Spatial and temporal unpredictability of colony size in cliff swallows across 30 years

Most colonially breeding animals occupy colonies that range in size from a few pairs to thousands of individuals, but the causes of colony size variation are largely unknown. Three general hypotheses are: (1) that variation in colony size is maintained by fluctuating selection via spatial and temporal changes in fitness associated with different colony sizes; (2) that colony formation reflects heterogeneity in habitat, with some sites having resources to support more individuals than others; and (3) that individuals assess the presence or annual reproductive success of current colony residents at each site and aggregate preferentially at high-quality sites. These hypotheses make predictions about how consistent colony size should be across sites and among years. We examined temporal and spatial variability of colony size for >200 Cliff Swallow (Petrochelidon pyrrhonota) colony sites in western Nebraska across a 30-year period. A colony's substrate type, annual population size in the ...