Study: Shrinking gene pool among spotted owls contributing to their decline

Article Date: 2009-06-10   Source: http://www.oregonlive.com   Comments: 0

By Matthew Preusch

Oregon, U.S.A. - When the northern spotted owl went on the endangered species list in 1990, it effectively brought federal lands logging to a halt in the Northwest.

Nearly two decades later, the number of owls is still dropping, and their shrinking gene pool is part of the problem, a new study concludes.

Fewer birds make for a genetic "bottleneck" that increases the potential for interbreeding and reducing the birds' ability to adapt, says the study published this month in the journal Conservation Genetics.

"Our results provide independent evidence that northern spotted owls have recently declined, and suggest that loss of genetic variation is an emerging threat to the subspecies' persistence," said the reports' authors, including U.S. Forest Service biologist and longtime owl expert Eric Forsman .

Despite the increase in federal forests set aside for the owl under the 1994 Northwest Forest Plan, their numbers continue to decline at a rate of about 3.7 percent per year, the study found.

That's in part due to continued loss of habitat as well as competition from the non-native barred owl, which is larger than the spotted owl and has moved into its territory. The decline is most dramatic in Washington State.

But this new study, which surveyed 352 spotted owls, suggests that the relatively small population of birds may itself be a limiting factor to their recovery.

"Reduced effective population size shown here in addition to field evidence for demographic decline highlights the increasing vulnerability of this bird to extinction," the study says.

Related Articles:
2009-12-09 - Barred owls could get the boot (or a bullet) to save spotted owls by Matthew Preusch - Portland, Oregon, U.S.A.
2008-05-17 - Plan for saving spotted owl recommends maintaining older forests west of the Cascades by Michael Milstein - Oregon, U.S.A.
2007-07-29 - So much for saving the spotted owl by Michael Milstein - Oregon, U.S.A.
2007-06-15 - Critical habitat proposal draws different lines on Forest Service and BLM land by Adam Pearson - Oregon, U.S.A.
2007-05-06 - A spotted owl fix by Susan Palmer - Oregon, U.S.A.
2005-02-13 - Rare owl has birders flocking to Bend by Matthew Preusch - Bend, Oregon, U.S.A.
2004-07-22 - Owls Face Spotted Future by Sharon Guynup & Nicolas Ruggia - Oregon, U.S.A.
2004-05-31 - A no-holds-barred owl war by Michael Milstein - Oregon, U.S.A.

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