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An update of demographic estimates for the Northern Spotted Owls (Strix occidentalis caurina) from Oregon's Central Coast RangesAuthor(s): James A. Thrailkill; Robert G. Anthony; E. Charles Meslow
Source: In: Duncan, James R.; Johnson, David H.; Nicholls, Thomas H., eds. Biology and conservation of owls of the Northern Hemisphere: 2nd International symposium. Gen. Tech. Rep. NC-190. St. Paul, MN: U.S. Dept. of Agriculture, Forest Service, North Central Forest Experiment Station. 432-448.
Publication Series: General Technical Report (GTR)
Station: North Central Research Station
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DescriptionDemographic characteristics of the Northern Spotted Owl (Strix occidentalis caurina) were studied on the Eugene District Bureau of Land Management, central Oregon Coast Ranges from 1989-1995. Survival rates were estimated from capture histories of banded owls using Cormack-Jolly-Seber open population models. We banded 233 owls, including 119 that were ≥ 3 years old, 15 that were 1 or 2 years old, and 99 juveniles. Among year variation in the proportion of pairs nesting and fecundity of females was significant ( P < 0.001). Estimates of apparent annual survival from the selected capture-recapture models were 0.306 (SE = 0.064) for juveniles and 0.875 (SE = 0.018) for subadult and adult owls combined. The estimated annual rate of population change (0.939, SE = 0.045) was < 1.00 (P = 0.005) over the 6 years of study, suggesting an average population decline of 6.1 per cent per year. Counts of territorial owls decreased by 37 percent from 1990-1995 on the Wolf Creek density study area, a smaller area within the larger surrounding study area. We suggest the owl population decline was due to the reduction of spotted owl habitat.
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CitationThrailkill, James A.; Anthony, Robert G.; Meslow, E. Charles. 1997. An update of demographic estimates for the Northern Spotted Owls (Strix occidentalis caurina) from Oregon''s Central Coast Ranges. In: Duncan, James R.; Johnson, David H.; Nicholls, Thomas H., eds. Biology and conservation of owls of the Northern Hemisphere: 2nd International symposium. Gen. Tech. Rep. NC-190. St. Paul, MN: U.S. Dept. of Agriculture, Forest Service, North Central Forest Experiment Station. 432-448.
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