Breeding <i>Sternula antillarum</i> (Least Terns) disturbance distances and duration of escape behaviors: Pedestrians necessitate larger conservation buffers than do passing vehicles

ABSTRACT We tested the behavioral responses of breeding Sternula antillarum (Least Terns) to pedestrians and off-road vehicles and showed that disturbance source, intra-colony characteristics, and environmental factors all influenced the distance at which the birds were disturbed, as well as the duration of their response. Our goal was to inform wildlife buffer distances used to protect breeding S. antillarum at Cape Hatteras National Seashore, North Carolina, and beyond. We measured breeding S. antillarum behavioral responses to pedestrians and vehicles during routine activities at 8 colonies and during experimental activities at 3 colonies. Pedestrians caused the highest flush probability when walking directly towards a nest (Cox proportional hazard models: cumulative risk = 1 at both 100 m and 50 m) and lowest when walking past a nest (cumulative risk = 0.14 at 100 m and cumulative risk = 0.54 at 50 m). Passing vehicles had the lowest probability of causing birds to flush, cumulative risk = 0.02 at all measured distances up to 25 m from the nest. We also applied generalized linear models to model the duration of responses and found that it was affected by the number of nests in a colony, the density of nests in a colony, nest life stage, nest clustering, date, degree of pivot of a disturbance source along its route, and nest distance from colony edge. These results suggest that conservation managers can reduce S. antillarum buffers in locations where there are less disturbing human activities or less reactive S. antillarum colonies.