Host birds sometimes notice the cowbird egg, to which different host species react in different ways.

They moved eggs around so that 20 nests each had one cowbird egg.

If the cowbird egg is removed, the female cowbird may destroy the host's eggs.

Each parasitized nest contained 1 brown-headed cowbird egg.

Two of the five brown-headed cowbird eggs produced fledglings.

Upon recognizing a cowbird egg in its nest, the warbler will often smother it with a new layer of nesting material.

The number of young produced by the hosts that ejected eggs dropped 60% compared to those that accepted the cowbird eggs.

They can also recognize and remove cowbird eggs from their nests.

However, the Robin usually rejects the cowbird eggs.

The Robin usually rejects the cowbird eggs.