Biomechanics and foraging profitability: an approach to assessing trophic needs and impacts of diving ducks
- Department of Zoology and Physiology, University of Wyoming, 82071, Laramie, Wyoming, USA
A biomechanical model of underwater locomotion is described, and data required by the model presented for 3 species of diving duck (Aythya spp.). Based on field observations of behavior and foods consumed, the model is used to estimate energy costs of foraging and minimum food intake rates of canvasbacks (Aythya valisineria) in two habitats in North Carolina. Increased water depth from 0.5 m in Lake Mattamuskeet to 1.5 m in Pamlico Sound increased the net cost of time spent foraging at the bottom by 43%. Biomechanical calculations are combined with data on intake rates at different food densities (Takekawa, 1987) to determine minimum food densities for profitable foraging in Lake Mattamuskeet. Field observations of behavior are used to adjust minimum intake per dive for unsuccessful dives spent locating food patches. Density and dispersion of plant tuber foods in Lake Mattamuskeet, before and after the fall staging period, suggest that the fraction of habitat with tuber densities above a profitability threshold is more critical to canvasbacks than average tuber density. Such factors are important in relating bird energy requirements and benthic sampling data to carrying capacity and total area of usable habitat. The proportion of foods that can be fed upon profitably also determines the fraction of food organisms subject to depletion as components of trophic pathways.
- 1 - sciences appliquees, technologies et medecines
- 2 - sciences biologiques et medicales
- 3 - sciences biologiques fondamentales et appliquees. psychologie
- 4 - ecologie animale, vegetale et microbienne