Interpret the interaction between a cowbird and a chipping sparrow as the sparrow raises the....?

Question

young of a brown-headed cowbird?

Answer 1

The cowbird benefits, clearly. The sparrow and its offspring lose slightly (more work, less food). More than slightly in lean times if one of the (smaller) sparrow chicks doesn't make it. And don't cowbird chicks toss out the host's chicks? It's been a while since I read up on this. Big-time downside there.

It is easy to see why the behavior persists from the cowbird's perspective. One can lay a lot more eggs and move on if the cowbird doesn't have to raise its chicks. Presumably the cowbirds get good selecting appropiate host nests (similar diet and size).

But from the sparrow's perspective? It may be that it is a minor problem in the whole being-a-sparrow spectrum of demands and that the overhead of sorting things out (bigger brain, less maternal instincts, etc) are too much of a handicap.

Or possibly the cowbird has only recently developed this strategy and the sparrow hasn't had time to adapt. Maybe more discerning sparrows are being selected for as we post.

I'd catagorize the relationship as host-parasite. I don't see how the sparrow beneifts at all.