Relation between Occupancy and Abundance for a Territorial Species, the California Spotted Owl

Land and resource managers often use detection–nondetection surveys to monitor the populations of species that may be affected by factors such as habitat alteration, climate change, and biological invasions. Relative to mark‐recapture studies, using detection–nondetection surveys is more cost‐effective, and recent advances in statistical analyses allow the incorporation of detection probability, covariates, and multiple seasons. We examined the efficacy of using detection–nondetection data (relative to mark‐recapture data) for monitoring population trends of a territorial species, the California Spotted Owl (Strix occidentalis occidentalis). We estimated and compared the finite annual rates of population change (λₜ) and the resulting realized population change (Δₜ) from both occupancy and mark‐recapture data collected over 18 years (1993–2010). We used multiseason, robust‐design occupancy models to estimate that territory occupancy declined during our study (Δₜ = 0.702, 95% CI 0.552–0.852) due to increasing territory extinction rates (ɛ̂1993 = 0.019 [SE 0.012]; ɛ̂2009 = 0.134 [SE 0.043]) and decreasing colonization rates (γ̂1993 = 0.323 [SE 0.124]; γ̂2009 = 0.242 [SE 0.058]). We used Pradel's temporal‐symmetry model for mark‐recapture data to estimate that the population trajectory closely matched the trends in territory occupancy (Δₜ = 0.725, 95% CI 0.445–1.004). Individual survival was constant during our study (ϕ̂1993 = 0.816 [SE 0.020]; ϕ̂2009 = 0.815 [SE 0.019]), whereas recruitment declined slightly (f̂1993 = 0.195 [SE 0.032]; f̂2009 = 0.160 [SE 0.023]). Thus, we concluded that detection–nondetection data can provide reliable inferences on population trends, especially when funds preclude more intensive mark‐recapture studies. Relación entre Ocupación y Abundancia en una Especie Territorial, el Búho Moteado de California