Code

CCBTR-11-19

Publication Date

2011

Abstract

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 17-year study, 3,535 owls have been banded and more than 100 foreign recaptures and returns have been recorded. We have also recorded more than 500 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 2011, 40 new owls were captured and processed during 40 nights and 7,415 hours of operation. Capture rate was 1.0 owls/night or .54 owls/100 net-hours. Age ratio was 62.5% (25 birds) hatching-year (HY) birds compared to 37.5% (15 birds) after-hatching-year (AHY). In addition to the Northern Saw-whet Owls captured during the season, 4 Eastern Screech Owls (Otus asio) were captured.

Species

Northern Saw-whet Owl

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