Landscape approaches to studying the effects of disturbance on waterbirds

The internationally important populations of waterbirds that winter in the United Kingdom can face intense pressure from human disturbance as a result of the high urbanization found around many protected coastal or inland wetland sites. Here, I describe and evaluate an approach that has been used to investigate the spatial effects of human disturbance on waterbirds. Rather than directly investigating behavioural responses to individual disturbance events, the presence of features in the landscape associated with disturbance is instead used as a surrogate, with the essential aim being to demonstrate that bird numbers or densities are depressed or their behaviour altered in proximity to areas used by humans. This paper first describes case studies that demonstrate the limitations of the basic inference (i.e. that disturbance influences patterns of waterbird distribution or behaviour) and then how investigations might be strengthened. For conclusions to be sound, it is particularly important that other factors, such as food supply, that might also explain the spatial patterns observed are considered or other corroborative evidence presented. The approach is thus least applicable in the most heterogeneous environments where many factors, perhaps spatially autocorrelated, may explain variation in distribution or behaviour. However, greatest confidence in the validity of conclusions may be gained where studies are able to show (ideally by experimental manipulation) that species' distributions or behaviour vary temporally in line with the levels of human use of the features examined. Although its aim and scope are thus limited, the use of a landscape approach, provided that it takes into account other factors affecting spatial variation in bird abundance or behaviour, can provide a preliminary assessment of species avoidance of key sources of disturbance that may offer a framework for more detailed investigation.