Foods consumed by 117 mallards (Anas platyrhynchos) collected on the breeding grounds of south-central North Dakota during spring and summer 1974-80 were examined. Animal foods accounted for 38 and 37% of the diet of paired males and nonlaying females, respectively (N = 80). The diet of laying females consisted of 72% animal foods, which differed significantly from that of paired males and nonlaying females. Insects, gastropods, crustaceans, annelids, and seeds made up 27.1, 16.4, 12.9, 12.8, and 24.8% of the diet, respectively, of laying females (N = 37). J. WILDL. MANAGE. 49(1):197-203 The prairie pothole region of North America contains a high density of shallow wetland basins with biotic communities that have developed under the influence of glaciation and a semiarid climate. Annual moisture deficits vary in magnitude and are accompanied by changes in water levels and dissolved salts (Stewart and Kantrud 1971, Swanson et al. 1974b). Plant and animal communities continually change in response to fluctuations in water level and salt content, and periodic droughts produce major changes in wetland biotic communities (Swanson and Meyer 1977). The dynamic nature of this water regime, and the periodic changes in the biota that it produces, is a dominant factor influencing the food base available to breeding waterfowl. Superimposed on the dynamic water regime of the prairie pothole region are tillage practices that can alter seasonally flooded wetlands annually and semipermanent wetlands during drought years. Tillage alters the food base of low prairie, wet meadow, and shallow marsh zones and is a major factor interacting with hydrology to influence biotic succession and, consequently, food availability. The high rate of nest destruction experienced by ground-nesting ducks in the prairie pothole region (Kirsch 1969, Higgins 1977) requires persistent renesting by mallard females if they are to achieve reproductive success. With each renesting effort and subsequent loss in body reserves, the food base available to breeding females increases in importance (Swanson et al. 1979). Foods consumed by laying mallards on the breeding grounds have not been identified. Perret (1962) described foods consumed by mallard females, but the reproductive status of the birds was not reported. Some preliminary results of foods consumed by laying mallards were discussed by Swanson et al. (1979). Studies of wetland ecology, mallard feeding ecology, and mallard renesting characteristics were undertaken concurrently in the prairie pothole region of south-central North Dakota to assess the ecological relation between breeding birds and their aquatic habitats. The purpose of the present paper is to describe foods consumed by laying female mallards on the breeding grounds of south-central North Dakota and compare these with foods of paired nonlaying females, paired males, and birds in