INTRODUCTION

Accurate and up-to-date distribution maps and a good numerical insight into population sizes and trends are a prerequisite for effective conservation. The conservation status of a species hinges on three questions: ‘Where are they?’, ‘How many are there?’ and ‘What is their trend?’ This chapter focuses on providing answers to these questions. We cannot conserve what we do not understand.

This chapter provides a series of examples and case studies into conservation applications of bird inventories and bird monitoring. However, even the best inventories and perfect monitoring make no contribution to conservation on their own. This information simply allows an assessment of the status of a species or a site: it will not, for example, halt a species' decline. Explanations need to be found for trends, and management and action plans need to be compiled and implemented. Monitoring needs to be built into these actions, otherwise we have no measure of the impact of conservation interventions.

One of the most outstanding conservation successes of the twentieth century – the widespread removal of organochlorine insecticides from the environment – showed clearly the role that monitoring plays in bird conservation. These harmful chemicals caused direct mortality of adult birds of prey, most notably peregrines (Falco peregrinus), through accumulation in body tissues, and caused indirect mortality through thinning of their eggshells leading to reduced hatching success and poorer breeding performance. Consequently, peregrine populations declined worldwide, and only recovered when organochlorine usage was reduced.