Fallow. The size of the group can give you a good indication; Fallow form large herds, whereas Roe will be solitary, in pairs or occasionally trios. Muntjac and CWD are also fairly solitary, although occasionally you will have many pairs/individuals feeding in the same area giving the appearance of a group. Red will form large herds on Scottish hillsides and areas where they are present in large numbers, but those are limited parts of the country. Sika I have never stalked so I do not know!