Declining Scaup Populations:
Issues, Hypotheses, and Research Needs
Examine use, distribution, and role of food resources relative to body condition and reproduction
Closely linked to contaminant issues are feeding ecology and acquisition of necessary nutrient reserves for reproduction. Scaup's ability to reproduce successfully may be limited by food resources, nutrient availability, or nutrient reserves during any portion of the life cycle (A. D. Afton, United States Geological Survey, and M. G. Anderson, Ducks Unlimited Canada, unpublished data; Austin et al. 1999). It is largely unknown when or where critical reserves for breeding are acquired by female scaup or to what degree body condition impacts reproductive success. Some preliminary information exists for lesser scaup breeding in prairie parklands (Afton and Ankney 1991; A. D. Afton, United States Geological Survey, unpublished data). Changes in food quality and quantity on wintering and migration areas may differentially impact nutrient reserve dynamics and ultimately the condition of scaup upon arrival at different breeding areas (A. D. Afton, United States Geological Survey, and M. G. Anderson, Ducks Unlimited Canada, unpublished data).
Studies examining nutrient-reserve dynamics, food habits, and habitat use during spring migration are needed to fill this information gap. We recommend collection of foraging scaup, targeting primarily females, throughout the annual cycle to study acquisition of nutrient reserves and to determine food habits; these studies also should assess food availability. These data are most needed for coastal areas and for spring migration through Canada. A suite of studies could compare nutrient-reserve dynamics and foraging ecology among flyways, among populations that breed east versus west of the Continental Divide, or between boreal forest and prairie parkland populations. Information on affiliations among wintering, migration, and breeding areas will be important to design these studies. In addition, we recommend developing energetics models for lesser scaup during their life cycle, including thermoregulation, nutrients, cost to capture and process food, human disturbance, and effects of hunting activities, to understand more completely the factors affecting nutrient-reserve dynamics and needs.
Stable isotope analyses also could provide information on foraging ecology, including nutrient reserve dynamics or food resources and can help identify breeding areas (Chamberlain et al. 1997). Initially, research is needed to determine whether stable isotopes will answer nutrient or food resource questions or identify breeding areas and, if so, which isotopes would be appropriate. Stable isotope data could be obtained readily through ongoing studies where scaup are collected or captured.
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