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Updated 12:30 PM February 14, 2007




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Peregrines on probation: Population's prospects appear promising

The recently endangered peregrine falcon of North America got a health checkup of sorts and the prognosis looks good. A team of population geneticists, including a U-M graduate student, got an unexpected result when they measured levels of DNA variation in the current cohort of falcons.
(Photo by Gordon Court)

Using the DNA of museum specimens collected between 1885 and 1951 for comparison, the researchers found that the genetic variability of today's falcons was similar, and in some cases higher, than it was historically, a positive indicator for the future of the species in Canada.

The results of their study appear in the January issue of the journal Molecular Ecology.

In the mid-1900s, peregrine falcon populations were wiped out east of the Great Plains and were devastated in other parts of North America, primarily due to the introduction of pesticides containing DDT. Expansive breeding and reintroduction programs, and pesticide use controls in the United States and Canada, aided in the return of many populations to original size.

When a species is decimated in a particular region, as the peregrine falcon was, and then makes a comeback, scientists call this a bottleneck. Typically, bottlenecks result in reduced genetic variability. This reduced variability increases the risk of extinction.

When graduate student Joseph Brown and his colleagues examined peregrine falcon DNA they anticipated finding very low DNA variation because today's peregrines were reintroduced into the wild from a very small population of approximately 100 pairs of falcons. Throughout the 1970s -1980s, 7,000 chicks were released as part of extensive breeding programs in the U.S. and Canada.

"The elevated diversity that we found came as a big surprise," says Brown, a doctoral student in ecology and evolutionary biology who is affiliated with the Bird Division of the U-M Museum of Zoology.

He and his coworkers wondered how such high diversity could be found in a population that had been so small at one time. They came up with two answers. First, if the response to a bottleneck is very quick, much of the variation may be preserved. In the case of peregrine falcons, the birds bottomed out in the early 1970s—around the same time the expansive breeding programs began in the U.S. and Canada.

The second explanation for higher than anticipated diversity involves the introduction of genes from birds outside North America. Whereas Canadian efforts focused on conserving one subspecies, the American Peregrine Falcon, Falco peregrinus anatum, the U.S. program bred a minimum of seven subspecies from around the world including those from Spain, Scotland and South America. The likely event that any of these birds flew across the border to Canada to breed could account for elevated genetic diversity.

There were two main questions: How much genetic variation had the falcons lost as a result of their dramatic decline and reintroduction? And what were the genetic consequences of the DDT-induced bottleneck of the mid-20th century?

Without the historical data from the Royal Ontario Museum and the Canadian Museum of Nature for comparison, the researchers likely would have reached the wrong conclusion, Brown says.

"If we had just looked at the contemporary birds, we would have come to different conclusions. We'd have thought 'that's pretty low diversity; they're not doing so great.' By looking at DNA samples from the museum specimens, we can see there's always been low diversity," Brown says.

Even more surprisingly, he found that among the Arctic and American Peregrine Falcons, the variation was even higher than the historical data showed.

The Molecular Ecology paper currently is being used by the Canadian governmental groups the Committee on the Status of Endangered Wildlife in Canada and Sara Species at Risk Act, to decide whether peregrines can be removed from their probationary period. Currently, every five years peregrines are being tracked to their remote cliffside homes across Canada, an expensive and labor-intensive process.

"In terms of levels of DNA variation, the peregrine falcon looks healthy and should be able to cope with whatever environmental stresses it might have to face," Brown says. "All signs point to them being pulled off probation."

In fact, the world's fastest flying birds are being seen performing their record-breaking swoops and dives in places they've never been seen before, like the pair in and around the Bell Tower on campus.

Co-authors include Peter Van Coeverden de Groot, Tim Birt, Peter Boag, and Vicki Friesen of Queen's University in Ontario, Canada; and Gilles Seutin, who manages the endangered species program at the Parks Canada Agency. Parks Canada and the Natural Sciences and Engineering Research Council of Canada provided funding.

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