Spatially explicit population trend estimates of owls in the Maritime provinces of Canada and the influence of call playback

Documenting and interpreting trends in the abundance and distribution of bird populations is critical to monitoring their status and setting conservation priorities. This process requires standardized monitoring and robust analytical techniques, which can resolve trends at spatial scales of management interest while disentangling the influence that various data collection protocols can have on the interpretation of results. We used a 19-year citizen-science-collected dataset (2001-2019), the Nocturnal Owl Survey, to assess abundance trends in Barred Owl (Strix varia), Northern Saw-whet Owl (Aegolius acadicus), and Great Horned Owl (Bubo virginianus) at both fine and broad-scales. To achieve this, we used a spatially explicit modeling approach that facilitates the borrowing of information across spatial boundaries, allowing for more robust trend estimates at finer spatial scales. Further, we assessed the potential influence of the call-playback protocol on trend estimates. At fine spatial scales, we found that a data collection protocol that includes call playbacks provided more precise results to assess relative changes in abundance (i.e., reduced uncertainty). At broader spatial scales, trend estimates were unaffected by data collection methodology (i.e., silent listening versus call playback). Specifically, at the scale of the region or province, we found that populations of focal owl species in the Maritimes of Canada have remained stable over the past 19 years. However, at finer scales, trends are more variable and may create opportunities to test alternative hypotheses about drivers of population change and the effects of management actions at scales amenable to conservation action. The statistical analyses are anticipated to form a national, publicly accessible framework for status assessments of owls in Canada and will provide resource managers and researchers a base from which to evaluate the influence of land management and conservation practices on owl populations across the nation.