Destruction of wetland habitats by lesser snow geese: a keystone species on the west coast of Hudson Bay.

SUMMARY (1) Large numbers of lesser snow geese breed in colonies in coastal brackish and freshwater marshes in the lowlands along the west coast of Hudson Bay. Where colonies are present, the geese determine the structure and species composition of the coastal plant communities. (2) During recent decades, substantial increases in the number of birds have occurred, resulting in the outward spread of the colonies into new areas which are used for nesting, feeding and moulting. (3) Patterns of foraging vary in space and time. In spring at the nesting sites, before the onset of above-ground growth of vegetation, adult geese grub for roots and rhizomes of graminoid plants in relatively dry areas, and in wet habitats they eat the swollen bases of shoots of sedges, particularly Carex aquatilis. In summer, adults and goslings graze intensively on leaves of grasses and sedges over wide areas. Swards dominated by Carex subspathacea are produced in brackish marshes, but the leaves of graminoids of the freshwater sedge meadows are also clipped extensively. (4) Grubbing of vegetation by geese each spring creates bare areas (1-5 mi2) of peat and sediment. The increased numbers of birds have increased the scale of disturbance, with large areas now stripped of vegetation, particularly by the McConnell River. At some sites, erosion of peat has exposed the underlying glacial gravels. There is little likelihood that the vegetation which re-establishes will closely resemble the original. Further expansion of goose colonies in this region may be limited by available food resources.