Within-group spatial position in Saiga tatarica (Bovidae) in the Stepnoi State Nature Sanctuary, Astrakhan Region, Russia

Abstract

In group-living animals, the social structure and organisation play a significant role in survival and reproduction. Understanding the social aspects of animal lives in the wild may be crucially important for effective conservation of threatened species. The fitness costs and benefits of living in a group are related to particular spatial positions individuals take within their groups. Age and sex of the individual is a major factor determining intra-group spatial position. In the present study, we investigated the within-group spatial positioning of individuals in the Critically Endangered Saiga tatarica (hereinafter – saiga). In saigas living under natural predation pressure in the Stepnoi State Nature Sanctuary (Astrakhan Region, Russia), we investigated the sex-age category of the first individual in the group, the inter-individual distance in the front individuals and the individuals following them, and the distribution of individuals of each sex-age category between various parts of the group. Three (summer) or four (autumn) sex-age categories of the individuals in the moving groups were recognised by direct observations in the field. In summer, adult females, accompanied by their calves, were the very first individuals in most saiga groups observed. This result agrees with the previous notion that experienced females often lead the saiga groups. However, further investigation is needed to confirm whether adult females do indeed take the role of a leader during long-distance group movements. In line with the results on other mammals, the majority of adult females moved in the central third of the group. Spatial preferences of adult females seem to be based on the risk minimisation as the central positions are likely the safest in the group. In autumn, juvenile males were moving first in the majority of the investigated groups probably because they were the most active and fast-moving sex-age category during this season. In addition, juvenile males and females were significantly more often observed in the first third of the group than in the central and the rear thirds. We suggest that despite the fact that the front edge of the group could be the most dangerous spatial position, foraging benefits may outweigh the increased risk for juvenile saigas. In contrast to some other mammals, adult males did not tend to move at the front edge and were equally often observed in the front, central and rear parts of saiga groups. Finally, our results showed that saigas closer to the front edge of the group maintained shorter inter-individual distances than the individuals positioned behind them. The tighter spacing could be used by front individuals to compensate for the increased risks associated with their within-group spatial position.