Title: Northwest Forest Plan—the first 10 years (1994–2003): status and trends of northern spotted owl populations and habitat.
Author: Lint, Joseph tech. coord.;
Source: Gen. Tech. Rep. PNW-GTR-648. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 176 p
Publication Series: General Technical Report (GTR)
Description: This report presents results from monitoring spotted owl (Strix occidentalis caurina) populations and habitat during the first 10 years of implementation of the Northwest Forest Plan (the Plan). Estimated population decline ranged from 0 to 10 percent across study areas (weighted average of 3.4 percent) annually. The average annual rate of decline for the four demographic areas in Washington was 7.1 percent. Presence of barred owls (Strix varia), weather, past and present harvest of habitat, and wildfire and insect infestations that alter habitat are all possible contributors to the noted decline.
Maps depicting the suitability of habitat-capable area were produced by using habitat models. Rangewide (range of the owl), about 74 percent of the federal land area was habitat-capable. Fifty-seven percent of the habitat-capable area was in a forest condition similar to the conditions where territorial owls were known to be present on the landscape. Fifty-one percent of the habitat-capable area fell in large, reserved blocks intended, under the Plan, to support clusters of reproducing owls. About 62 percent of the habitat-capable area inside the reserved blocks was in a forest condition similar to the conditions where owls were known to be present.
Owl movement was assessed in selected provinces by using data from banded owls. Movements with resighting locations inside reserved blocks accounted for 51 percent of juvenile movement records. Over 30 percent of the juvenile movements were into reserved blocks from outside points.
Predictive model development using demographic data showed a variety of factors that influence owl survival and productivity including precipitation, owl age, and habitat.
The barred owl has expanded its range in past decades and currently is present throughout the range of the spotted owl. The likelihood of competitive interaction between spotted owls and barred owls raises concern on the future of spotted owl populations. Barred owls are high on the list of factors that may be contributing to spotted owl declines in northern portions of the spotted owl’s range.
Barred owls, West Nile virus(Flavivirus sp.), and management of owl habitat in high-fire-risk areas are topics for future management consideration.
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Lint, Joseph, tech. coord. 2005. Northwest Forest Plan—the first 10 years (1994–2003): status and trends of northern spotted owl populations and habitat. Gen. Tech. Rep. PNW-GTR-648. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 176 p
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