Species and study area

The Groove-billed Ani (Crotophaga sulcirostris) has a rare type of breeding system that sets the species apart from most other cooperative breeders. Breeding groups consist of two or more females and their mates. Females in these groups lay their eggs in a single nest and the joint clutch is cared for by all members of the group. This type of breeding system is known as joint-nesting plural breeding (Brown 1978). Plural breeders are species in which social units may contain two or more breeding females. Joint-nesting occurs when these females lay their eggs in a single nest. Other examples of joint-nesting plural breeders are the Acorn Woodpecker (Melanerpes formicivorus) and the Pukeko (Porphyrio porphyrio), which are discussed in Chapters 14 and 13, respectively. Those chapters and this one illustrate the considerable differences that exist among the species that share this breeding system, particularly in their mating systems and the numbers of non-breeding helpers.

Joint-nesting in the Groove-billed Ani probably did not evolve recently. The Smooth-billed Ani (C. ani), the Greater Ani (C. major) and the Guira (Guira guira) are also joint-nesting plural breeders (Davis 1940a,b, 1941; R. Macedo, personal communication). All four of these species are members of the Crotophaginae, in the family Cuculidae. Cuckoos have a range of breeding systems, including monogamy, polyandry and interspecific brood parasitism.