Incubating snowy plovers (Charadrius nivosus) exhibit site-specific patterns of disturbance from human activities

Context Many shorebirds are threatened by human-caused disturbance. For snowy plovers, disturbance within nesting habitats has been implicated as a major contributing factor in their population decline through deleterious effects on breeding success. Very little is known about site specificity of disturbance from human activities for this species. Aims We examined the disturbance of incubating snowy plovers to determine if nesting shorebirds within one breeding population exhibited site-specific patterns of disturbance from human activities. Methods We recorded flush (i.e. flight or escape from a perceived threat) distances and time spent off the nest following approach by a single person on Sanibel and Cayo Costa Islands, two islands in south-west Florida that differ in daily human visitation, and by a person walking a dog on Sanibel. We used a Bayesian model framework to determine effects of location and approach type on flush distance and time spent off of the nest. Key results Birds nesting on Sanibel flushed at shorter distances from a solitary person without a dog than did birds nesting on Cayo Costa, but spent similar amounts of time off of nests following a flush. On Sanibel, nesting birds also flushed at significantly greater distances and spent significantly more time off of nests when flushed by a person walking a dog rather than by a person alone. Conclusions Within a population, nesting snowy plovers exhibit site- and stimulus-dependent patterns of disturbance. The intraspecific variation falls within the range of variation recorded among species of birds studied elsewhere. Although we cannot determine causation, we suggest habituation to human activities from a combination of high beach usage, smaller nesting exclusion zones, and narrower beach width on Sanibel compared to Cayo Costa as a likely explanation for this difference. Implications Set-back distances for symbolic fencing have been generalised across species and nesting locations. Our results suggest that disturbance of nesting shorebirds can be site-dependent even within one breeding population of a species. Set-back distances around shorebird nests must account for location and types of activities encountered, implying the need for more conservative implementation of set-back distances.