The effects of human disturbance on breeding and foraging birds
The appropriate management of visitors to nature reserves is an important conservation concern. In this thesis I briefly review the current literature describing the effects of disturbance on wildlife, concentrating mainly on birds (Chapter 1). Recent literature has provided worrying critiques of the practical and theoretical bases upon which management practice is based. Here, I address a number of questions that seek to clarify the impacts of human disturbance on birds. I started by asking whether behavioural measures of disturbance are accurate indices of the negative effects of disturbance. Through an experimental test of a theoretical model, I showed that animals that respond most to disturbance may in fact be those individuals that face the lowest cost associated with such disturbance (Chapter 2). Turnstones Arenaria interpres provided with extra food over three days showed stronger behavioural responses to a standardised disturbance stimulus than those without extra food. Behavioural measures are therefore not always a good index of disturbance effects. Consequently, the conclusions of some of the studies reviewed in Chapter 1 must be considered doubtful. Although some large declines in breeding success of some species are caused by human disturbance, such effects are obvious, simple to remedy and appear to be rather rare. If human disturbance is a general concern it is therefore necessary to assess whether human disturbance has impacts on species that are not obviously sensitive. To investigate this, I modelled the impact of human disturbance on the nesting success of kittiwakes Rissa tridactyla and guillemots Uria aalge (Chapter 3). By directly measuring a range of nest site parameters as well as those parameters involving human disturbance, I was able to improve the power of the analysis to detect disturbance effects over those of previous, less detailed, studies.