It depends upon your point of view. The cowbirds grow faster, and will actively work to shove all of the other, smaller, nestlings out of the nest to their death. So, the smaller birds usually "leave" the nest first, with the remaining cowbird becoming the last to leave the nest.

ETA: They will also hatch sooner and will push the other eggs out of the nest. Of course, it depends some on the configuration and species of the nesting birds. If the nest is too deep in a cavity for sibling removal, the much larger cowbird will demand most of the food, and the smaller birds often die from neglect and bullying.

Thanks gyr_falcon.

Audubon has an interesting article; Is It Okay to Remove Cowbird Eggs From Host Nests? The short answer is no.

Claire

I read about a study that revealed cowbirds also monitor the nests where they have laid their eggs. The gist was, if the youngster (or those of other cowbirds) is raised successfully, they are more likely to reuse that nest in the future. If the youngster fails to survive, they are less likely to use that nest again. So the section at your link about retaliation is more understandable, Claire, than in the oft-assumed scenario where the cowbird lays an egg and then abandons all responsibility.

It certainly seems as if the cowbirds have lost the nest-building and nestling feeding instincts but still retain the instinct to protect their young. That makes sense in terms of survival of the species.

I've noticed here that the young cowbirds that were raised by other birds all manage to find each other and flock together after they fledge.

Nature has more options than we assume.

Claire

I've read that cowbirds developed the necessity of laying eggs in other birds' nests because they followed the migration of bison across the plains. I've also read articles that refute this theory.

gyr_falcon, but wouldn't that mean that their behavior of using other nests for their eggs so they could follow the bison, be impossible......if they hung around to see if their young survived, so they could use the same nest next year?

I have not heard the bison theory before. The bison's native range didn't include my area of the country, even though we are in the cowbird's native range. While it is possible for the same species to have different behaviors in different regions (purple martin nesting habits in the east vs. west, for example), it would seem if bison were the reason for the behavior coming to be, it might exist only where bison ranged, and in non-bison regions the cowbirds would make nests.

Hmmm......I had never thought of their behavior in areas without bison. (or maybe originally, there were bison everywhere??) Much food for thought!