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New Mexico State University

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California spotted owls may need large reserves to sustain their populations

LAS CRUCES - Managing California spotted owls in a few fairly large conservation areas may be better than in many small areas, said a New Mexico State University wildlife scientist.

The California spotted owl, which is found from the mountains of northern California down the Sierra Nevada to the mountains of southern California, isn't as scarce as its cousin the Mexican spotted owl.

However, it is considered a sensitive species by the U.S. Forest Service, said Mark Andersen with NMSU's Agricultural Experiment Station. That means a management plan is required to sustain the owl's population under the National Forest Management Act.

Andersen and Dipak Mahato of North Carolina State University used demographic models to compare two spotted owl conservation strategies. In one strategy -- the spotted owl habitat area strategy -- a large number of small reserves with one to three nesting sites are used. In the other strategy -- the habitat conservation area plan -- a smaller number of larger reserves with 10 to 20 active nests are used.

"We found that the larger reserves are much more effective at maintaining the owl populations into the future," Andersen said.

Andersen said this seems to be a result of the behavior of juvenile spotted owls when they are searching for suitable places to live after leaving their nests. The owls are more likely to find good places to nest within larger reserves that have a greater variety of trees of different ages than in smaller reserves, he said.

"From our study, the basic recommendation is that the Forest Service should set aside fairly large areas for conservation of the California spotted owl," Andersen said.

"That might not require prohibiting logging, but it may require prohibiting clear cutting. This could be difficult for the Forest Service to come to grips with, because the policy in California has been to promote clear cut rather than selective harvest."

One factor the researchers considered in their models that Andersen said is sometimes overlooked is the effect of forest fires on owl populations. "Fire isn't much of a problem in the Northwest where the Northern spotted owl lives, but it is a fairly important problem in the drier climate of California."

Results of this study were recently published in the journal Ecological Applications.