Small patches of woods in urban areas valuable for migrating birds

WASHINGTON - A new research has found that even tiny patches of woods in urban areas provide adequate food and protection for some species of migrating birds as they fly between wintering and breeding grounds.

The findings are important because, with the expansion of cities worldwide, migrating landbirds increasingly must pass through vast urban areas which offer very little of the forest habitats on which many species rely.

“The good news is that the birds in our study seemed to be finding enough food in even the smaller urban habitats to refuel and continue their journey,” said Stephen Matthews, co-author of the study and a post-doctoral researcher in the School of Environment and Natural Resources at Ohio State University.

Matthews conducted the study with Paul Rodewald, an assistant professor of environment and natural resources at Ohio State.

The researchers published two related studies: one will appear in an upcoming issue of the journal Landscape Ecology and the other appeared in a recent issue of The Condor.

Both studies involved a secretive relative of the American Robin called Swainson’s Thrush (Catharus ustulatus). Swainson’s Thrushes winters mainly in Central and South America, and travel through the eastern United States to their breeding grounds in the boreal forests of Canada.

The researchers captured up to 91 Swainson’s Thrushes at a woodlot on the Ohio State campus while they were migrating through Columbus in May or early June, 2004 to 2007.

They then fitted them with tiny radio transmitters and released them at one of seven wooded sites in the Columbus area. (The radio transmitters were glued to back feathers and naturally fell off within a few weeks.)

The sites had forest sizes that ranged from less than one hectare (1.7 acres) to about 38 hectares (93.9 acres) in size.

Using the radio transmitters, the researchers tracked how long the thrushes would stay in the woodlots where they were placed. If they left soon after release, that would suggest that the sites did not provide the food and habitat that they required.

Results showed that at the five largest release sites, all the birds stayed until they left to continue to their migration north. At the two smallest sites (0.7 and 4.5 hectares), 28 percent of the birds moved to other sites in the Columbus region.

“The fact that a majority of the birds stayed at even our smallest sites suggests that the Swainson’s Thrushes were somewhat flexible in habitat needs and were able to meet their topover requirements within urban forest patches,” Rodewald said. (ANI)