The Dulling Effect of Sex

For the colorful American redstart, breeding late into the season can leave some males looking rather dull, a new study shows.

When redstart males are busy catching insects for their young late into the breeding season, they don't have time or energy to replace their feathers before the long migration from their summer homes in North America to their winter homes in Central America.

This means they have to stop during the trip south to grow new feathers. The birds don't grow feathers during flight. They need to stop for at least a week. Bird researcher Ryan Norris from Queens University in Kingston, Canada says a redstart can grow a tail feather in a week or two. Most birds need to grow a new set of feathers at least once a year in order to keep flying.

Norris his colleagues studied the same group of American redstarts for several summers in Ontario, Canada. The dads that were busy parenting late in the summer often replaced their feathers during migration. These males grew duller tail feathers than the males that had time to grow new feathers before migration. Having dull tail feathers makes it more difficult for male redstarts to attract a mate the next spring, the scientists found.

The study is detailed in the Dec. 24 issue of the journal Science.

Norris was excited to find that some birds stop during their long flight south to grow new feathers. This discovery suggests that these birds use rest areas along the migratory flyway that should be protected. The new research also provides insights into connections between breeding, migrating and feather replacement for American redstarts and probably other kinds of songbirds.

-- LiveScience Staff

Image credit: © Science/ Illustration by John P. O'Neill