Spatial structure, dispersal, and management of a recovering raptor population

Most wild species experience considerable variation in habitat quality. Ecological theory that considers how organisms disperse between good and bad habitats has shown that such spatial structure can strongly influence population dynamics, but real-world implications have rarely been found. In this study, researchers from the University of California Santa Cruz show that the spatial structure of Peregrine Falcons in California has profoundly influenced the management and recovery of this species.

California peregrines suffered a dramatic population crash in the 1950s due to DDT-induced eggshell thinning, and this regional population has been highly managed by the introduction of over 800 young birds. Observations of banded birds showed that dispersal rates between three subpopulations–interior, coastal, and urban–were asymmetric, with essentially no dispersal out of the interior subpopulation and a strong tendency for coastal peregrines to disperse to the urban habitats. By fitting regional population models to the observed recovery of breeding pairs in each habitat, this study also characterized the demographic performance of peregrines within each subpopulation.

The spatial structure revealed by this study suggests that the highly productive interior subpopulation would have recovered largely on its own, without the reintroduced birds, while the coastal subpopulation would have been very slow to recover without the reintroduction effort. This study makes clear that understanding spatial structure can be critical for the effective conservation and management of animal populations.