Rabbits (Oryctolagus cuniculus) and deer (red (Cervus elaphus) and roe (Capreolus capreolus)) are the most common wild herbivores in the United Kingdom where they have a considerable effect on vegetation structure and on plant diversity over very large areas of both grassland and woodland. There are several examples of ecosystems in which these animals are the principal determinants of plant composition and structure, and therefore of habitat for other organisms. Whilst it is important to know whether numbers of either or both of these herbivores have changed appreciably, there are no practicable methods of making direct measures of their population size, and an index method based on dropping counts is therefore used to estimate relative abundance. The recording method is expected to detect changes similar to those which have occurred in the past, such as the dramatic fall and slow recovery of rabbit numbers following the introduction of myxomatosis.