Grouping patterns and social organization in Siberian ibex (Capra sibirica): feeding strategy matters

Abstract. A study on group size and composition in Siberian ibex (Capra sibirica) was conducted in the Eastern Tien-Shan Mountains. We found that small groups (1-5 individuals) were most common for this species. Generally, mixed-sex groups were larger than male and female groups. Since males have more ability for fiber digestion, because of their larger body size than females, they are less selective in food quality. Due to this, males gathered into larger single-sex groups in August-September, when forage was at its maximal biomass, and into smaller groups when the amount of food was limited (winter-early-spring). During birthing period, pregnant females typically separated from groups to give birth, returning to the female groups in May-June, when high-quality food was at its maximal availability, making female groups largest in this period. Similar to other sexually dimorphic species, Siberian ibex females and males stayed together in mixed-sex groups during rutting season, demonstrating sexual segregation outside of the rutting season, particularly during summer. Nevertheless, there are still a significant number of males and females that stay in mixed-sex groups throughout the year. In conclusion, the grouping pattern and social organization of Siberian ibex were closely correlated to the availability and quality of their food supply and yearly breeding cycle. Accordingly, Siberian ibexes changed their feeding strategy: being mixed feeders they behaved similar to concentrate selectors when food was scant and preferred small sized groups; while they enlarged their group sizes during seasons when the enriching of forage conditions allowed them to do that. However, group enlarging happened in different months depending on group typology (i.e. mixed-sex, male or female groups) depending on the feeding strategy of their individuals.