descriptions of one December through late April (Rand and Rand nest (from Guyana and Argentina, respectively), 1982). We searched for Greater Ani nests during and noted that this species appeared to live in the rainy season (May–Nov) by moving slowly social groups similar to those of its congeners. along the shoreline in a small motorboat, More recently, Lau et al. (1998) located 27 nests following adults and checking emergent vegeta- along Caracol Creek, Venezuela. They found that tion. nests built in isolated clumps of emergent Color Banding and Group Size Assessment.— vegetation were significantly less likely to be We captured adult anis at communal roost sites depredated than those built along the bank, (during the non-breeding season) and near nests presumably because the most likely predators (during the breeding season) using 61-mm mesh were terrestrial rodents and wedge-capped capu- mist nets (12 m length) on 5-m aluminum poles. chin monkeys (Cebus olivaceus). Nets were mounted in shallow water parallel with Many aspects of the natural history of the the shore to capture birds as they flew across the Greater Ani remain unknown, including clutch water. We used kayaks in areas with deeper water size, parental behavior, egg morphology, and (.1 m) to erect the nets and remove birds from length of incubation and nestling periods. Basic nets. Nets were monitored constantly during information is also lacking on its communal trapping and birds were removed immediately breeding system, including size of nesting groups upon capture. Each ani was banded with a unique and extent of egg ejection. It is not known combination of three color and one aluminum leg whether communal nesting is obligate or faculta- bands for individual recognition. tive in this species, nor whether individuals within Group size was calculated by counting all groups form socially monogamous pairs. Our goal adults present at each of at least three visits to the in this study was to provide data on these nest. All group members defend the nest and previously unrecorded life history traits through participate in communal displays in the nesting field observations of a color-banded nesting territory; group size counts were consistent and population of Greater Anis. We also wished to highly repeatable (estimate based on 3–8 counts at investigate the highly stereotyped, conspicuous each of 85 nests: R 5 0.84, F84,170 5 182.0, P , social displays performed by breeding groups. 0.0001; Lessells and Boag 1987). Groups typical- This communal display has not been described in ly consisted of socially monogamous pairs, so the the literature aside from a brief mention by number of breeding females in the group was ffrench (1973). assumed to be half the total number of individuals in the group. The ‘‘extra’’ individual was assumed METHODS to be a juvenile non-breeding helper in the few Study Area.—We studied Greater Anis in 2007 groups that consisted of an odd number of and 2008 at Gatu´n Lake, Panama, an artificial individuals (Loflin 1983, Quinn and Startek-Foote reservoir formed in 1914 when the Chagres River 2000, this study). The number of breeding females was dammed to create the Panama Canal. Our was assumed to be half the remaining group size Riehl and Jara N BREEDING BIOLOGY OF GREATER ANIS 681 (for example, a group of 7 individuals was Nest Cameras.—We installed digital motion- assumed to contain 3 breeding females). Evidence activated nest cameras (Wingscapes BirdCams, from the other Crotophaga spp. (Vehrencamp 1977, Alabaster, AL, USA) at 17 nests to identify Loflin 1983) as well as from this species supports diurnal nest predators and to test pilot methods for the assumption that all adult female group members future nest monitoring.