A multi-level study of human recreational activity and least tern (Sterna antillarum) responses: Hatching success, behavioral responses, and stress hormone levels

Abstract

In New Jersey, Least Terns (Sterna antillarum) nest primarily on sandy ocean beaches, where they must often share their breeding space with beach recreationists. The goal of this study was to determine whether hatching success, behavioral responses, or stress hormone levels in nesting Least Terns vary with exposure to human recreational activity. In particular, I was interested in knowing if birds exposed to more frequent activity exhibit elevated responses or if they habituate to human activity, and whether any such changes have consequences for hatching success. I quantified human activity at multiple sections of beach at a single site where human activity varied with distance from public entrances. Birds were observed for several behavioral responses and were subjected to a capture-stress protocol to measure adrenocortical stress responses. There was no clear relationship between human activity and hatching success. Although a significant negative relationship was found for birds laying early in the season, it was heavily dependent on a single nest. Hatching success was influenced mainly by lay date, due to gull predation on late-nesting birds. Behavioral responses were related to human activity levels. Nests in areas of high human activity had a significantly higher probability of flushing in response to human approaches and were left exposed more frequently than nests in low activity areas. Neither nest failure (all causes combined), nor nest predation specifically, was related to flush probability or frequency of nest departures. Thus the increased flushing did not appear to be sufficient to decrease hatching success. Whether flush rates experienced at beaches with higher traffic would reduce hatching, and whether chick survival is affected differently by such exposure, remain open questions. Successful nests were more aggressively defended than nests that failed. No relationships were found between human activity levels and stress hormone levels, but few birds were trapped (N = 12) and power to detect patterns was likely low. Given that behavioral responses were elevated over the relatively low levels of traffic observed at this beach, and that the consequences of such increases are not fully understood, there should be some sites where recreation is prohibited.