Photo by Tom Campbell Andrew DeWoody (left) and Jamie Rudnick conduct DNA research on feathers eagles leave in the nest.

A trail of feathers led a team of Purdue University scientists to confirm that eagles from centra Asia are possibly the most faithful of birds.

By performing DNA analysis on the feathers, researchers were able to identify individual Eastern imperial eagles in a nature reserve in Kazakhstan. Their analysis showed that not one adult strayed from its mate - a degree of fidelity highly unusual among birds, the vast majority of which mate with and raise offspring from multiple partners.

"That we were able to use feathers we collected noninvasively as a source of DNA is the number one thing scientists will be interested in," said Andrew DeWoody, associate professor of genetics and senior author of the study.

"People have been doing studies like this for years with mammals, but this is a first for birds."

By developing a protocol for extracting DNA from feathers, the researchers have added another tool to help conservation biologists study rare and elusive birds of prey.

The researchers used a technique called DNA fingerprinting to help them genetically "tag" individuals in the population without capture, said Jamie Rudnick, the graduate student who conducted the study as part of her doctoral thesis.

"Collecting feathers in the nest helped determine population parameters we wouldn't have been able to otherwise," she said.

Those parameters, such as yearly survival rates and ratios of males to females, help conservation biologists monitor populations of rare or endangered species. Noninvasive sampling allows biologists to track changes in populations over time without the risks associated with handling live animals.

"Eastern imperial eagles are hard to catch, and individuals are difficult to tell apart," Rudnick said. "By performing genetic analysis on feathers collected at the site, we were able to track the presence or absence of individual birds over a six-year period."

Observational studies of imperial eagles suggest these birds, like most large birds of prey, are at least socially monogamous. This means a male-female pair stays together throughout the breeding season and shares responsibility in raising young, DeWoody said.

But just because two individuals act like a pair doesn't guarantee they're not having trysts. In fact, studies over the last decade have shown most broods of socially monogamous birds include offspring from at least two genetic fathers.

"Our study actually stands out as a relatively rare instance in which DNA fingerprinting uncovers genetic monogamy in a bird population," DeWoody said.

Contact DeWoody at: dewoody@purdue.edu