Response of nesting savannah sparrows to 25 years of habitat change in a snow goose colony

Duplication of a study conducted 25 years earlier reveals that the number of savannah sparrows nesting adjacent to the coastal salt marshes of La Perouse Bay in northern Manitoba, Canada, has declined by 77%. This decline coincides with a 63% reduction in vegetation cover in the-bird's preferred grassland-shrub habitat. The habitat degradation resulted from processes associated with destructive foraging by the increasing mid-continent population of lesser snow geese during their breeding season. Growth of this snow goose population has been initiated and sustained by a series of anthropogenic factors operating primarily on the snow goose wintering grounds, far south of these Arctic coastal habitats. Thus, the indirect human impact on nesting-by savannah sparrows is the result of a complex chain of ecological events operating on connected habitats across a large geographical expanse. Mitigation of such effects and an assessment of the impacts in general must take into account such complexities.