The feeding ecology of northern pintails (Anas acuta) and green-winged teal (A. crecca) was examined from October through February 1979-81 in 4 major seasonal marsh types in the Central Valley, California. The esophagi of 262 pintails contained 72.3% plant seeds and 27.7% animal matter. The esophagi of 173 green-winged teal contained 62.3% plant seeds and 37.6% animal matter. Swamp timothy (Heleochloa schoenoides) caryopses, chironomid midge larvae, and common barnyardgrass (Echinochloa crusgalli) caryopses formed >50% of the diet of both species. Both species were highly opportunistic and generally shifted their food habits seasonally to the most available foods. Animal matter increased seasonally in the diets of both and formed about 60% of the foods eaten during January and February compared to only about 8% in October and 17% in December. Both species used open water marsh habitats almost exclusively in daytime but they used densely vegetated marshes almost exclusively at night. Management recommendations based on the food habits and habitat use patterns of pintails and green-winged teal are offered.