Legacy effects of habitat degradation by Lesser Snow Geese on nesting Savannah Sparrows

Abstract

Increased growth of the midcontinental population of Lesser Snow Geese(Chen caerulescens caerulescens) has led to overgrazing and habitatdegradation at their Arctic and sub-Arctic breeding grounds. Thishabitat degradation has been shown to induce a trophic cascade thatnegatively affects plant, insect, and other avian species that sharethese habitats. In conjunction with a long-term study of the impacts ofLesser Snow Geese on habitat, we examined the dual influences of climateand long-term habitat change on the nesting occurrence of SavannahSparrows near Churchill, Manitoba, Canada. Using multistate occupancymodels, we found that variability in early-summer temperature andprecipitation modulated year-to-year variability in nesting occurrenceand detection probabilities. Extreme warm and wet conditions in earlysummer can benefit breeding Savannah Sparrows across the landscape.However, such events have not been prevalent enough to override thesimilar to 80{%} decline in Savannah Sparrow nesting occurrence over 36yr. This dramatic decline can be attributed to the legacy of Lesser SnowGoose foraging, which has led to an 84{%} reduction in preferred shrubhabitat for nesting Savannah Sparrows. Management actions targeted atreducing Lesser Snow Goose abundance and habitat restoration will beneeded to allow sympatric Savannah Sparrows and functionally similarspecies to recover.