EFFECTS OF DIET COMPOSITION AND AMBIENT-TEMPERATURE ON FOOD CHOICE OFCAPTIVE MALLARDS

Six experimental diets were fed to 60 captive game-farm mallards (Anas platyrhynchos) housed in outdoor aviaries in Southeastern Arkansas du ring December 1990 to January 1991. Diet treatments were: 1) high-prot ein (27%) pellet (control diet nutritionally balanced for ducks), (2) low-protein pellet (control diet deficient in protein), (3) corn, (4) rice, (5) soybean, and (6) a natural diet, which represented foods ava ilable to wild mallards in the Mississippi Alluvial Valley during wint er. Birds fed the natural diet consumed the highest total mass of pell ets. Consumption of high- and low-protein pellets was similar (P great er than or equal to 0.12) regardless of the diet mallards were fed dur ing all six feeding trials. Soybeans contain digestion inhibitors. Des pite this, mallards maintained on soybeans did not increase intake abo ve that of birds consuming the five other diets, suggesting that consu mption of soybeans may decrease mallard appetite and thereby reduce da ily nutrient intake. Pellet consumption during feeding trials was also influenced by ambient temperature and food-pan placement. Negative en ergy balances, hunting or dominance pressures, and digestion-inhibitin g factors may all interfere with mechanisms to direct food choices. Th us, mallards apparently feed opportunistically on whatever food items become available.