Brown-headed Cowbird: Dr J Murray Speirs

Brown-headed Cowbird (male)

Cowbirds are fascinating birds, wholly dependent on other birds to incubate their eggs and raise their young. Then how do they come to know that they are cowbirds, having been raised by a Yellow Warbler or a Song Sparrow or some other species? Yet when fall comes they flock with their own kind and associate with other blackbirds. How do they know that they are blackbirds? when they have bills that might class them with finches or sparrows? Banding has shown that they have strong homing tendencies, but why, when other species raise their young and you might think they no need to establish a home base?

Brown-headed Cowbird

Most of our birds arrive with other blackbirds in early spring and the males are soon displaying, puffing themselves up, then bowing so low they almost overbalance. When other birds start nesting, the unobtrusive female cowbirds find many nests and deposit eggs in them, laying for several weeks. One lady, who had phenomenal success in finding nests, attributed her success to following female cowbirds around. Most of our birds go south to the United States in winter but a few may be found in Southern Ontario then. Peck (1981) listed 84 species that have been parasitized in Ontario by cowbirds, with Yellow Warbler, Song Sparrow and Chipping Sparrow the chief hosts.

Brown-headed Cowbird (female)

Males are black birds with brown heads, somewhat larger than House Sparrows, but quite similar in build. Females are blackish gray, the amount of black varying considerably. The young are gray, streaked with dusky: they make their presence known by incessant, loud, somewhat buzzy food calls. Adults utter “see-tu-tu” and have a lip-smacking sputter when they take off in flight.

Cowbird (male) Photo: Ken Sproule

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