Autumn Migration of the Northern Saw-whet Owl on the Lower Delmarva Peninsula: Fall 2012 Report
The Northern Saw-whet Owl (Aegolius acadicus) breeds in southern Canada and the northern United States. During the late fall months this species migrates south to the mid-latitudes of North America. Because of its secretive habits, little was known about the Northern Saw-whet Owl’s migration ecology and winter distribution prior to the increase in the number of banding operations during the late 1990’s. During the fall of 1994, The Center for Conservation Biology began a study of migrant Northern Saw-whet Owls along the lower Delmarva Peninsula. This study has been the first to document large numbers of migrants south of Maryland. During the 19-year study, 3,850 owls have been banded and more than 100 foreign recaptures and returns have been recorded. We have also recorded more than 1000 same year recaptures. The owl migration project is conducted each year between the third week of October and the middle of December. Three trap sites (Eastern Shore of Virginia National Wildlife Refuge, Gatr Tract/Mockhorn Island Wildlife Management Area, and Kiptopeke State Park) consisting of 6 mist nets and a continuous-loop audio-lure are opened nightly from dusk to dawn. Among other objectives, the project seeks to 1) determine the annual variation in the magnitude and timing of Northern Saw-whet Owl migration through the lower Delmarva Peninsula, 2) determine the spatial pattern of habitat use near the tip of the Delmarva Peninsula, 3) determine the relative timing of passage for different age classes of Northern Saw-whet Owls, and 4) determine the rate of movement of Northern Saw-whet Owls moving down the Atlantic Flyway. During the fall of 2012, 315 new owls were captured and processed during 44 nights and 8,343 hours of operation. Capture rate was 7.2 owls/night or 3.8 owls/100 net-hours. Age ratio was 86.0% (271 birds) hatching-year (HY) birds compared to 14.0% (44 birds) after-hatching-year (AHY). Nine Eastern Screech Owls (Otus asio) were also captured during the season.