Winter Surveys for Mexican Spotted Owls with Audio Recorders

Monitoring Mexican Spotted Owls (Strix occidentalis lucida) in and near breeding territories during winter has practical value but has not been previously studied by passive techniques, including acoustic recorders. Such information could inform breeding survey strategies as well as identify new breeding pairs. The U.S. Fish and Wildlife Service’s standard survey protocol, entailing four nighttime visits to a site and listening for a response to broadcast calls, has limitations in winter, when nonbreeding owls are less likely to respond and multiple visits may not be possible. Instead, I tested the feasibility of using passive sound-recording equipment to detect the owl in winter, deploying audio recorders at two known nesting sites in northern Arizona over 6 months through winter 2014–2015. As a result, I recorded spontaneous calls during each month of the survey. Paired males and females called to each other in winter, and the variation in frequency of calling through the night paralleled the pattern found in previous studies. My data suggest that automated audio detection provides a reliable tool for continuous, high-resolution, long-term, and cost-effective monitoring of the Mexican Spotted Owl, in both winter and summer.