Decisions about habitat management for lesser snow geese (Chen caerulescens caerulescens) during spring migration are limited by the lack of information concerning their habitat use and diets. Consequently, we examined esophageal contents, habitat use, activity patterns, and feeding behavior of adult-plumaged snow geese from Oklahoma (Mar) to the coast of Hudson Bay (May), Ontario, in 1983-84. There were no sexual differences in spring diets. As snow geese moved northward, they switched from herbivory in Oklahoma and Nebraska to granivory in southern Manitoba. Agricultural foods, particularly corn, were more prevalent in snow goose diets than were natural foods during migration. Based on esophageal contents, granivory was more prevalent in prairie regions north of Oklahoma in 1983 than in 1984. Behavioral observations indicated that in southern Manitoba, more time was spent in corn fields in 1984 than in 1983. Natural foods were largely unused by geese until they reached the marshes of Hudson Bay, when consumption of green vegetation resumed. Moisture regimes in South Dakota and southern Manitoba influenced availability of roost sites which in turn was related to habitat use, percent of day flying, and dispersion of geese. Snow geese increased daily foraging time as migration proceeded. Reliance by snow geese on agricultural foods probably has reduced the annual variation in ability to acquire fat reserves on the prairies compared to times before agricultural development.