Mason Inman - science journalist

2008-02-11, 13:41:38

Cowbirds can act like mobsters, asking for "favors"—or else. These birds aren't looking for a cash payoff, but are trying to get other birds to raise their young.

The cowbirds lays their eggs in the nests of other bird species, and then come around to check on them later, to make sure the eggs are still there. If not, they'll trash the other birds' nests. (I covered these findings last year, in my article  "Mafia Birds" Make Others Raise Their Young ... Or Else.")

The cowbird chicks are rough on their nest-mates, emitting loud, high-pitched screeches so they get more attention—and more food—from the mother.

But a new study shows that the other nestlings don't just sit and take this. Song sparrow chicks fight back, matching the cowbirds' screams, which makes sure they get as much attention as the cowbird chicks. So even though the cowbirds are still exploiting the other birds, at least the song sparrows are able to keep up.

The parents may be getting stressed out by all the extra noise, though, since the researchers describe the parents as "harried."

Here's the abstract of the study, which will appear in the journal Proceedings of the Royal Society B:

Sheep in wolf’s clothing: host nestling vocalizations resemble their cowbird competitors

Like cuckoos, cowbirds lay their eggs in other birds’ nests.  Unlike in cuckoos, cowbird chicks do not hoist ‘host’ chicks out of the nest but instead attempt to outcompete them by emitting ear-splitting, high-pitch begging calls to monopolize their foster parent’s attention.  Rather than quietly accepting this, we show that when with a cowbird, song sparrow chicks match the cowbird’s screams to get their parents to pay attention to them.  This sheep in wolf’s clothing strategy seems to work because the harried parents do not neglect their own chicks.  Until now host chicks have simply been seen as passive victims.

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