Using Search Time and Regression to Estimate Abundance of Territorial Spotted Owls

Using conventional sampling methods, unbiased, precise estimates of the number of individuals in a population can be difficult to obtain for rare, secretive species. We used a Leslie regression model (ARM) to estimate the number (N0) and the variance of the number (V[N0]) of adult and subadult Northern Spotted Owls in a territorial population from direct counts within a 292 km2 study area. Estimates of N0 from day counts were more accurate and precise and more robust to fluctuations in survey effort than estimates from night counts. ARM estimates from day counts were not significantly different from two different maximum—likelihood estimates and required 30—64% less effort. These findings suggest a less costly method for statistically comparing Spotted Owl abundance between spatial or temporal units.