The seasonal diet of adult black grouse Tetrao tetrix was studied from 1988 to 1991 within a 17 km? area of the Pennine uplands of northern England. Diet was assessed through faecal analysis of samples collected from radio-marked and flushed birds, from lek sites where males displayed throughout the year, and from broods of six radio-marked females. The diet of adults consisted of leaves, flowers, fruits, and seeds from a large number of plant species. In autumn and winter, leaves and stems of Calluna vulgaris formed the major part of the diet of both sexes. In winter, cocks consumed a greater proportion of heather than hens. Leafy material from herbs and grasses formed the remainder of the autumn and winter diet. In early spring, shoots of Eriophorum vaginatum provided a valuable early protein source for both cocks and hens. In spring and summer, leaves, flowers, fruits, and seeds of grassland and moorland ericaceous shrubs, herbs, grasses, sedges, and rushes were taken as they became seasonally available within the birds' range. Tree food rarely occurred in the diet, but was eaten by some individuals in autumn, winter, and spring where it was available. Tentative comparisons with the diet of cocks from other north English moorlands showed similarities in plants eaten, but their proportions often varied widely. The invertebrate diet of young chicks in these moorland habitats was particularly rich in sawfly larvae; Lepidopteran larvae, beetles, dipteran flies, and parasitoid wasps, although less abundant in the diet than sawfly larvae, were also important dietary constituents. Ants which are common in black grouse chick diets in forested habitats, were rarely found in chick faecal material.

Key words: black grouse, moorland, northern England, seasonal diet, Tetrao tetrix

Anne E. Westerberg, 32 Manor Road, Medomsley, Consett, Co. Durham, DH8 6QW, United Kingdom