It's hard for humans to tell what wild yaks are doing up there. Living high in the Tibetan Plateau, the rare ungulates are not easy to find. When scientists managed to track some down, they saw that females are hanging out in huge groups with no males allowed. And, though no one knows why, the females prefer habitat that's higher and steeper than where the boys play. Currently rebounding from poaching, wild yaks—which, male and female, look a bit like bison wearing skirts—are still endangered. Yet without knowing much about where or how yaks live, conservationists can't be sure of the best ways to protect them. So University of Montana biologist Joel Berger and his colleagues traveled to Tibet in late 2012 and went looking for yaks. The researchers crisscrossed the Kekexili National Nature Reserve, a protected area of the Tibetan Plateau with an altitude ranging from 4,300 to 6,900 meters (4.3 miles). They drove nearly 1,100 kilometers on dirt roads or worse, watching for yaks nearby or in the distance. Whenever they spotted a group of the animals they made note of whether it included males or females, whether there were calves, what they were doing, and what kind of terrain they were on. To get more details, they left their vehicles and approached on foot—"with stealth," the authors note. "The males are fearless," Berger says. "I have always been timid because with little vegetation and no trees, if a yak gets annoyed, then you have a real problem." Nevertheless they managed to gather data for 108 groups of yaks. Some stark differences between the sexes emerged. Male yaks were usually on their own or in groups of two or three. But females hung out in groups of more than 30 on average. The largest female group had over 200 animals. Berger says this pattern of sex segregation is common for big grazers. "We find larger female than male groups in many species, from elk to bighorns," he says. Presumably, this provides safety in numbers, so that females can protect their young against predators. "More eyes, noses, etc.," Berger says. Analyzing the favorite habitats of male and female yaks revealed more differences. Female groups were found at slightly higher elevations than males. And while males tended to hang out on the flatter plains, females preferred slopes and hills—the steeper, "more precipitous" terrain, the authors write. This was especially true if the groups had calves with them. Part of the reason females prefer rugged terrain may be protecting their young from wolves. The authors witnessed three interactions between yaks and wolves, all occurring on flatter ground. But this probably isn't the whole story. In general, "Wolves do just fine on steep slopes," Berger says. The hilly habitats may give females better access to meadows with more food and water, so they can feed both themselves and their young. Males, which don't have calves to worry about, stick to the easier terrain. So do females take on some risk or difficulty by living on the steeper slopes? "[We're] just not sure," Berger says. "We know so little about yaks." Even though yaks are still largely a mystery, any new information about the animals will help conservationists do their work. "At this point, we're just getting grounded in terms of understanding yak ecology," Berger says. "Knowing more about how females and males vary is a small, small step." Someday he hopes conservationists will know enough about the animals to understand how the movements of herders on the plateau, or the introduction of new mining operations, might affect them. For now, Berger is optimistic. "Yaks are making a comeback," he says. Knowing what females are doing in their club meetings will have to wait, though it's probably driving the male yaks crazy too. Image: J. Berger, Wildlife Conservation Society
JOEL BERGER, ELLEN CHENG, AILI KANG, MICHAEL KREBS, LISHU LI, ZHAO XIN LU, BUQIONG, BUZHOU, & GEORGE B. SCHALLER (2014). Sex differences in ecology of wild yaks at high elevation in the Kekexili Reserve, Tibetan Qinghai Plateau, China. Journal of Mammalogy : 10.1644/13-MAMM-A-154
NOTE: This paper appears not to be online yet, but I'll add the link as soon as it's available.