NUTRITIONAL, PHYSIOLOGICAL, AND BEHAVIORAL
RESEARCH ON CAPTIVE SEADUCKS
Changes in the distribution and abundance of some local populations of seaducks in Chesapeake Bay have been recorded and is of concern to waterfowl managers in the Bay area. The Bay also has undergone an extensive change in the food resources it offers wintering waterfowl due to the degradation of water quality. There is a need for research on the availability and nutritional quality of these food resources – particularly in areas of the Chesapeake Bay at depths of 20-40 feet where seaducks typically feed – as a possible explanation for the decline in the wintering populations. These areas may be the first to be impacted by anoxic conditions if poor water conditions occur during the summer months.
The Sea Duck Joint Venture (SDJV), established as a cooperative activity between the USFWS, the CWS, and state and provincial agencies, has recommended new research on captive seaducks at USGS Patuxent Wildlife Research Center (PWRC) to learn more about the problems that might be affecting their population status in the wild.
The overall goal of this study is to restore declining seaduck populations on wintering areas by providing data that will assist in future population monitoring and managing. Initial focus will be on the three species of scoters (black, surf, and white-winged) and the long-tailed duck. This proposed study has multiple objectives and are as follows:
• Compare food available at various depths in the Chesapeake Bay with known food habits of seaducks.
• Determine the influence of nutrients on condition, behavior, and blood chemistry of captive seaducks in winter.
• Analyze the influence of depth of water, density of food, and depth of substrate on feeding performance of seaducks (in dive tanks).
During 2003, a captive colony of seaducks will be established at PWRC. Eggs will be collected from the wild in northern Canada from nests of scoters (black, surf, and white-winged) and long-tailed ducks in areas where these species are successfully breeding. All incubation and propagation of the study will be conducted at PWRC.
Principal food organisms used by wintering seaducks in the Chesapeake Bay will be collected from major feeding areas. Proximate analyses of food sources for each species will determine experimental diets, which will vary by levels of energy and protein. Blood samples will be drawn from equal numbers of males, females, immatures, and adults from each of the treatment diets throughout the study to determine the effect of diet on blood parameters. Observers outside of pens will record the location and behavior of experimental ducks using scan sampling techniques.
Two large aquariums (dive tanks) were constructed and installed (2 x 3 x 3m) in a pen facility for use on feeding trials at PWRC. Food habits of the ducks and feeding habitats in the Chesapeake Bay have been evaluated to aid in the formulation of diets. Feeding performance of diving ducks will be tested to determine the influences of environmental factors such as depth of water, type of water (salt or fresh), density of food, and depth of substrate covering the food (Carbone 1995). To measure how a shift between food sources influences foraging energetics, we will evaluate each food type in terms of profitability (energy intake – cost of diving), measuring both (1) the assimilation frequency (fraction of ingested energy absorbed by the gut) of different food sources found in the Chesapeake Bay and (2) the functional response (food intake rate for different prey sizes, densities, and depth in substrate). With this information, we will attempt to model the foraging energetics of these species in response to changes in prey density, size, and depth in substrate (Richman and Lovvorn 2002).