A PASSIVE ACOUSTIC FRAMEWORK FOR MONITORING RAPIDLY EXPANDING BARRED OWL POPULATIONS
|Whitney A Watson; University of Wisconsin - Madison; email@example.com; Connor M. Wood, Kevin G. Kelly, Daniel F. Hofstadter, Nicholas F. Kryshak, Ceeanna J. Zulla, Sheila A. Whitmore, Virginia O'Rourke, John J. Keane, M. Zachariah Peery
Barred Owls (Strix varia) have recently expanded westward from eastern North America, leading to substantial declines in Northern Spotted Owls (Strix occidentalis caurina). Passive acoustic monitoring (PAM) represents a potentially powerful tool for tracking range expansions like the Barred Owl’s, but further methods development is needed to ensure that PAM-informed occupancy models meaningfully reflect population processes. We used a combination of PAM data, GPS-tagging, and active surveys to identify patterns of vocal activity that best reflect resident occupancy and subsequently estimated resident occupancy rates by correcting site occupancy estimates using vocal activity thresholds. The proportion of survey nights with confirmed vocalizations (VN) and the number of ARUs within a sampling cell with confirmed vocalizations (VU) were strongly indicative of Barred Owl residency. Applying thresholds of VN > 0.17 and VU = 3 to our occupancy analysis, we were able to minimize false positive and negative errors, and we estimated the occupancy rate for resident owls to be 0.45. Our findings provide a scalable framework for monitoring Barred Owl populations throughout their expanded range and, more broadly, a basis for converting site occupancy to resident occupancy in PAM programs—thus ensuring changes in occupancy rates reflect changes in populations.