Annual variation in distance to nearest neighbor nest decreases with population size in Snowy Plovers
215 – 224
26 December 17
Allison M.K. Patrick, Mark A. Colwell
Wildlife Department, Humboldt State University, Arcata, CA 95521, USA
In non-colonial species, the spatial pattern in which nests occur in a population often varies among years and with habitat quality and population size. In aggregated patterns nests occur nearer than expected by chance and apparently suitable habitat remains unoccupied. We assessed annual (12 years) and spatial (10–100 km) variation in nest dispersion using distance to nearest conspecific nests for a small, color-marked population (19–64 adults annually) of Snowy Plover Charadrius nivosus breeding in coastal northern California. Across 100 km of suitable habitat, average distance to conspecific nest was 1,284 m (median = 182 m, SD = 4,019 m, range = 20–41,519 m, n = 210 nests); 19% of nests were <100 m from a conspecific’s nest. When we restricted analyses to a 10-km beach where more plovers consistently bred, average distance to nearest nest decreased. Plover nests were aggregated in 11 of 12 years; the one exception occurred when local population was lowest. For marked males (n = 43) that bred in multiple years (range: 2–10), there was no evidence that individuals consistently nested near conspecifics. These results suggest that breeding aggregations may be more prevalent near the core of the species’ range where populations are larger, and they serve as a cautionary reminder of the challenges of estimating population size based on extrapolations derived from areas of high breeding density to unsampled, but seemingly suitable, habitat.