Impact of human disturbance on coastal birds: population consequences derived from behavioural responses.

Abstract

Disturbance of wildlife is inevitable in a world with a rapidly increasing human population. Whilst improving engagement with the natural world can have the benefit of encouraging people to help protect it, there is also the issue of increased potential for damaging effects of disturbance. A better understanding is needed of the circumstances under which disturbance would be expected to be a conservation problem, either alone or in combination with the impacts of other human activities. The aim of this thesis is therefore to address these questions: using wintering waders in estuarine habitats as the study system and taking a joint fieldwork and simulation modelling approach. Fieldwork was centred on Poole Harbour; an estuary and wetland of international importance located on the south coast of the UK. Disturbance experiments and observations showed that bird responses to disturbance are highly variable and related to factors including body mass, environmental conditions, site quality, and disturbance type. The energetic and lost-feeding-opportunity costs of responding to individual disturbance events were relatively small and therefore considered unlikely to cause major reductions in individual body condition or significantly limit overwintering population size, given observations of present-day spatial and temporal patterns of human activities. Simulation modelling using two types of individual-based model (IBM) supported this conclusion. Although high levels of disturbance can have a significant impact on wintering bird populations, current frequencies of human activities in Poole Harbour were not found to be reducing the carrying capacity of the site. Increased disturbance frequencies were predicted to be problematic, however, in combination with environmental change that reduced bird ability to meet their daily energy requirements: such as loss of foraging habitat through sea level rise, or reductions in prey availability due to over-exploitation. This has important implications for identifying the most effective conservation management methods. As well as site-specific management recommendations, this research contributes to understanding of the mechanisms by which disturbance may or may not have a significant impact on wintering wader populations; along with applications to other systems; and tools and general principles that conservation managers and decision makers can use to prioritise further investigation and action.