J.R. Goldsberry D.G. McAuley E.L. Derleth G.M. Haramis 1985 <p>We used conventional 35-mm photography to conduct an aerial photographic census of canvasbacks (<i>Aythya valisineria</i>) throughout Chesapeake Bay (tidal Maryland and Virginia) and coastal North Carolina, 26-30 January 1981. Flock size and sex ratio characteristics were determined from examination of color transparencies of 165 canvasback flocks totaling over 95,000 birds. A sex ratio of 2.91 males/female was determined from 68,769 birds, 80% of the birds in 150 flocks. Sex ratio for the Atlantic Flyway was projected as 2.90 males/female. We recorded the greatest number of canvasbacks and the widest range of flock size in Maryland waters; the fewest canvasbacks and the smallest average flock size in Virginia; and the fewest but on average the largest flocks of canvasbacks in North Carolina. Sex ratio varied latitudinally in the flyway with a tendency for males to occupy more northern and females more southern latitudes in winter. Sex ratio (males/female) was highest in Maryland (3.98), slightly lower in Virginia (3.71), and lowest in North Carolina (1.70). Locally, sex ratio varied with flock size. In Chesapeake Bay, small flocks (&lt;100 birds) had lower sex ratio (P &lt; 0.05) than medium (100-1,000) or large (&gt;1,000) flocks. By providing large- sample sex ratio information, as well as exact counts of birds, we conclude that low-level 35-mm aerial photography is the most efficient and accurate means of determining canvasback population status in eastern coastal habitats.</p> application/pdf 10.2307/3801550 en Wiley An aerial photographic census of Chesapeake Bay and North Carolina canvasbacks article