Many aspects of the reproductive ecology of seabirds are linked to the phenology, quantity and accessibility of marine food supplies. In polar regions, annual sea ice constrains these aspects of marine productivity, and thus seabirds breeding at high latitudes may exhibit adaptations to accommodate these constraints. Like most petrels, northern fulmars Fulmarus glacialis undertake an exodus from their breeding colony just before egg-laying. To assess whether this exodus was related to energetic needs and stored nutrient reserves, we studied changes in body mass and composition of male and female fulmars breeding in the Canadian High Arctic, by comparing birds collected just before and just after the pre-laying exodus. Males gained body mass over this period, accumulating water, fat and protein, whereas females lost body mass, particularly protein and fat. Declines in female fat and protein approximated the amounts contributed to eggs, but water and mineral reserves in pre-exodus females appeared insufficient for egg production. We hypothesize that female fulmars leave the colony before egg-laying to meet mineral demands for egg production, possibly focusing on calcium-rich prey. In contrast, we hypothesize that males use a different strategy for resource acquisition and allocation, which seeks to maximize fat and protein accumulation to meet forthcoming incubation demands. Differences in typical marine environmental conditions at breeding colonies across the species' range probably account for observed behavioral variation in breeding schedules, and may also result in different nutrient dynamics.