Environmental variation at multiple stages of the annual cycle influences survival of a migratory songbird: a study over three decades

Understanding population dynamics of wild animals requires robust estimates of survival, as well as knowledge of factors that drive variation in survival. We used 30 years of capture-recapture data from a Savannah sparrow (Passerculus sandwichensis) population on Kent Island, New Brunswick to examine how environmental factors influenced apparent annual survival. Adult male annual survival was negatively related to early-winter freeze days and positively related to temperature during multiple periods and winter food abundance. Adult female survival was positively related to early-winter temperature and negatively related to late-winter freeze days. Juvenile male survival was positively related to post-breeding precipitation and negatively related to early-winter precipitation, whereas juvenile female survival was negatively related to breeding precipitation and late-winter freeze days, and positively related to winter food abundance. Our results suggest winter conditions are primary drivers of survival, but factors during other periods can also affect survival for specific age and sex classes.