LARGE SCALE MIGRATION MOVEMENTS AND MIGRATORY PATTERNS IN EASTERN POPULATIONS OF THE NORTHERN SAW WHET OWL (Aegolius acadicus) – A REANALYSIS

Abstract

I analyzed banding and recapture data from the U.S. Geological Survey’s Bird Banding Laboratory (BBL) to reveal annual migratory trends in eastern populations of the Northern Saw-whet Owl (Aegolius acadicus) following the methodology framework described by Beckett & Proudfoot (2011). I analyzed 150,427 banding events and 6,208 recapture events during post-breeding migration (1 Sep to 31 Dec) between 2009-2022. I found significant regional differences in migratory route fidelity, with owls banded in the Great Lakes Basin exhibiting stronger fidelity to specific movement corridors compared to those in the Appalachian Mountains and Atlantic Seaboard regions. Age-differentiated migration patterns revealed a significant latitudinal difference between adults and juveniles, with juveniles generally banded at higher latitudes. However, this difference was small in magnitude and likely influenced by localized juvenile concentrations in northern Ontario and the western Great Lakes. Owls also demonstrated region-specific migratory directionality, with significantly different directional bearings among regions. The most concentrated southerly movements were found in Great Lakes owls, while birds of the Atlantic Seaboard had the most southwesterly direction, and those of the Appalachians an intermediate direction. These findings demonstrate that physiographic features, age structure, and wind exposure interact to influence migratory strategies in this species, reinforcing and clarifying earlier findings of Northern Saw-whet Owl migration ecology.