Habitat use by waterfowl wintering in Narragansett Bay, Rhode Island

Coastal areas near urban centers often provide waterfowl habitat, but little is known of the effects of human development on wintering waterfowl. We used energetic and modeling approaches to examine habitat use by wintering waterfowl along a gradient of human disturbance in an urban estuary in the northeast U.S. Using estimates of the energetic costs of thermoregulation and different behaviors, we developed a model to estimate daily energy expenditure (DEE) of wintering buffleheads (Bucephala albeola) at six sites in Narragansett Bay, RI. Bufflehead DEE ranged from 46.9--52.4 kJ/hr, and energetic costs of thermoregulation comprised as much as 28% of their total DEE. We then used the DEE model to estimate energy-based carrying capacities for six bufflehead wintering habitats. Energy-based carrying capacities varied from 20--320 birds per site per winter, and decreased with increasing average daily energy expenditure (r2 = 0.57, P = 0.08). At the same sites, we observed bufflehead abundances that were much lower than our estimated carrying capacities (average 7.3--37.4 birds per site), which suggested that there may be other natural or human-induced factors that are acting to limit habitat use. We used several modeling approaches to examine the effect of a sub-set of these factors on waterfowl abundance at these and 26 additional sites chosen along a gradient of human development in Narragansett Bay, as well as 24 Harlequin duck (Histrionicus histrionicus) wintering sites in southern New England. Hunting activity and habitat characteristics explained 13--27% of the variation in waterfowl abundance and species richness between sites, and adding landscape characteristics explained an additional 1--26%. Wetland area, proportion of vegetated land, and the extent of residential development were the most common variables entering into the models; most species were more abundant in landscapes with more wetland and vegetated land and less residential development. Our findings suggest that human development may be among the factors affecting habitat use by waterfowl wintering in urban estuaries, and conservation strategies that set development thresholds for coastal habitats should be considered to help protect remaining waterfowl habitat in North Atlantic estuaries.