Effects of nutrients on the physiology, energetics, and behavior of captive sea ducks relative to sea duck feeding ecology in Chesapeake Bay
Project Number: 34
Year Funded: 2005
Lead Institution(s): Patuxent Wildlife Research Center
Project Lead: Matthew Perry
Collaborator(s): Alica Wells-Berlin (USGS PWRC), USFWS, CWS
Location: Chesapeake Bay
Focal Species: Long-tailed Duck (Clangula hyemalis), Black Scoter (Melanitta americana), Surf Scoter (Melanitta perspicillata), White-winged Scoter (Melanitta delgandi)
Project Description: Summary reports on the status of seaducks have revealed that populations have declined for some species and there has been an increased concern for the status of seaducks in general (Elliot 1997; Kehoe 1994; Petersen and Hogan 1996). Surveys of seaducks wintering on the Atlantic coast (1991-99) have shown major declines for the long-tailed duck (Clangula hyemalis), black scoter (Melanitta nigra), and surf scoter (M. perspiculla), whereas, the white-winged scoter (M. fusca) remained stable (Caithamer et al. 2000).
The Chesapeake Bay is an important wintering area for the three scoter species and the long-tailed duck. However, the Chesapeake Bay has undergone extensive changes in the food sources it offers wintering waterfowl due to water quality changes. The availability of food resources to ducks is especially important in areas of the Chesapeake Bay at depths of 10-30 feet where seaducks typically feed. These areas may be the first to be impacted by anoxic conditions if poor water conditions occur during the summer months. As the quality and (or) quantity of food declines, ducks may travel farther between suitable food items or food patches to maintain adequate energy/nutrient intake. The food taken at any one time depends on both the preferences of the ducks and the availability of the food items. Thus as the availability of any food item changes, the food habits and possibly the relative abundance of the ducks may change, and result in movement into or away from an area.
In addition, if a food organism is present below a certain density it may no longer be profitable in terms of energy gain for a duck to seek it (Sugden 1971) so it may cause the duck to switch to a more abundant lower energy food source. The rate of acquisition of energy and nutrients depends on the intake rate of food items, and the food’s size, nutrient content, and digestibility (Richman and Lovvorn 2002, 2003). Change in intake rate with prey density is a basic component of a number of models of waterbird foraging (Richman and Lovvorn 2002, 2003). A type II functional response, in which intake rates increase with increasing prey density up to an asymptote, often typifies diving duck foraging on benthic foods (Takekawa 1987, Giles 1990, Lovvorn and Gillingham 1996, Richman and Lovvorn 2002).
The Chesapeake Bay is an important wintering area for the three scoter species and the long-tailed duck. However, the Chesapeake Bay has undergone extensive changes in the food sources it offers wintering waterfowl due to water quality changes. The availability of food resources to ducks is especially important in areas of the Chesapeake Bay at depths of 10-30 feet where seaducks typically feed. These areas may be the first to be impacted by anoxic conditions if poor water conditions occur during the summer months. As the quality and (or) quantity of food declines, ducks may travel farther between suitable food items or food patches to maintain adequate energy/nutrient intake. The food taken at any one time depends on both the preferences of the ducks and the availability of the food items. Thus as the availability of any food item changes, the food habits and possibly the relative abundance of the ducks may change, and result in movement into or away from an area.
In addition, if a food organism is present below a certain density it may no longer be profitable in terms of energy gain for a duck to seek it (Sugden 1971) so it may cause the duck to switch to a more abundant lower energy food source. The rate of acquisition of energy and nutrients depends on the intake rate of food items, and the food’s size, nutrient content, and digestibility (Richman and Lovvorn 2002, 2003). Change in intake rate with prey density is a basic component of a number of models of waterbird foraging (Richman and Lovvorn 2002, 2003). A type II functional response, in which intake rates increase with increasing prey density up to an asymptote, often typifies diving duck foraging on benthic foods (Takekawa 1987, Giles 1990, Lovvorn and Gillingham 1996, Richman and Lovvorn 2002).
Project Reports: https://seaduckjv.org/pdf/studies/pr34.pdf