Associations between individuals and home-range behaviour in natural flocks of three breeds of domestic sheep

Abstract

The associations formed between individual sheep in natural flocks of Dorset Horn, Merino and Southdown sheep were studied. In these flocks, the sexes were not separated and little culling was carried out; breeding occurred naturally. The locations of individuals were mapped when the sheep were grazing and when they were camped. The breeds differed in their tendency to disperse. Merinos rarely formed sub-groups, Southdowns usually formed a few sub-groups and Dorset Horns always formed many sub-groups. All Dorset Horn and Merino sheep of both sexes formed associations with other sheep at some time. Associations, which varied in frequency, were relatively short-lived, being present for one three-week study-period but not often being present three months later. When an association involved two sheep, the animals were relatives only on 22% of occasions, but in larger associations, two or more related animals were present in 50% of Dorset Horn and 36% of Merino associations. The association in Merinos meant that animals grazed close to one another in the flock since no sub-groups were formed. Single linkage cluster analysis, principal coordinate analysis and the technique of Grassia (1978) were used to compare the general propensity of Southdown and Dorset Horn sheep to form associations. The Southdowns formed very close associations when grazing but not when camping, whereas the Dorset Horns formed less close associations but did so during both grazing and camping. In both breeds, the associations were mostly between sheep of similar age and sex, with males > 2 years old forming the strongest associations and keeping apart from the older females; these females also tended to associate together. When the Dorset Horns were grazing, the associations between individuals were within “feeding” home ranges. In the Southdowns, the individuals associating together used widely dispersed areas of the paddock, rather than one general area. Merinos dispersed into sub-groups only under extreme food shortage and then the sex and age groups segregated as in the other two breeds. Thus, there appears to be a wide variation between these breeds of sheep in their social organisation.