Even Small Wooded Areas Good for Migrating Birds

First posted on 05-21-2010

When it comes to wooded spaces, birds aren’t too picky. Researchers at Ohio State University have discovered that even those small patches of woods left after urban expansions provide enough food and cover for migrating birds as they commute between their wintering and their nesting grounds.

“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 worked with colleague Paul Rodewald, an assistant professor of environment and natural resources at Ohio State, to produce the study.

The research focused on Swainson’s Thrush, a bird species that is closely related to the American Robin. These birds nest in Canadian forests, winter in Central and South America and pass through the eastern United States as they journey between locales.

Matthews and Rodewald captured close to a hundred Swainson’s Thrushes on the Ohio State campus as the birds migrated. They gently fitted them with miniature radio transmitters designed not to impede the birds in any way, and attached to them so that the transmitters would fall off naturally in a few weeks.

The birds were then released in small, wooded areas on campus. These sites varied in size from around 94 acres down to less than 2 acres. The transmitters allowed Matthews and Rodewald to track how long thrushes stayed in woodlots. Their expectation was that, if the birds left too soon, it meant the sites provided inadequate food and protection.

As it turns out, birds stayed the longest at the five largest sites in the survey, remaining until it was time for them to continue migrating north. At the two smallest sites, 28 percent of the birds moved into larger wooded areas in the region and the rest remained.

“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 stopover requirements within urban forest patches,” Rodewald said.

Matthews added that, “If our study sites differed strongly in habitat quality, we should have seen differences in how long the birds stayed. The fact that the stopover duration was similar suggests that all the sites were meeting the needs of the thrushes as they prepared for the next leg of migration.”

While admitting they could not simply apply the results to all birds, the researchers identified Swainson’s Thrush as one of the more forest-sensitive species and felt it was encouraging that they could make do even in small woodlots.

“These findings suggest that remnant forests within urban areas have conservation value for Swainson’s Thrushes and, potentially, other migrant landbirds,” Rodewald said. “Obviously, larger forest patches are better, but even smaller ones are worth saving.”

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