Data and Model-Based Estimates from Black Brant (Branta bernicla nigricans) Fall Age Ratio Surveys at Izembek Lagoon, Alaska

Surveys were generally conducted from elevated shoreline locations that provided unobstructed views of geese as they fed on eelgrass close to shore or at consistent roosting and gritting locations. Since 1995,observers occasionally use boats to access and survey brant flocks at offshore eelgrass meadows that were under-represented in the early years (1960s to 1980s) of the age ratio surveys. We selected locations for observations that maximized visibility of geese and accounted for vantage point and weather conditions, such as precipitation, sun glare, and especially wind strength and direction, which are dominating forces in this region. We aged geese while viewing a flock through spotting scopes (10–120×) and tallying adult and juveniles on a hand counter. We distinguished juvenile brant from adults by the presence of white edging on the distal ends of secondary wing coverts. We typically started scans at one end of the flock and moved through the flock from closest to the distant edge, usually until we aged ≥30% of the flock. We took care not to age birds only at the edge of flock, where juveniles tend to concentrate. During a flock survey, observers recorded the location, date, time of observation, tide stage (flood, ebb, low, high), number of adults and juveniles aged, and approximate total flock size (Ward et al. 2018).