Population ecology of the spotted owl in the central Sierra Nevada, California

Author

Daryl W. Lutz

Graduation Date

1992

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Wildlife Management, 1992

Committee Chair Name

R.J. Gutierrez

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Owls, Bird populations, Spotted owl, Sierra Nevada, Humboldt State University -- Theses -- Wildlife Management

Abstract

I studied the demography of California spotted owls(Strix occidentalis occidentalis) in the central Sierra Nevada, California between 1986 and 1989. Fifty-five spotted owls were banded during the study. Estimates of fecundity, nest success, and productivity were 0.34, 42.0%, and 1.70, respectively. Of thirty-nine territories monitored, on average 55% and 21% were occupied by pairs or single owls, respectively, while 24% were unoccupied. Population size was estimated empirically, from Jolly-Seber models A and D, and from Leslie regression analysis. The population estimates were 36, 33, 32, and 40 birds, respectively. All estimates were statistically the same. Goodness of fit tests indicated that the data from this study satisfied the assumptions of the Jolly-Seber models. Crude density was 0.09 owls/km2 and was significantly less than that reported for the northern spotted owl. Standard Lotka-Leslie models were used to assess the sensitivity of A to variation in the vital rates and to project population trends. Parameters estimated were adult survival rate (S) = 0.76, juvenile survival rate (S0) = 0.16, and fecundity = 0.34. The empirical estimate for adult survival was not significantly different from the Jolly-Seber model A estimate. The population's finite rate of growth, λ, was most sensitive to adult survival rate and age of senescence. Fecundity, subadult, and juvenile survival rate did not dramatically influence estimates of A. The value of A for this population was 0.811, which was significantly less than 1.0. At this rate of decline the population's half life is 4 years.

https://scholarworks.calstate.edu/concern/theses/pg15bh27p

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