Even bird brains can get to know an entire continent -- but it takes them a year of migration to do so, suggests a Princeton research team.
The scientists have shown that migrating adult sparrows can find their way to their winter nesting grounds even after being thrown off course by thousands of miles, adjusting their flight plan to compensate for the displacement. However, similarly displaced juvenile birds, which have not yet made the complete round trip, are only able to orient themselves southward, indicating that songbirds' innate sense of direction must be augmented with experience if they are to find their way home.
"This is the first experiment to show that when it comes to songbird migration, age makes a difference," said team member Martin Wikelski, an associate professor of ecology and evolutionary biology. "The results indicate that the adult birds possess a navigational map that encompasses at least the continental U.S., and possibly the entire globe."
Two longstanding questions about migrant songbirds are how quickly they recover when thrown off course -- as they can be when they encounter powerful winds -- and just what navigational tools they use to do so. To address the two questions, the team decided to fit a group of white-crowned sparrows with tiny radio transmitters no heavier than a paper clip and track their movements from a small plane.
The team first brought 30 sparrows to Princeton from northern Washington state, where the birds had been in the process of migrating southward from their summer breeding grounds in Alaska. Half the birds were juveniles of about three months in age that had never migrated before, while the other half were adults that had made the round trip to their wintering site in the southwestern United States at least once.
After the birds were released, they attempted to resume their migration, but both age groups grew disoriented quickly.
"All the birds sc
|Contact: Chad Boutin|