Colonization and extinction dynamics of bank swallow ( Riparia riparia) colonies along the Sacramento River, California

I analyzed existing monitoring data of Bank Swallows (Riparia riparia), a threatened bird species in California, within a metapopulation context. I tested the relative importance of several temporal and spatial factors to the probability of colonization and extinction of active sites. I found strong support for a temporal trend in the colonization rate and for the importance of river discharge, weather, and the number of burrows at a site the previous year to the extinction rates. I conclude that this is not a simple metapopulation, because the temporal trend in the colonization rate may reflect habitat change, and the importance of within-population indices illustrates a need to understand population dynamics of individual colonies. The importance of temperature and precipitation may reflect prey availability, and river discharge may reflect erosion of active sites. The viability of this population remains unclear because the confidence limits around the current rates of colonization and extinction illustrate both, equilibrium and nonequilibrium dynamics, as well as metapopulation extinction. Most climate change scenarios favour the continuing existence of Bank Swallows in California.