Abstracts

Presented by Mason A. Hill - Email: mahill@ucdavis.edu

As the largest estuary on the Pacific Coast of North America, San Francisco Bay (SFB) is a critically important waterfowl stop-over and wintering area. Diving ducks account for up to 75% of the waterfowl observed during the midwinter survey in SFB and adjacent managed ponds. This region is characterized by cyclical drought, increasing urbanization, non-native species invasions, and intensive water management. Consequently, diving ducks using this system are subjected to frequent changes in the quantity and quality of available habitat and associated prey. Waterfowl body condition can be a useful metric for measuring the quality of wintering ground habitat that can be linked to reproductive success and survival. Thus, our objective was to assess seasonal and annual variations in body condition of the four most abundant diving duck species (Canvasback, Greater and Lesser Scaup, and Ruddy Duck) in SFB. During November through April of 2017 - 2018 and 2018 - 2019 we collected 307 diving ducks to assess body condition using proximate analysis of moisture, lipid, protein, and mineral content. Initial generalized linear mixed models suggest that moisture and lipid content of all four species fluctuates seasonally, with some of the lowest values occurring in March when individuals should be maximizing endogenous reserves for migration and breeding. As body condition can be among the most important determinants of breeding propensity in diving ducks, understanding the underlying factors driving these trends is critical for optimizing restoration and management that can benefit diving duck winter habitat in SFB.