Habitat selection and optimal foraging by mallards : a field experiment / John P. Ball

Both habitat structure and food in a large cattail (Typha spp.) marsh were experimentally manipulated to determine if breeding mallards (Anas platyrhynchos) selected habitat using one or both of these factors.Forth openings (patches of open water in dense cattail) of size 0.02,0.09 or 0.15 ha were created by burning and cutting cattail at the St.Clair National Wildlife Area in southwestern Ontario in 1982 and 1983.The results indicated that mallards selected habitat on the basis of opening size and food (as estimated by the total dry biomass of aquatic invertebrates). I also assessed how mallards allocated their foraging effort across 40 patches of differing food abundance. The ranking of patches was not the same over time, so mallards had to sample the patches to gain information on food distribution. Mallards did not exhibit the classic all or none use of patches predicted by some optimal foraging models, but instead allocated foraging effort as a continuous function of patch pr