Temporal change in the contribution of immigration to population growth in a wild seabird experiencing rapid population decline

The source-sink paradigm predicts that populations in poorer-quality habitats ("sinks") persist due to continued immigration from more-productive areas ("sources"). However, this categorisation of populations assumes that habitat quality is fixed through time. Globally, we are in an era of wide-spread habitat degradation, and consequently, there is a pressing need to examine dispersal dynamics in relation to local population change. We used an integrated population model to quantify immigration dynamics in a long-lived colonial seabird, the black-legged kittiwake Rissa tridactyla, that is classified as globally "Vulnerable". We then used a transient life table response experiment to evaluate the contribution of temporal variation in vital rates, immigration rates, and population structure to realised population growth. Finally, we used a simulation analysis to examine the importance of immigration to population dynamics. We show that the contribution of immigration changed as the population declined. This study demonstrates that immigration is unlikely to maintain vulnerable sink populations indefinitely, emphasising the need for temporal analyses of dispersal to identify shifts that may have dramatic consequences for population viability.