Abstract

Owls occur at relatively low densities and are cryptic; thus, monitoring programs that estimate variation in detectability will improve inferences about their presence. We investigated temporal and abiotic sources of variation associated with detection probabilities of rufous-legged owls (Strix rufipes), a threatened forest specialist, and austral pygmy-owls (Glaucidium nana), a habitat generalist, in temperate forests of southern Chile. We also assessed whether detection of 1 species was related to the detection of the other species. During 2011-2013, we conducted 1,145 broadcast surveys at 101 sampling units established along an elevational gradient located inside and outside protected areas. We used a multi-season occupancy framework for modeling occupancy () and detection (p), and ranked models using an information-theoretic approach. We recorded 292 detections of rufous-legged owls and 334 detections of austral pygmy-owls. Occupancy was positively associated with elevation for rufous-legged owls but constant (i.e., did not vary with covariates) for pygmy-owls. Detectability for both owls increased with greater moonlight and decreased with environmental noise, and for pygmy-owls greater wind speed decreased detectability. The probability of detecting pygmy-owls increased nonlinearly with number of days since the start of surveys and peaked during the latest surveys of the season (23 Jan-7 Feb). Detection of both species was positively correlated with the detection of the other species. We suggest both species should be surveyed simultaneously for a minimum of 3-4 times during a season, survey stations should be located away from noise, and observers should record the moon phase and weather conditions for each survey. (c) 2014 The Wildlife Society.