Between-season differences in habitat use by Black Grouse Tetrao tetrix were studied on four moors in the northern Pennines between 1989 and 1992. Heather moor and bogs were preferred at all times of the year, apart from during the breeding season. In spring, large quantities of Cotton-grass Eriophorum vaginatum flowers were consumed, whereas in autumn and winter Heather Calluna vulgaris was more important. Enclosed fields on the edge of the moors were regularly used in autumn and winter by large flocks of cock birds, and hens were found in smaller groups. Where present, overgrazed grass moorland was generally avoided, apart from during the summer. Similarly, enclosed rough grazing allotments rich in rushes were favoured during the summer months by breeding hens and moulting cocks.