Cowbirds Sneak Out at Night from Host Parents' Nests to Learn New Skills

How does a cowbird know it's a cowbird? These birds are actually laid in the nest of different birds. Now, scientists are looking at how cowbirds know they're not a warbler, thrush or sparrow.

"If I took a chickadee and I put it in a titmouse nest, the chickadee would start learning the song of the titmouse and it would actually learn the titmouse behaviors," said Matthew Louder, one of the researchers, in a news release. "And then, when it was old enough, the chickadee would prefer to mate with the titmouse, which would be an evolutionary dead end."

The imprinting process is widespread among young birds and other animals. Brood parasites, though, like the cowbird, appear to be resistant to imprinting. They will imprint on a different species if confined with that species for an extended period of time in the cage, but don't do so in the wild.

In this latest study, the researchers look at prothonotary warblers, which cowbirds prey upon. Cowbird females are often spotted in the vicinity of cowbird nestlings, so researchers wanted to see whether or not the females led the nestlings away from their host parents at some point.

In order to track the birds, the researchers put radio telemetry transmitters on the cowbird nestlings and on adult female cowbirds in the forest where the host parents made their nests. The scientists took blood from the birds and conducted genetic analyses to match the juveniles to their biological mothers.

Tracking the birds, though, was next to impossible. That's when researchers switched over to an automated telemetry system. With this system, the scientists could track the location of each study bird.

So what did they find? Juvenile cowbirds actually did not follow female cowbirds. Instead, they left on their own after dark and returned the following morning to their host nests. In other words, the young cowbirds "sneak out" at night to learn skills before returning in the morning.

The findings are published in the journal Animal Behavior.

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