Sexual/aggressive behavior of wild yak (Bos mutus Prejevalsky 1883) during the rut: influence of female choice

Abstract

Wild yaks (Bos mutus) ranged across the Tibetan Plateau in large herds before being forced to remote areas of the plateau. Consequently, little has been published about their behavioral ecology. We present the first extensive study on wild yak behavior during the rut. We gathered data on activity budgets, aggressive/sexual behaviors, and the behavior of bulls inside and outside mixed groups during 11 days in 2010 and 9 days in 2011. Yaks ate less and were more social during the rut than during summer. Males ate less than females and socialized more during the rut. We observed yaks for 234.25 h and recorded 2,078 aggressive/sexual behaviors. Yak bulls inspected and tended cows showing off their profiles during lateral displays, the most common type of indirect aggression. Yak bulls inside mixed sex groups rested less and socialized more than bulls outside. Females initiated intense intra-sexual competition and led at least 25 bulls on chases. Females then incited fight frenzies of numerous bulls from inside and outside the groups before copulations, and fights could be intense. We discuss female choice selecting for large size and fighting ability in males, the similarity of yak and bison (genus Bison) behavior, and conservation implications.