It adds, "In contrast, catbirds and robins, which lay unmarked blue eggs, almost invariably eject cowbird eggs from their nests." Gray catbirds are another exception, according to Audubon.

Many species of birds get reputations of various sorts. One species that gets a bad rap, through no fault of its own, is the brown-headed cowbird. The female cowbird lays its eggs in the nests of ...

Because cowbird eggs require a shorter incubation period—and female cowbirds can lay more eggs than most wild birds—their chances of survival in host nests surpass that of the host’s own young.

The instinct to incubate whatever eggs a nest contains is powerful, but some birds can recognize cowbird eggs. Catbirds and robins, for example, remove cowbird eggs from their nests.

This purple finch nest with four finch eggs and one from a brown-headed cowbird, a notorious brood parasite. Photo courtesy of Tom Tatum ...

The female cowbird watches other birds construct their nests, and after eggs are laid there, she sneaks in to lay one of her white, speckled eggs. Often, the cowbird ejects an egg from the host nest ...

The next time I checked our finch nest, I was surprised to find the cowbird egg was gone, as was one of the finch eggs, leaving just three finch eggs in the nest. The intrusive cowbird youngster ...

However, one exception is the freeloading Brown-headed Cowbird, laying its eggs in the nests of other birds, a behavior known as nest parasitism.

When the study nests contained between 3 and 4 warbler eggs, Mr Antonson and his collaborators experimentally parasitized the nests by adding a newly-laid cowbird egg from a different nest.

"We focused on what happens when a cowbird hatches into a nest with different numbers of host nestlings." Cowbird chicks never eject eggs from host nests or directly kill host young.