Noisy Intruders

By late April, some songbirds, such as robins and mourning doves, are already nesting.  Their parental activity will soon be mimicked by summer residents arriving from the south.  Indeed, birdsong is beginning to peak, reflecting the mating behavior of our many avian neighbors.

Joining this chorus are the varied tunes, squeaks and rattles of brown-headed cowbirds.  Settling in suburban shade trees, these noisy visitors survey the activity of other songbirds but do not construct nests themselves.  Rather, after mating, the female cowbird lays her eggs in the nests of other birds, generally leaving one egg in each parasitized nest; she is then free to mate again and may produce several clutches before late summer.  Unfortunately, the young cowbirds are often larger and more aggressive than the offspring of their adoptive parents, garnering much of the food and sometimes shoving their hapless cohorts from the nest.

In light of this behavior, many birders despise cowbirds; after all, it's hard to admire a species that shirks its parental duties and threatens the welfare of other species.  But nature does not judge her creatures and this instinctive reproductive behavior has made the brown-headed cowbird a very prolific and successful resident of many North American ecosystems.