Food habits of northern pintails (Anas acuta) were investigated on 3 national wildlife refuges in the western portion of the Sacramento Valley, California, from August to March 1979-82. Pintails consumed >97% (aggregate % dry wt) plant food during diurnal foraging on national wildlife refuge rice, summerirrigated, and summer-dry habitats from August through January. Invertebrate use increased to 28.9-65.6% of the diet in these habitats during February and March. Rice, swamp timothy (Heleochloa schoenoides), flatsedges (Cyperus spp.), common barnyardgrass (Echinochloa crusgalli), southern naiad (Najas guadalupensis), and smartweed (Polygonum spp.) seeds, miscellaneous vegetation, snails (Gastropoda), and midge (Diptera) and water beetle (Coleoptera) larvae were most important. These foods usually were taken proportional to or greater than availability. Rice was the most important food of pintails feeding nocturnally off the refuges in harvested rice fields from October through January (99.7%) and February and March (63%; barnyardgrass formed 31% of the diet). In August and October, some pintails consumed invertebrates or bulrush (Scirpus spp.) seedlings in marshes soon after feeding in refuge rice (Aug) or harvested commercial rice fields (Oct), thereby increasing dietary protein. In late winter, females and males obtained similar (P > 0.05) percentages of invertebrates from refuge habitats. Important dietary seeds and invertebrates contained high protein or metabolizable energy content. Management should maintain adequate seed production in fall and mid-winter and invertebrate biomass in late winter. J. WILDL. MANAGE. 51(2):405-414 Northern pintails begin to arrive in the Sacramento Valley, California, from northern breeding and staging areas the 1st week of August. About 315,000 pintails are present by midSeptember (LeDonne 1980) and >1.5 million in January (LeDonne 1981); many remain through March. This large number of ducks present over this extended time period represents a significant demand for food resources. About 96% of the original marsh present in the Central Valley (the Sacramento Valley forms the northern half of the Central Valley) has been converted to other uses including rice farming. Waste grain left after harvest is an important waterfowl food (Gilmer et al. 1982). However, the importance to waterfowl of seeds and invertebrates from remaining marshes must be understood to manage food resources in Sacramento Valley wetlands. The role of winter food supply in the dynamics of waterfowl populations is poorly understood, but winter habitat conditions may affect recruitment (Heitmeyer and Fredrickson 1981). Recently, Beam and Gruenhagen (1980), Connelly and Chesemore (1980), and Euliss (1984), using esophageal samples, demonstrated significant use of invertebrates by pintails during winter in the San Joaquin Valley (the southern half of the Central Valley). However, food habit data available for Sacramento Valley waterfowl were collected in the 1940's and 1950's and were based almost entirely on analysis of gizzard contents (Calif. Dep. Fish and Game, Sacramento, and U.S. Fish and Wildl. Serv. [1954], unpubl. rep., Willows, Calif.). Such analyses were biased toward hard seeds (Dillon 1958, Swanson and Bartonek 1970). Specific foods consumed and their availability in the environment were not compared. Therefore, I used esophageal analysis to investigate foods consumed by northern pintails during late summer, fall, and winter in the Sacramento Valley. My objectives were to determine food preference and to describe seasonal variation in consumption of specific items relative to habitat types and behavioral and nutritional requirements. I thank the following people for their critical review of the manuscript: J. M. Hicks, G. L. Krapu, P. A. Opler, S. L. Paulus, K. J. Reinecke, T. L. Shaffer, and G. A. Swanson. D. S. Gilmer gave administrative and technical support and provided detailed review and helpful comments. J. H. Day, J. M. Hicks, S. R. Lawry, C. A. Lefever, D. L. Orthmeyer, and D. C. Weinrich processed esophagus and habitat samples. J. Ruckman of the Agron. Dep., Univ. California, Davis, provided protein analyses of seeds. J. J. Chesi, S. M. Dobbins, and B. J. Hass of the Calif. Dep. Food and Agric. identified many seeds. I thank J. B. Helvie, J. S. Miller, and J.