Weather, climate, and entry into migration of northern fur seal pups

In the migration of young animals, environmental cues can play an outsized role in dispersal, ontogeny, and potentially survival. Identifying and quantifying such cues promotes an understanding of individual species’ migratory evolution and response to long-term environmental change. This study examines weather as a proximate factor for initiating first migration in a wide-ranging subpolar marine predator, the northern fur seal (laaqudax̂, in Unangam Tunuu; Callorhinus ursinus (Linnaeus 1758)). Observations of satellite-telemetered pups on three islands in the eastern Bering Sea, Alaska (US) are used to quantify how inclement weather (high winds, snow, and low temperatures) increases departure rate. Historical weather is then used to reconstruct departure, from the mid-20th century onward. Contemporary surveys provide a test for reconstructed estimates and highlight behavioral processes near the entry to migration. Reconstructions provide novel climate context for large-scale population declines in the eastern Bering Sea since the 1950s; within their limitations, there is a lack of evidence for trends in departure or significant influence on demography. Results here build upon and support historical knowledge regarding the role of weather, while also highlighting potential areas of future study – such as maternal behavior – in influencing the entry into first migration in this species.