The diet of weasels, Mustela nivalis and stoats, Mustela erminea during early summer, in relation to predation on gamebirds.
Gamekeepers usually trap weasels (Mustela nivalis) and stoats (Mustela erminea), since they consider that these and other predators can adversely affect the production of gamebirds (Galliformes). Although very little work has been done on this aspect of predation, some ecologists consider that predators have no significant effect on the size of gamebird populations (e.g. Jenkins, Watson & Miller, 1964).
However, Potts & Vickerman (1974) gave data which suggested that some predators, such as weasels and stoats, may significantly reduce the survival of gamebird chicks.
Day (1968) made a detailed study of diet of these mustelids, using material collected from 27 estates in Britain, and found no significant seasonal differences. However, he had insufficient data from the early summer (May and June), when fewer Mustelidae are caught compared with later in the year (Jefferies & Pendlebury, 1968). As gamebird chicks are only present during the summer, the results given here mainly concern stoats and weasels killed during May, June, and July.
The study area, situated on the South Downs in West Sussex, is hilly and used for arable farming; there are few woods and land that is not cultivated is mostly grass or scrub. Closely grazed downland now occurs in only one or two places. Further details of the study area and the population dynamics of partridges can be found in Potts & Vickerman (1974).