Andrew DeWoody, at left, used DNA from eagle feathers to get more accurate counts of eagle populations that may be used for better conservation of the birds. Credit: Purdue Univ. |
Using genetic methods to count endangered eagles, a group
of scientists showed that traditional counting methods can lead to incorrect
totals that they believe could adversely affect conservation efforts.
Andrew DeWoody, a professor of genetics at Purdue Univ.;
Jamie Ivy, population manager at the San Diego Zoo; and Todd Katzner, a
research assistant professor at the Univ. of West Virginia, found that visual
counts of imperial and white-tailed sea eagles in the Narzum National Nature
Reserve of Kazakhstan underestimated the imperial eagle population there. Using
DNA from eagle feathers gathered in the area, the researchers were able to
identify individual DNA fingerprints for each bird.
The technique showed that there were 414 eagles, more than
three times as many as had been visually observed, and more than two and a half
times more than modeling suggested would be there.
“A biologist doesn’t always see them coming and
going,” said DeWoody, whose findings were published in the early online
version of the journal Animal
Conservation. “Eagles are difficult to capture, mark and resight.
Biologists in the field can’t differentiate individuals, whereas by a genetic
fingerprint geneticists can differentiate among individuals that have visited a
site.”
DeWoody, Ivy and Katzner, with collaborator Evgeny Bragin
of the Narzum Natural Nature Reserve collected thousands of eagle feathers
around roosts and nesting sites. DeWoody’s team at Purdue was able to extract
DNA from those feathers and determine that there were hundreds of eagles that
had recently visited the site.
“Generally we say ‘what you see is what you get,’ but
in this case it’s the complete opposite,” said Katzner, who used the data
to model more accurate estimates of eagle populations. “When your field
data are off by that much, it’s difficult to build accurate models because your
starting point is just so far off.”
DeWoody and Katzner said accurate animal counts are an
important part of conservation practices. If populations are underestimated, it
could signal to decision makers that a habitat isn’t important when, in
reality, more animals are using it than thought. Conversely, if a population is
more abundant than once thought, resources may need to be reallocated.
“We don’t want to spend a lot of effort protecting a
species that doesn’t need that much protection,” DeWoody said. “This
is a science-based approach to conservation.”
In the case of eagles in Kazakhstan, Katzner said the new
population estimates show that the Narzum National Nature Reserve is a more
important site than previously thought.
“We knew it was an important site for eagles, but we
seriously underestimated its importance,” Katzner said. “We used to
think this was only an important site for breeders, but now we know this is an
important site for birds from several life stages.”
The data will be used to begin discussions about managing
resources for eagles in Kazakhstan.
DeWoody hopes that the findings will increase funding to use the technique on
other threatened or endangered species. He said of particular interest to him
is the Steller’s sea eagle, a bird native to northeast Asia and thought to have
a population of only a few thousand.
