Cooperative breeding, in which more than two individuals live in a social group and perform parental care of offspring (usually associated with a single nest), is rarely recorded in birds (Stacey and Koenig 1990, Koenig and Dickinson 2004). A review of cooperative breeding in diurnal raptors found at least one record of cooperative breeding in 42 of the 304 species considered (Kimball et al. 2003). These authors suggested that, independent of delayed dispersal of juveniles, cooperative breeding in diurnal raptors may be associated with: (a) intra- and interannual variability of resources; (b) a limited number of suitable nesting territories or nest sites; (c) benefits of group foraging to acquire food for young; (d) lack of individuals to form new breeding pairs; or (e) improvement in breeding success and nestling or breeder survival (Kimball et al. 2003).
Here, we summarize all reported observations that...