And it's all about the feathers.
Researchers were surprised to discover that the timing of a male songbird's reproduction cycle affects the colour of his feathers and may have important implications for his success in attracting mates. When migratory songbirds raise their young extremely late in the summer, many don't have time to molt (shed their feathers and replace with new growth) before heading south, the new study shows.
"This means they must molt at stopover sites on their journey to tropical winter habitats," explains Ryan Norris, who conducted the research as part of his PhD in biology at Queen's, supervised by Professors Laurene Ratcliffe (Queen's Biology) and Peter Marra (Smithsonian Environmental Research Center).
"Their replacement feathers, grown en route, are less colourful than those of birds that had time to molt before migration, which may put them at a disadvantage in attracting females the following breeding season," says Dr. Norris. "Both findings that molting in some songbirds occurs after migration has begun, and that their new feathers are duller in colour were surprising."
The study will be published Dec. 24 in the journal Science.
Until now scientists have assumed that most species of migratory birds molt before they migrate. The team discovered that in fact some begin their migration, molt at a "stopover" site, then continue to their winter habitat. Forty per cent of the male American Redstarts in the study molted in their tail feathers at areas up to 2000 kilometers south of their breeding grounds.
By measuring stable hydrogen isotopes in the newly grown feathers when birds returned the following spring to breed at the Queen's University Biology Station north of Kingston,
Contact: Nancy Dorrance