Imagine a scene of many square kilometres of semi-arid shrubland where an isolated population of 1000 goats is eating the local shrubs. The scene could be interpreted in many ways. In their native environment, or one long-managed for agriculture, the goats may be called indigenous or domestic animals respectively. In other parts of the world the goats may be called pests. What is the difference? It is the effect that the goats have on the shrubland rather than the goats themselves that can be annoying and may necessitate pest control. Hence, some scientific assessment of the effects of the goats is needed.

In a broader context, it is the damage of vertebrate pests that justifies their economic control. It is often the origin (indigenous or exotic) or legal status (declared pest) of a species that is the social justification for control. Non-native species are often labelled as pests without careful assessment of their pest status; are their effects really damage? The differentiation between the impact of a species and the species itself is fundamental to control and to the topics reviewed in this book. This chapter is concerned with estimating the damage of vertebrate pests. Emphasis is on the statistical aspects of design and sampling, with case studies used to illustrate the principles. Finally, there is a review of the analyses used.

For effective pest control it is fundamental to determine the pest status of an animal.