Conspicuous female plumage is common among open cup-nesting passerine birds

Abstract

Alfred Russel Wallace hypothesized that the use of cavity or dome nests releases incubating birds from predation risk, and that this allows the evolution of conspicuous coloration in females. By this hypothesis, females that use open nests are subject to strong selection for crypsis. Here, we test the validity of Wallace’s proposed evolutionary correlation between nest type and conspicuous coloration in females across the largest avian radiation, the Passeriformes, using phylogenetic comparative methods. We also test an alternate hypothesis that cavity-nesting results in greater conspicuousness because competition for cavities is stronger than for other nest sites, and such competition can drive social selection on female plumage. By this hypothesis, dome-nesting females should generally be less conspicuous than cavity-nesting species. We found no support for Wallace’s hypothesis that concealed nests yield conspicuous plumage while open nests yield dull plumage, and some support for the social selection hypothesis in smaller-bodied, gregarious species. While our analyses do not support the core part of Wallace’s hypothesis, they corroborate his contention that evolutionary transitions in nest type are rare, indicating that nest types may influence macroevolutionary selective regimes for other traits.