FOODS USED BY MALE MALLARDS WINTERING IN SOUTHEASTERN MISSOURI

Although winter foods of mallards (Anas platyrhynchos) have been docum ented in several studies, the importance of ecological or biological f actors on the consumption of specific food groups often was ignored. C onsequently, we evaluated whether age, pair status, molt status, habit at, year, or season influenced foods consumed by male mallards in sout heastern Missouri during winters 1983-86. Seeds of moist-soil plants c omposed 61.4 and 46.0% of the aggregate dry mass diet of ducks collect ed in 1983-84 and 1984-85. Agricultural grain made up 33.8% of the agg regate dry mass diet in 1984-85, and acorns accounted for 54.5% of the diet in 1985-86. Our analysis revealed that habitat where birds were collected (P < 0.01) and annual variation (P < 0.01) were predominate factors influencing male mallard diet during winter. We attribute annu al differences in food consumption primarily to annual variation in ma st production. Invertebrates were present in 82% of 156 food samples, but composed only 7.3% dry mass of all ducks collected. Invertebrate c onsumption was greater during mid-winter than during other portions of winter (P < 0.01), probably a result of population growth and life hi story strategies of invertebrate species. Consumption of food groups d id not differ among adult and immature males (P = 0.75), paired and un paired males (P = 0.15), or males of different molt status (P = 0.22). These results suggest that age and physiological factors are less imp ortant than environmental factors in determining food use by male mall ards during winter. Providing a diversity of habitats and suitable foo ds may be the best management approach to compensate for annual variat ion in availability of individual food resources.