Spatial and temporal variation in spring diet of greater snow geese inferred from stable isotopes

Changes in diet or habitat use due to seasonal variations in food availability or anthropogenic activity can impact nutrient storage during migration. We assessed the diet of spring staging Greater Snow Geese in Québec (Anser caerulescens atlantica Kennard, 1927) at sites characterized by different habitats, and determined whether the diet changed over a 25-year period (1999-2001 vs 2021-2024). We analyzed stable isotopes (13C and 15N) in goose muscles, liver and abdominal fat, and food plants. Isotopes allowed determination of the goose diet although discrimination between marsh plants (Schoenoplectus and Spartina) and some plants consumed in farmlands was poor. Corn dominated the diet at Lac-St-Pierre but decreased as geese moved to other sites later during staging. In the Upper St. Lawrence estuary, Schoenoplectus, legumes (clover and alfalfa) and corn were the most consumed items. In the Lower estuary, diet was difficult to assess reliably. Annual variations in the diet were large and showed little temporal change over 25 years except for a possible reduction in Schoenoplectus and increase in legumes. We also detected an enrichment in 15N of food sources during that period. Our results show that goose diet is flexible in response to environmental changes and anthropogenic disturbance during staging.