This large, attractive cuckoo is one of the most social members of its family. Nesting groups are composed of two to four unrelated pairs that build a single nest in which all of the females lay their eggs. All of the individuals in the group participate in territorial defense, nest-building, incubation and food delivery. Adults are apparently incapable of recognizing their own eggs or nestlings, so the young are raised in communal clutches. Mating patterns and reproductive strategies within groups appear to be quite complex: though pairs are socially monogamous, extra-pair copulations with other group members are common, and unrelated, unpaired “helpers” may join nesting groups and attempt to reproduce as well. Females synchronize laying and compete with one another for reproduction by ejecting the eggs of fellow group members from the communal nest.
Greater Anis are widely distributed in lowland South America from Colombia to Paraguay, extending into Central America only as far as eastern Panama. Unlike its congeners, which favor open savannah and shrubby pastureland, the Greater Ani is found exclusively in forested habitats adjacent to water. It is most common along the edges of rivers and lakes, where it nests in emergent aquatic vegetation or in tree branches overhanging the water. The diet is composed mainly of terrestrial insects and the occasional small vertebrate, including katydids, dragonflies, spiders, larval lepidopterans, and anoles. Individuals usually forage in loose social groups, moving through the midstory along the water’s edge and gleaning large insects from the leaves and bark.
The unique natural history of the Greater Ani received little attention until recently, partly because nests are virtually inaccessible without a boat. The first comprehensive description of its habits and behavior was published by Davis (1941), who complained that “(e)ven though using a canoe at all times, it is frequently impossible to keep up with the birds or to follow them when they go into the thick brush or flooded lands along the river course.” (Davis 1941: 179). Though he was able to locate only one nest, Davis provided many important observations on the Greater Ani’s social habits and compared them with those of the other crotophagine cuckoos (Davis 1942). In 2007, a color-banded population of Greater Anis was established in Panama (Riehl and Jara 2009) and a set of polymorphic microsatellite markers was subsequently developed to allow genetic analysis of mating patterns and reproductive success (Riehl and Bogdanowicz 2009). Much of the information in this account is based on research in progress on this study population.