Human activities may restrict access of wintering birds to their food resources, but habitat destruction and fragmentation may interact with disturbance to reduce carrying capacity. We analysed the abundance and distribution of wintering Brent Geese (Branta bernicla) in a major French wintering site from 1970 to 2000, when they experienced increases in human foreshore activities. We used mixed-effects models to test whether spatial extent of two Zostera species, Z. noltii and Z. marina, influenced the distribution of Brent Geese. The number of geese increased significantly with the area of both Zostera species beds. However, the relationship changed in the period after the increase in human activities. More specifically, fragmentation of the most accessible food resource, Z. noltii, negatively affected Brent Goose distribution. This fragmentation was in turn increased by human activities and reduced by the protection of Z. noltii (by banning human access). This implies that direct disturbance, although not excluded, might not have been the major cause of changes in Brent Goose distribution, but rather the effects of human activities on food resources. Thus, our results show that establishment of resource protection areas are efficient as conservation measures, and they underline the need for studies of impacts of human activities on resources, in addition to disturbance effects.