RESEARCH ARTICLE


Energy-Based Carrying Capacities of Bufflehead Bucephala albeola Wintering Habitats



Richard A. McKinney*, 1, Scott R. McWilliams2
1 US Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, 27 Tarzwell Drive, Narragansett, RI 02882, USA
2 Department of Natural Resources Science, University of Rhode Island, Kingston, RI 02881, USA


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© 2012 McKinney and McWilliams

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: (https://creativecommons.org/licenses/by/4.0/legalcode). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the US Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, 27 Tarzwell Drive, Narragansett, RI 02882 USA; Tel: 401-782-3133; Fax: 401-782-3030; E-mails: mckinney.rick@epa.gov


Abstract

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

Keywords: Bufflehead Bucephala albeola, Energy-based carrying capacity, Habitat alteration, Narragansett Bay, Wintering waterfowl.