Diet selection and activities of sheep and red deer grazing alone and together across a grass (primarily Lolium perenne/Agrostis capillaris) and heather (Calluna vulgaris) boundary, between July and October, are described.

Throughout the experiment, both animal species had a much higher proportion of grass than heather in their diet. Time spent grazing on each type of vegetation was similarly greater on grass, and the bite rates of the animals were also more rapid on the grass than on the heather.

Red deer spent more time grazing per 24 hours than did sheep, with sheep grazing less during darkness hours than red deer. Total grazing time of both species did not decrease with decreasing daylength from July to October.

There were no consistent differences in the diurnal patterns of activity of sheep and red deer, with both species showing 2-3 large grazing peaks per day.

There were no consistent effects of mixing sheep and deer on their grazing behaviour and diet composition.