SEAFWA 2018

AUTHORS: Pamela Garrettson, Guthrie Zimmerman – U.S. Fish and Wildlife Service

ABSTRACT: We report on work that combined data from the Atlantic Flyway Breeding Waterfowl Survey (AFBWS) and the North American Breeding Bird Survey (BBS) to estimate the number of wood ducks in the United States portion of the Atlantic Flyway from 1993 to 2013. The AFBWS is a plot-based survey covering most of the northern and central portions of the Flyway; when analyzed with adjustments for survey time of day effects, these data can be used to estimate population size. The BBS provides indices of wood duck abundance. Although factors influencing change in BBS counts over time can be controlled in BBS analysis, BBS indices alone cannot be used to derive population size estimates. We used AFBWS data to scale BBS indices for Bird Conservation Regions (BCR), basing the scaling factors on the ratio of estimated AFBWS population sizes to regional BBS indices for portions of BCRs common to both surveys. We summed scaled BBS results for portions of the Flyway not covered by the AFBWS with AFBWS population estimates to estimate a mean yearly total of 1,295,875 (mean 95% CI: 1,013,940–1,727,922) wood ducks. Scaling factors varied among BCRs from 16.7 to 148.0 (mean = 68.9, 95% CI: 53.5–90.9). Flyway-wide, population estimates from the combined analysis were consistent with alternative estimates derived from harvest data. We discuss the assumptions, advantages and drawbacks associated with this method, and possible extensions of this technique to other portions of wood duck range.