Bioenergetics modeling is a popular tool used by waterfowl biologists to estimate carrying capacity based on food energy availability and daily energy expenditure (DEE). For wintering waterfowl, estimates of DEE may incorporate a cost of thermoregulation (CT) component, which accounts for metabolic heat production when ambient temperatures fall below a species-specific Lower Critical Temperature (LCT). Typically, DEE estimates have utilized either a fixed CT component or a simple CT model based solely on the magnitude of the difference between ambient temperature and LCT. Using a more complex CT model that accounts for differential heat loss from individual body regions due to temperature, wind speed, and contact with air or water may provide more detailed estimates of CT and, in turn, carrying capacity. However, such models required detailed morphometrics as model inputs in addition to environmental data. We present morphometrics for 8 dabbling duck species for use in thermoregulation models, as well as regression equations that may substitute for measurements of unmeasured species. We compared CT values produced via simple and complex CT models for American Black Ducks (Anas rubripes) wintering on the Delaware Bayshore, 2011–2013. We found that the complex CT model produced significantly higher CT estimates (5.38 ± SE 0.38 kJ bird−1 hr−1) compared with the simple model (1.26 ± 0.04 kJ bird−1 hr−1). Applying these CT values to bioenergetics models for American Black Ducks wintering in southern New Jersey suggested that this disparity in CT could produce substantial differences in estimated carrying capacity. Thus, we recommend that researchers consider incorporating detailed CT models into their estimates of DEE to reduce bias in carrying capacity estimates.
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Vol. 117 • No. 4