Conspecific attraction in the breeding distribution of the Western Snowy Plover (Charadrius alexandrinus nivosus)

I examined evidence that conspecific attraction influenced the spatial distributions of Western Snowy Plovers (Charadrius alexandrinus nivosus) breeding in coastal northern California over 6 years. Most (85%) yearlings and immigrants first nested in the study area at occupied sites. This produced a significant positive correlation between the abundance of experienced plovers and recruitment of naive plovers at 16 breeding sites. At the site with the most breeding plovers, nests were clustered within suitable habitat. Spatial variation in habitat features (i.e., beach width, debris, vegetation cover), and indices of predators and human activity explained less of this aggregated pattern than variation in nest density in previous years. Plovers often (males: 86%, females: 67%) nested in the same areas in consecutive years. Moreover, at the time they initiated clutches, most plovers nested closer to conspecifics than expected by chance. These results suggest that the likelihood of success of management actions (i.e., habitat restoration) to recover the population of this threatened species may hinge on social stimulation to encourage plovers to (re)colonize historical breeding sites. And, if plovers cue on conspecifics to assess the quality of breeding sites, then the use of predator exclosures to increase nest success could mislead naïve individuals into settling in sub-optimal habitat.