Antipredation Sleeping Behavior of Skywalker Hoolock Gibbons (Hoolock tianxing) in Mt. Gaoligong, Yunnan, China

Studying sleeping behavior can provide key information for understanding the ecology of a species. Antipredation is an important factor that affects primate sleeping behavior. We studied antipredation sleeping behavior in skywalker hoolock gibbons (Hoolock tianxing). We studied one group (NA) and a solitary female (NB) at Nankang from July 2010 to September 2011, and another group (BB) at Banchang from May 2013 to December 2014 in Mt. Gaoligong, Yunnan, China. Over the study period, we recorded 67 sleeping trees for members of group NA over 92 days, 17 trees for the solitary female NB over 22 days, and 159 trees for members of group BB over 186 days. Skywalker hoolock gibbons at both sites rarely used the same tree on consecutive days (N = 3 at both sites). They traveled fast to enter sleeping tree a mean of 160 +/- SD 43 min before sunset at Nankang, and a mean of 192 +/- SD 40 min before sunset at Banchang. They seldom (Nankang: 14%, N = 183 observations; Banchang: 25%, N = 548 observations) defecated in sleeping trees. They slept at sites with more tall and large trees and preferred to sleep on tall trees in the site. They slept on branches of small diameter and closer to tree tops. Our study suggests that antipredation plays an important role in skywalker hoolock gibbons' sleeping tree selection and sleeping behavior. In addition, our data suggest potential effects of habitat degradation on gibbons' sleeping behavior. Tall trees are especially important for gibbons in degraded forest and should be protected.