Do cowbirds harm other birds?
The Eurasian cuckoo is far from unique, and of all the cuckoo-type birds on the western side of ‘the pond’, the brown-headed cowbird is perhaps best known. This brood parasite is equally crafty about raising its young without really raising its young. But it has a peculiar behaviour of its own. The female cowbird will stalk the host bird, such as a warbler, sparrow or blackbird, and to make sure she lays her egg at the right time, she may destroy its clutch or even the young or nest itself. This forces the host to start over, enabling the watching cowbird to lay in sync. Also unlike the Eurasian cuckoo, cowbird nestlings grow up alongside host chicks, but outcompete them. Nestling growth rates of the host may decrease due to the parasitic cowbird’s greater demands. If the host species is already under conservation pressure, this can have an impact.