Breeding snowy plovers (Charadrius alexandrinus) exhibit variable response to human disturbance on two islands in southwest Florida

Human disturbance has been implicated in population declines and decreased productivity in shorebirds, including the Snowy Plover, around the world. In this study, we examined the response of Snowy Plovers nesting on two islands in southwest Florida, Sanibel and La Costa Islands, to human disturbance. We recorded flush distances and time spent off the nest for incubating birds in response to approach by a human on both Sanibel and La Costa, and for approach by a leashed dog on Sanibel only. We also recorded the first reaction distance of Snowy Plover adults and broods to approach by a human on both islands, and activity budgets of adults and chicks in the presence and absence of human activity. We conducted Bayesian analyses on all approach data. We used Principal Component Analysis, followed by Multivariate Analyses of Variance on activity budget data to examine the effect of people on bird behavior. We found that incubating birds on Sanibel flushed at significantly shorter distances from a person than did birds on La Costa; additionally, we found that Sanibel birds flushed at significantly greater distances from a dog than from a person. For time off nest, we found that birds remained off a nest for a significantly longer period of time following a flush by a dog than by a person; no difference between birds nesting on Sanibel and La Costa, however, was observed for time off nest. Brood reaction distance remained constant over the pre-fledged period and did not differ between broods that fledged and those that did not. We found that broods from La Costa reacted to human disturbance at greater distances than did broods on Sanibel. Additionally, human presence, regardless of activity type, resulted in altered behavior of Sanibel Snowy Plovers. In particular, running and foraging behaviors decreased, while walking increased. Beach driving vehicles also resulted in altered behavior of Sanibel Island broods. The presence of vehicles resulted in increased sitting and decreased standing.