Diving duck abundance and distribution on Lake St. Clair and western Lake Erie

Lake St. Clair and western Lake Erie are important migration staging areas for diving ducks including canvasbacks (Aythya valisineria), redheads (Aythya americana), and lesser and greater scaup (Aythya affinis and Aythya marila). The Michigan DNR has censused diving ducks on the United States portion of Lake St. Clair dating back to 1983, but in 2010 traditional surveys were expanded to cover all of Lake St. Clair and portions of western Lake Erie and distance sampling techniques were adopted in an effort generate statistical estimates of abundance. Furthermore, GPS locations were recorded for all flocks allowing for the development of spatial models to investigate the effects of environmental and anthropogenic variables on diving duck distribution. We found distance sampling techniques to be a viable option for estimating diving duck abundance as long as flock size is accounted for as a covariate affecting the detection function, and we were able to apply distance sampling methods to both spring and fall migration. Human disturbance (i.e., presence of boats) and environmental variables (i.e., water depth and plant species richness) were predictive of diving duck occurrence, although the importance of each variable was different depending on migration season (e.g., spring or fall). Differences between spring and fall abundance and variables predictive of spring and fall occurrence may indicate diving ducks are adopting different landscape use strategies in fall compared to spring, and this may have significant implications for wetland conservation planning.