Differential reactions to anthropogenic disturbance by two ground-nesting shorebirds

Many ground-nesting shorebirds experience a high level of anthropogenic disturbance, often to the detriment of their breeding success. This study investigated the responses of the Near-Threatened African Black Oystercatcher Haematopus moquini (ABO) and the Least Concern Kelp Gull Larus dominicanus vetula (KG) to anthropogenic disturbance during the pre-breeding and breeding season at three locations differing in levels of anthropogenic disturbance and colony size. Birds were directly approached from over 100 m away and markers were dropped at each behavioural reaction to the approach. Measuring back allowed a quantitative measure of the effects of disturbance. Stand response distances in breeding ABO were location sensitive, which related to disturbance level, showing that they stood up earlier in a highly disturbed location. Neither ambient conditions (wind speed and ambient temperature) nor nesting condition (egg age and clutch size) played a significant role in responses. Interestingly, breeding KG behaviour was affected by location, to a lesser extent by clutch size, but not by ambient conditions. Both ABO and KG significantly altered their behavioural responses to disturbance from pre-breeding to breeding. These results emphasise the need to have a buffer zone surrounding breeding areas excluding human presence to allow for the successful breeding of ABO.