A Tale of Two Nests

Clockwise from upper left: Pastel blue eggs and speckled eggs in nest near Hay Harbor Club golf course, Quintin Parsons Photo; hatchlings emerge from speckled eggs, Quintin Parsons Photo; robin hatchlings calling for food on Penni’s Path near Driving Range, Caroline Yerkes Photo; robins hatch, Caroline Yerkes Photo

The above photos tell an all too common story in nature of opportunism, destruction and survival of the fittest.

The speckled eggs in top left photo were laid by a brown-headed cowbird, an opportunistic “brood parasite” that lays eggs in nests built by other birds. When the female is ready to lay eggs (up to 40 in a season), she looks for any nest built by over 200 species of other birds. She usually removes one of the other bird’s eggs, lays her own and expects the host female to raise the cowbird young.

Sometimes, when the host female returns to the nest, she will remove the cowbird eggs. But the cowbird often keeps watch on the invaded nest and will retaliate by destroying all of the host female’s eggs, which never stood a chance against the young cowbirds.

Cowbird hatchlings are larger and more aggressive than the host’s young. They develop rapidly and demand more food, pushing the host’s young from the nest to perish, ensuring they will get all the food to survive. The baby cowbird is then raised by the unsuspecting host bird and leaves the nest in 10-11 days.

This invasion of the nests of other species has been bad news for other songbirds. The heavy parasitism of cowbirds, according to Audubon Guide to North American Birds, has pushed some species to the status of “endangered”.

Now for the second nest in the bottom two photos: Good news! Unhampered by an invasion from the brown-headed cowbird, these robin hatchlings have an excellent chance of surviving.