Energy-Based Carrying Capacities of Bufflehead Bucephala albeola Wintering Habitats

摘要

We present a model for calculating energy-based carrying capacities for bufflehead (Bucephala albeola), asmall North American sea duck wintering in coastal and estuarine habitats. Our model uses estimates of the seasonalenergy expenditures that incorporate site-specific energetic costs of thermoregulation, along with available prey energydensities to calculate carrying capacities in numbers of birds per winter. The model was used to calculate carryingcapacities under several foraging scenarios for bufflehead wintering at three urban and three rural sites in the coastalnortheast U.S. We found that energy-based carrying capacities varied from 20 – 320 birds per site per winter (0.38 – 6.22birds per hectare), and showed a trend towards increasing with prey energy density (r = 0.53) and with decreasing averagedaily energy expenditure (r2 = 0.57, p = 0.08). We found greater prey species richness at rural sites, but similar preybiomass and productivity across all sites. Bufflehead density averaged 1.89 ± 2.34 birds per hectare (range 0.38 – 6.22birds per hectare) across the sites. Bufflehead abundance at urban sites was reduced by an average of 43.7% from thatpredicted using the relationship between per-hectare carrying capacity and bufflehead abundance at rural sites. Thisdifference may arise from natural or human induced factors that act to limit sea duck populations on wintering habitats.