Territoriality and mating behavior of the male Brown-headed Cowbird

Abstract

The social behavior of 154 banded male Brown-headed Cowbirds (Molothrus ater) was studied at London, Ontario in 1966 and 1967. Aggressive encounters between them appeared to involve either the establishment and maintenance of a dominance hierarchy or the guarding of resident females. Dominant males mated with resident females in mostly monogamous relationships. Males occupied specific ranges but did not defend them. Dominant males, however, defended their mates, and females sometimes defended their males from other females. Excess males were present and in breeding condition. They attended any female during her mate's absence, courting and guarding her from advances by other males and occasionally copulating with her.