Nonrandom mixing between groups of Przewalski's gazelle and Tibetan gazelle

Abstract

Przewalski’s gazelle (Procapra przewalskii) and the Tibetan gazelle (P. picticaudata) are endemic, closely related, and endangered ungulates of the Qinghai-Tibetan Plateau. The 2 species often occur in mixed-species groups in the upper Buha River of the Plateau. We studied the composition and size of their mixed-species groups over 2 years to determine whether such groups aggregate by chance and to determine a posteriori potential costs and benefits associated with the formation of mixed-species groups. Sex composition and size distribution were similar in single-species groups for both species. Given that population density also was similar for these species, we expected that mixed-species groups that formed by chance would consist of an equal mix of the 2 species. This was true in male and in mixed-sex groups; however, the proportion of female groups composed of Przewalski’s gazelles was much larger than expected. In addition, mixed-species groups in winter never included males of both species. The results suggest that these 2 gazelle species do not associate randomly. Mixed-species groups were larger than single-species all-female, all-male, and mixed-sex groups, suggesting that individuals in larger groups may benefit from a reduction in predation risk. The occurrence of mixed-sex, mixed-species groups may increase the risk of crossbreeding and represent a cost to the formation of mixed-species groups in these two gazelle species. DOI: 10.1644/09-MAMM-A-203.1.