Socio-ecology of phayre's leaf monkeys (Trachypithecus phayrei) at Phu Khieo widlife Sanctuary

We report first results from our ongoing study of phayre's leaf monkeys (Trachypithecus phayrei) on the social structure, feeding, and ranging behavior. The study site is located at Phu Khieo Wildlife Sanctuary, Chaiyaphum Province, Northeast Thailand harboring four macaque and two leaf monkey species as well as white-handed gibbons and slow loris. In October 2000, we began with the help of sanctuary rangers and research assistants to establish a trail system and to habituate leaf monkeys. It took about one year to habituate each of three focal groups. During contacts with these groups we collect information on group composition and every 30 minutes on the activity of individuals (via scan sampling) and location (via GPS). Groups are composed of one to several adult males, ca. seven adult females on average plus immature individuals (average 16.3 individuals). Dispersal is female biased with ca. 1.0 female immigrations per group-year. These results match rather closely findings for other populations and the genus in general. However, social relationships deviate from expectations such that the supposedly unrelated females have frequent affiliative contacts, have decided dominance relationships and linear hierarchies. Males appear to be more affiliative than males of other species, because they frequently associate and occasionally care for infants. More insights into the social structure could be gained from analysis of genetic relationships of individuals within groups. Activity and ranging follow the expectations for a leaf-eating monkey. Inactive and feeding are the predominating activity and the diet is mainly composed of leaves. However, unexpectedly fruits form a rather large part of the diet and the largest groups was feeding longer and was less inactive indicating indirect competition for food. Home range sizes are comparatively large and day ranges long. We conclude that phayre's leaf monkeys live at rather low densities and seem to incur some cost by living in larger groups switching to lower quality food. Overall it appears that the habitat at Phu khieo WS does support a high biodiversity of primates, but cannot carry high density populations possibly related to seasonal bottlenecks or interspecies competition.