A paper titled "Out on their own: A test of adult-assisted dispersal in fledgling brood parasites reveals solitary departures from hosts" and published in the journal Animal Behaviour has established that young cowbirds leave their parents in the evenings, spend the night in the fields, and return to their mothers just before sunup.
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The study was supported by the Animal Behavior Society, American Ornithologists' Union, Illinois Natural History Survey, Illinois Chapter of the Nature Conservancy, Illinois Department of Natural Resources and the U.S. Fish and Wildlife Service.
The study was led by Matthew Louder, a postdoctoral researcher with East Carolina University in North Carolina and Hunter College in New York, and Jeff Hoover an INHS biological surveys coordinator Wendy Schelsky. They wanted to find out if a juvenile cowbird identifies it is a cowbird after it develops from an egg put in a warbler’s, sparrow’s, or thrush’s nest.
"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. "And then, when it was old enough, the chickadee would prefer to mate with the titmouse, which would be an evolutionary dead end."
The juvenile cowbirds were found not to imprint on their host parents, a process whereby birds tend to mate with other species with whom they grew with in the same nest.
The researchers also wanted to know if cowbird moms lead their young out of the forest, after finding through a previous study that cowbird females do not leave their eggs in another species nest, and always return to ensure their young survive even in another species nests.
So a young cowbird was fitted with radio telemetry transmitters so that it can be tracked in the forest and prairie, and its blood sample was taken to analyze its genes with its biological mother. But the experiment didn’t prove too successful until Michael Ward, a professor of natural resources and environmental sciences at the University of Illinois came around to help track the birds.
He helped construct an automated telemetry system," Louder said. "We put up three radio towers, each with six antennas on it, so you have 360-degree directional coverage. All three towers track one individual cowbird at a time and then move to the next individual."
This helped Louder monitor the birds under observation round the clock, and it was eventually found that juvenile cowbird don’t follow their mothers out into the forest in daylight, but then they sneak out alone in the night and then return at the first sign of sunlight the next morning.
"Clearly, there's a lot more to these birds than people would have thought," Hoover clarified. "We still have more layers to peel away from this onion that is the cowbird."