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 stopover requirements within urban forest patches," Rodewald said.
The study revealed that the birds stayed at each site from one to 12 days, with the average being about four days. There was no difference in how long the thrushes stayed across the seven sites.
"If our study sites differed strongly in habitat quality, we should have seen differences in how long the birds stayed," Matthews said. "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."
The study did find that the later the calendar date, the shorter the thrushes stayed at the sites. That may be because the later-arriving birds would be in more of a rush to reach their breeding grounds, Matthews said.
Weather was also a factor: birds tended to leave the sites when winds were light, following a drop in barometric pressure.
Birds also tended to stay longer if they had lower body mass, suggesting they needed to bulk up more to continue their journey.
While nearly all sizes of woods appeared adequate for the thrushes, they still seemed to prefer larger forested areas, the study revealed.
In one of the studies, the researchers found that in the larger urban woodlots, the thrushes would stay farther in the interior and not get a
|Contact: Stephen Matthews|
Ohio State University