An analysis of factors influencing spatial distribution in flocks of grazing sheep

The spatial distribution of small groups of sheep (5–40) when grazing at a range of densities (4–29 sheep ha^?1) was investigated experimentally. Under these conditions, where the sheep groups rarely split into distinct sub-groups, the angular distributions of the sheep were usually random, but the radial distributions were not. A “concentration curve” representing the density of the sheep as a function of their distance from the centroid of the flock exhibited a peak at a distance varying with breed, flock size and density. Dorset Horn sheep were distributed more widely than Merino, Polwarth, Corriedale or Southdown sheep. Distribution, also measured as area “occupied” per sheep, ranged from 15 to 67 m² among these breeds.Two breeds were studied in detail. Both Merino and Corriedale sheep spread further apart as flock size increased. As density decreased, Merinos but not Corriedales came closer together. There was little correlation in these studies between area occupied per sheep and distance to first nearest neighbour, because distance to nearest neighbour varied relatively little compared with that of average area occupied. Thus, spatial dispersion seems to have two components: (a) a relationship to a neighbour by each individual; (b) spatial cohesion of the group as a whole which is influenced by group size and density.