Evaluating the Response of Nonbreeding Shorebirds to Rate and Agents of Human Disturbance

Recreational disturbance is one of the major threats faced by shorebirds in the Western Hemisphere, especially during the non-breeding season. Between July 2016 and April 2017, shorebird surveys and behavioral observations were conducted at Bahía de Todos Santos, Baja California, Mexico. These data and generalized linear mixed models were used to assess whether (1) increased potential human disturbance resulted in lower shorebird abundance and (2) behavioral responses of shorebirds varied depending on the agent of disturbance (stimuli from human activities, e.g., people) and group size (e.g., number of people in the group). Shorebird abundance was modeled for all shorebirds combined and for three categories of body size (large, medium, small). Abundance of all, medium, and small shorebirds was negatively associated with potential human disturbance during migration periods. The probability that a shorebird would flush versus walk or become alert was modeled in response to different disturbance agents during actual disturbance events. Dogs and people had a higher probability of causing shorebirds to flush than vehicles, watercraft, and aircraft. Interestingly, the probability of shorebirds flushing decreased as the agent's group size became larger. Understanding the types of disturbance that most impact shorebirds is critical information when considering multiple potential conservation actions.