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Demography of the California spotted owl in the Sierra National Forest and Sequoia/Kings Canyon National Parks

Author(s):

George N. Steger
Kenneth D. Johnson
Gary P. Eberlein

Year:

2002

Publication type:

General Technical Report (GTR)

Primary Station(s):

Pacific Southwest Research Station

Source:

In: Verner, Jared, tech. editor. Proceedings of a Symposium on the Kings River Sustainable Forest Ecosystem Project: Progress and Current Status. Gen. Tech. Rep. PSW-GTR-183, Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 107-116

Description

Nine years (1990–1998) of demographic data on California spotted owls (Strix occidentalis occidentalis) in two study areas on the western slopes of the Sierra Nevada—one in the Sierra National Forest (SNF), the other in Sequoia/Kings Canyon National Parks (SNP)—are summarized. Numbers of territorial owls fluctuated from 85 to 50 in SNF and 80 to 58 in SNP over the period from 1990 to 1998, and demographic parameters indicate significantly declining populations in both study areas during the same period. Owl densities in conifer forests, reproductive performance, and survival rates did not differ significantly between the two study areas. These results suggest that factors influencing population trends may be more than local in scope, such as weather and/or prey populations. Local forest management may compound the regional variation, however, as may be reflected in the lower adult/ subadult survival rates in the SNF study area compared to the SNP study area. Continual timber harvest has occurred in SNF since the late 1800's, but SNP has had little harvesting activity. Prescription burning and recreation continue to occur on both sites. Declining trends in owl numbers also reflect poor breeding success from 1995 through 1998, apparently attributable to unseasonal storms during the breeding period, especially during the incubation and nestling phases. Results suggest the hypothesis that spotted owls are "pulse" breeders that exhibit unusually successful reproduction only at intervals of several years, when all conditions are favorable. Continuation of these studies as part of the Kings River Sustainable Forest Ecosystems Project within boundaries of SNF will provide opportunities to explore relations among spotted owl demographics and timber harvest, weather, and prey availability.

Citation

Steger, George N.; Munton, Thomas E.; Johnson, Kenneth D.; Eberlein, Gary P. 2002. Demography of the California spotted owl in the Sierra National Forest and Sequoia/Kings Canyon National Parks. In: Verner, Jared, tech. editor. Proceedings of a Symposium on the Kings River Sustainable Forest Ecosystem Project: Progress and Current Status. Gen. Tech. Rep. PSW-GTR-183, Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 107-116

Publication Notes

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  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
https://www.fs.usda.gov/treesearch/pubs/26100