Adult survival in a small seabird, Hydrobates leucorhous, covaries with the Atlantic Multidecadal Oscillation over the past six decades.

Seabirds' annual survival is influenced by numerous factors, but oceanic conditions are among the most significant. Indices used to monitor these conditions typically cycle over decades. Using the longest capture-mark-recapture (CMR) time series available for the species (1955-2023), we estimated apparent adult survival of Leach's storm-petrels (Hydrobates leucorhous) from Kent Island, New Brunswick. We assessed whether survival covaried with large-scale oceanographic indices reflecting conditions at various periods in the life cycle. We used Cormack-Jolly-Seber CMR models to estimate the annual apparent survival rate. Mean annual survival was φ = 0.84 ± 0.01 over the 68-year study period, and was variable across years (range: 0.62 ± 0.06 to 0.97 ± 0.05) with a concentration of high values between 1979 and 1989. Adult survival rate was inversely proportional to the Atlantic Multidecadal Oscillation (AMO) index with a small but significant effect (β: -0.70 [-0.92 to -0.47], 13% of deviance explained), meaning low survival rates were associated with high AMO and indicating positive sea surface temperature anomalies over the North Atlantic. Such a relationship could only have been detected with extended long-term study since the AMO has a period of 60-80 years. Despite the challenges of maintaining long-term studies, they are more than ever essential in population ecology.