Evolution and life-history correlates of female song in the New World blackbirds

Female song is much more prevalent in tropical than in temperate songbirds but, we know surprisingly little about the evolutionary origins of this striking latitudinal difference. Here I reconstruct the evolution of female song in the New World blackbird family (Icteridae) and compare historical changes in this trait to changes in several other life-history characters: social mating system, nesting pattern, and migratory behavior. Reconstructions using both parsimony and maximum likelihood methods show that female song has been lost repeatedly in this clade and that tropical ancestors with frequent female song almost invariably were monogamous, had dispersed nest sites, and were nonmigratory. Losses of female song were not consistently associated with changes in any single life-history characteristic across the family, but rather appear to have occurred for different reasons in different lineages, including the evolution of migration in the oriole genus (Icterus), the evolution of brood parasitism in the cowbirds (Molothrus), and the evolution of polygynous, colonial breeding in the oropendolas (Psarocolius, Gymnostinops) and caciques (Cacicus). These results support previous suggestions that the prevalence of female song in the tropics is largely explained by the life-history traits associated with tropical habitats. Copyright 2009, Oxford University Press.