Sleeping site use of the white-headed langur Trachypithecus leucocephalus： The role of predation risk, territorial defense, and proximity to feeding sites

We collected data on sleeping site use from two groups of white-headed langurs Trachypithecus leucocephalus living in Fusui Nature Reserve, China between August 2007 and July 2008. This information was used to test several hypotheses regarding ultimate causes of sleeping site use in this primate. White-headed langurs slept either in caves （17 sites） or on a cliffledge （one site）. They used all sleeping sites repeatedly, and reused some of them on consecutive nights; three nights was the longest consecutive use of any one sleep site. We suggest that langurs use sleeping sites to make approach and attack by predators difficult, and to increase their own familiarity with a location so as to improve chances for escape. Langurs＇ cryptic behaviors with an increased level of vigilance before entering sleeping sites may also help in decreasing the possibility of detection by predators. Group 1 spent more sleeping nights in the central area of their territory than expected; in contrast, group 2 spent more sleeping nights in the periphery of their territory, which overlaps with that of another groups, than expected. The position of sleeping site relative to the last feeding site of the day and the first feeding site of the subsequent morning indicated a strategy closer to that of a multiple central place forager than of a central place forager. These results suggest that territory defense and food access may play an important role in sleeping site use of white-headed langurs [Current Zoology 57 （3）： 260-268, 2011].

Male attacks on infants and infant death during male takeovers in wild white-headed langurs(Trachypithecus leucocephalus)

Infanticide was first observed in langurs nearly 50 years ago,and this rare phenomenon has been inferred to have either an evolutionarily adaptive function or to be a pathological and non-functional behavior.In this study,we report 5 male takeover events in one-male groups of white-headed langurs in the Nongguan Karst Hills,Guangxi,China from 1998 to 2006.We recorded 13 attacks on 9 infants by extra-group males or new resident males.During the male takeovers,all of the infants younger than 6 months(with an average age of 3.6 months[N=11])in the groups disappeared.The infant death rate during the 4.2 months after takeover by a new male was significantly higher than the infant death rate calculated for most of the year.Older infants that were still nursing(with an average age of 14.1 months[N=7])were often attacked and seriously wounded by the extra-group males or new resident males,but all of them survived.The interbirth intervals of females whose infants were assumed to be killed by males were significantly reduced relative to those of females in groups with stable male tenure(mean=10 months vs 25 months).Our data suggest that males kill unrelated and unweaned infants during the takeover period to decrease the time until the infants’mothers resume fertility.Thus,infanticide would support sexual selection theory in white-headed langurs.The data also show that infanticidal behavior was directed toward the infants,especially those who were still nursing.Female dispersal may function as a counter-strategy to avoid infanticide.

Genetic analysis of group composition and relatedness in white-headed langurs

We collected fecal samples of white-headed langurs from 3 of the 4 remaining habitat fragments(Fa,Fb and CZ)located in southwestern Guangxi,China in Nov 2005,and used 5 microsatellite loci and the SRY gene to assess the relatedness between 46 langurs within and between groups.We observed 2 forms of group structure:one-male/multi-female groups(OMGs)and all-male groups(AMGs).One AMG in Fa was composed of 2 generations,included a father,2 sons and 1 unrelated male,and all OMGs in all 3 habitats included 1 resident male,several adult females and offspring.Of the 21 identified father-offspring cases,the resident male fathered 20(95%)and the non-resident male sired 1(5%),suggesting that adult males had overwhelming priority of access to females as the resident male in an OMG,while the non-resident male may also have the opportunity to adopt surreptitious mating strategies.