Tree Swallow (Tachycineta bicolor) Science Article 1
Females, and not males, have delayed plumage maturation. The hypothesis that plumage differences are the result of differences in competitive abilities among individualsis tested by comparing brown and blue Tree Swallow females in terms of foraging abilities, as determined by the growth of nestlings under their care without the help of the males, and in terms of body size and nutritional condition.
GEORGE A. LOZANO AND PAUL T. HANDFORD, Wilson Bull., 107(l), 1995, pp. 153-164