How do free-ranging domestic herbivores reduce competition within owner-determined herds?

Abstract

Group size and competition are key drivers of foraging behaviour in social animals. With seasonal changes in food quality and availability, comes changes in the type (scramble or interference) and degree of competition (aggression or none). One way that animals can deal with these variations is by living in groups where the benefits of the group size outweigh the costs. However, this is generally not possible with domesticated animals, as group sizes are determined by owners. Thus, within these groups, animals have to make behavioural adjustments to reduce competition. To determine how domestic indigenous veld goats (Capra hircus), living in different sized owner-determined groups, dealt with seasonal variations in food availability and quality, and thus competition, we recorded their foraging behaviour. Specifically, we documented patch-joining events, herd splits, and interindividual distances (IID). We found that goats only joined the patches of other herd members during the wet season, when food was more readily available. In addition, we found that large herds split into a number of smaller subherds (comprising ca. 15 individuals) that were similar in size to the unsplit small herds. Furthermore, these splits primarily happened during the dry season and were more frequent in large herds compared to small herds. Finally, IID increased in the dry season for both small and large herds, likely as a way to reduce interactions while feeding. Yet, individuals in large herds maintained larger IID than individuals in small herds, suggesting a greater attempt to reduce interactions in large herds. The fact that the large owner-determined herds had to elicit a greater number of behaviours, suggests greater levels of competition in these herds in the arid savanna system. These results suggest that by using behavioural indicators such as IID or herd splits, owners could monitor competition within their herds and determine when it would be better to keep their goats in smaller herd sizes.