Among-colony synchrony in the survival of Common Guillemots Uria aalge reflects shared wintering areas

Spatiotemporal variation in survival may be an important driver of multi-population dynamics in many wild animal species, yet few scientific studies have addressed this issue, primarily due to a lack of sufficiently comprehensive and detailed datasets. Synchrony in survival rates among different, often distant, subpopulations appears to be common, caused by spatially correlated environmental conditions or by movement of animals from different sites such that their ranges overlap. Many seabird populations are effectively isolated during the breeding season because colonies are widely separated, but over the winter, birds disperse widely and there may be much mixing between different populations. The non-breeding season is also the period of main mortality for seabirds. Using mark–recapture and ring-recovery data, we tested for spatial, temporal and age-related correlations in survival of Common Guillemots Uria aalge among three widely separated Scottish colonies that have varying overlap in their overwintering distributions. Survival was highly correlated over time for colonies/age-classes sharing wintering areas and, except in 2004, was essentially uncorrelated for those with separate wintering areas. These results strongly suggest that one or more aspects of the winter environment are responsible for spatiotemporal variation in survival of British Guillemots, and provide insight into the factors driving large-scale population dynamics of the species.