Over a period of three years, Stephen Matthews and Paul Rodewald of Ohio State University captured more than 100 Swainson’s thrushes on the university campus as they migrated through the area on their way to their breeding grounds in Canada’s boreal forests. They then glued tiny radio transmitters to the birds’ backs and released them at one of seven local wooded sites that ranged in area from less than one hectare to about 38 hectares.

By measuring how long the birds spent in the forest patches, they were able to determine whether the patches offered the food and shelter they required. At the five largest sites, the birds stayed until they left to continue their migration, while at the two smallest sites, less than 30 per cent of the birds moved to other sites in the region. The birds stayed, on average, for four days before moving on, with no difference in the length of stay across the sites.

‘If our study sites differed strongly in habitat quality, we should have seen differences in how long the birds stayed,’ Matthews said.

‘These findings suggest that remnant forests within urban areas have conservation value for Swainson’s thrushes and, potentially, other migrant land birds,’ Rodenwald added. ‘Obviously, larger forest patches are better, but even smaller ones are worth saving.’

July 2010