A test for measuring individual variation in how far grazing animals will move away from a social group to feed

This paper describes a test for gregarious grazing animals, which measures trade-offs between feeding and social companionship. Four groups of 10 female Scottish Blackface sheep were used for the study and bowls containing food pellets were used to draw individuals away from the group. The sheep were individually observed four times (once every 2 weeks) for 30 min each in a 65 m x 33 m grass arena, while the rest of the group were confined at one end. The first time was a control test (C) with no food bowls. Other three times were pellet tests (P1-P3), with 12 bowls placed at 5-m intervals along the length of the arena and 25 g food pellets in each bowl. In addition, within-group sociability indices (SIs) were measured while the sheep grazed together during the weeks without tests. Both the maximum and average distance from the group were higher in P1-P3 than in C. The maximum distance increased between PI and P3, with only three animals failing to reach the furthest bowl in P3, although average distance from the group did not change between runs. The time taken to visit all the bowls for the first time decreased between P I and P3, although the total number of bowl visits increased. There were positive correlations between runs in average distance from the group and the total number of bowl visits. In each group, the five sheep with the highest S1 values had lower maximum and average distances, tended to take longer to visit the bowls for the first time in P1 and were more vigilant than the rest of the group. It is concluded that the test can detect differences in the willingness of individuals to move away from a social group and could be used to compare different species or breeds of animal, as well as individuals within species, or to compare the attractiveness of different social companions. (c) 2005 Elsevier B.V. All rights reserved.