The Adaptive Basis of Geographic Variation in Color of the Purple Martin

Abstract

Geograpnic variation in morphology in the purple martin (Progne subis) involves both size and color, with the exception that adult males show no color variation. Martins from the southwestern North American deserts are pale and small; martins from the mountains and the north and east are darker and larger. Color of the feather coats of females and 1st-year males is thought to be both cryptic and of value in regulating heat flow between the bird and its environment. The uniform color of adult males from all sectors of the range of the species presumably reflects selection for display plumage in accord with Darwinian sexual selection.