Masters Thesis

Semi-colonial nesting in the snowy plover

Snowy Plovers (Charadrius nivosus) have been characterized as nesting semicolonially, which means nests are clustered (but to a lesser degree than for colonial species), so that suitable habitat nearby is unoccupied. I assessed the spatial pattern of nests for a color-marked population of Snowy Plovers breeding at low density (19-64 breeding adults per year for >780 ha) in coastal northern California, over a period of 12 years and at a landscape scale. I also investigated the effect of population size on nest clustering, the consistency of individual male plovers (that bred for 2+ years in the study area) in their degree of sociality (as measured by the nearest neighbor distances of their nests), and the effect of nearest neighbor distance on hatching success of nests. Mean nearest neighbor distance was 1,284 m (median = 182 m, SD = 4,019 m, range = 20- 41,519 m; n = 210 nests; 19% of nests were located <100 m from a neighbor’s nest). Nests were random in one year and semi-colonial in the remaining 11 years, six years of which nests were clustered and five years of which nests were marginally clustered. Nests were more clustered in years of high population size. Male plovers (n = 43) were not consistent in their degree of sociality. Finally, nearest neighbor distance was not related to a nest’s probability of hatching. Given that Snowy Plover nests were more clustered in years of high population size, I would expect that semi-colonial nesting would be even more prevalent elsewhere in their range where Snowy Plovers nest at higher density.