Factors that influence body condition of waterfowl during winter may greatly impact waterfowl populations. Winter survival, propensity to nest, and nest success are all affected by body condition of individual birds, which depends on food density and abundance. Thus, habitat programs that improve the body condition of wintering waterfowl may increase waterfowl populations by improving both survival and recruitment. Ideally, winter habitat provides food to ensure that ducks leave wintering grounds in condition adequate to support nutritional needs during spring migration and nesting.
Wintering waterfowl habitat area and distribution have changed since the Central Valley Joint Venture (CVJV) started work in 1986 to improve habitat conditions in the Central Valley. Conservation programs such as the CVJV have increased and enhanced wetland and agricultural habitats throughout the Central Valley. Changing agricultural practices have also impacted waterfowl habitats, with increased rice acreages and mandated phase-out of rice straw burning (Assembly Bill 1378), resulting in a 46% increase in the area of winter-flooded rice between 1988 and 1999, mainly in the Sacramento Valley. The North American Waterfowl Management Plan has directed its Joint Ventures to develop biological measures of success. However, to date, most have simply tracked numbers of acres provided and dollars expended in wetland restoration and conservation.
In a project led by graduate student Doug Thomas, we studied the body condition of waterfowl to determine how nutritional status of birds has responded over time to habitat improvements, in order to fulfill the North American Waterfowl Management Plan directive and help guide its conservation programs. We are consolidating existing data for meta-analysis and collecting new key comparative data to provide the CVJV with an understanding of factors impacting waterfowl body condition and as a measure of the population response to their habitat management and conservation efforts. We are collecting new data from hunter check stations and targeted field collections. Hunter check stations provide an opportunity to obtain a large number of samples from a wide variety of species and geographic locations. However, because hunter-shot birds may be in poorer condition than the general population and samples are only available during hunting season, we are also collecting samples of selected species in targeted locations. This study will provide a test of the assumption that wintering waterfowl food resources were previously limited and will enable a measure of the biological effectiveness of on-going habitat programs.