Status and trends in demography of northern spotted owls, 1985-2003.

Abstract

We analyzed demographic data from northern spotted owls(Strix occidentalis caurina)from 14 study areas in Washington, Oregon, and California for 1985-2003. The 14 study areas made up approximately 12 percent of the range of the subspecies and included federal, tribal, private, and mixed federal and private lands. Our primary objectives were to estimate fecundity, apparent survival, and annual rate of population change, and to determine if there were any temporal trends in these population parameters. The meta-analysis on fecundity indicated substantial annual variability with no increasing or decreasing trends. The meta-analysis of apparent survival indicated differences among regions and changes over time with a downward trend in the mixed-conifer and Douglas-fir regions of Washington. The meta-analysis of apparent survival also indicated that there was a negative association between fecundity and survival the following year, suggesting a cost of reproduction on survival. Data suggested that populations over all the areas were declining about 3.7 percent per year during the study. Results also suggested that owl populations on federal lands had higher demographic rates than elsewhere; thus, the Northwest Forest Plan appeared to have a positive effect on demography of northern spotted owls. Populations were doing poorest in Washington, where apparent survival rates and populations were declining in all study areas. The possible causes of population declines include habitat loss from timber harvest, competition from barred owls, fire, and weather patterns.

Citation

Anthony, R.G.; Forsman, E.D.; Franklin, A.B.; Anderson, D.R.; Burnham, K.P.; White, G.C.; Schwarz, C.J.; Nichols, J.D.; Hines, J.E.; Olson, G.S.; Ackers, S.H.; Andrews, L.S.; Biswell, B.L.; Carlson, P.C.; Diller, L.V.; Dugger, K.M.; Fehring, K.E.; Fleming, T.L.; Gerhardt, R.P.; Gremel, S.A.; Gutierrez, R.J.; Happe, P.J.; Herter, D.R.; Higley, J.M.; Horn, R.B.; Irwin, L.L.; Loschl, P.J.; Reid, J.A.; Sovern, S.G. 2006. Status and trends in demography of northern spotted owls, 1985-2003. Wildlife Monographs. 163(1): 1-48