Dynamics of grouping patterns and social segregation in feral goats (Capra hircus) on the Isle of Rum, NW Scotland

We investigated group size, grouping patterns and sexual segregation in feral goats on the Isle of Rum (NW Scotland) from January 1981 to September 1982 and May to November 2000. A total of 7396 groups of feral goats were recorded, comprising 30356 adult individuals and 13119 yearlings and kids. The most commonly observed group size was 1-3 individuals. Mean group size was larger in 2000 than in 1981-82, possibly reflecting an increase in population size. In both study periods, group size varied throughout the year: mean group size was smallest in late winter and early spring, and increased through summer to reach a maximum during the August/September rutting period. Mixed-sex groups were larger than single sex groups. Feral goats on Rum showed obvious social segregation during late spring and summer months (April to July) as demonstrated by a lower percentage of mixed-sex groups, lower proportions of adult males and females observed in mixed-sex groups and a higher social segregation coefficient in these months. The extent to which the population became sexually segregated correlated most strongly with daylength. This probably reflects the goats' pattern of habitat use during foraging: large mixed sex parties, which use caves for overnight shelter, forage slowly up the hill sides during the day, gradually dispersing more widely as they go. In winter months, when days are short, the animals are able to move less far, and so become less dispersed. © Publications Scientifiques du Muséum national d'Histoire naturelle.