Juvenile Cowbirds Sneak Out of the Nest at Night to Avoid Imprinting

Posted on November 7, 2015

Juvenile cowbird with tracker

Cowbirds are left as eggs in the nests of different species. They are then raised by their unsuspecting host parents. The cowbird is somehow able to avoid imprinting on its host. It lives life like a cowbird when it is an adult and not the host bird, such as a warbler or sparrow.

Researchers from the University of Illinois have figured out how the juvenile cowbirds may avoid imprinting on their host. The researchers monitored juvenile cowbirds and found that they sneak out of their nests at night and spend them in nearby fields all alone. They return to the nest just after daybreak. The researchers believe this unusual behavior likely plays a role in helping the cowbirds avoid imprinting. Cowbirds will imprint on a host species if left in a cage with it in a lab type of setting but they do not imprint in the wild, likely due to this unique behavior.

Matthew Louder conducted the study as a Ph.D. student with Illinois Natural History Survey avian ecologist Jeff Hoover and INHS biological surveys coordinator Wendy Schelsky. Louder says in a statement, "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."

Cowbirds have to learn how to eat like cowbirds because they have a different diet then their hosts. For example, cowbirds eat seeds for about 3/4 of their diets while warblers eat primarily insects.

The researchers monitored the birds using trackers and an automated telemetry system. This is how they discovered the birds were leaving the forest for the fields at night and then sneaking back in. The researchers still don't know how cowbirds find their way into a cowbird flock where they learn cowbird social skills. They did find some evidence of vocalizations between the cowbird juveniles and cowbird mothers. The mothers are also sometimes spotted in the vicinity of cowbird nestlings.

The research paper was published here in the journal, Animal Behaviour.

Photo: Mike Ward