The impact of geophagy on ranging behaviour in Phayre's leaf monkeys (Trachypithecus phayrei)

Resource use is known to influence the ranging behaviour of primates, and this effect may be pronounced when the resource is uncommon in the environment. Here we investigate the effect of geophagy on the ranging behaviour of Phayre's leaf monkeys (Trachypithecus phayrei) in the Phu Khieo Wildlife Sanctuary, Thailand. UTM coordinates were collected via GPS from the group centre every 30 min during all-day follows of one study group over a 4-month period. On days during which the group visited a distant saltlick (n = 3), the monkeys travelled significantly further (p < 0.001), significantly faster (p < 0.001) and with fewer stops compared to non-saltlick days (n = 61). Saltlick visits also increased the home range size from 73.7 ha to 93.4 ha. Increased daily path length, increased travel speed and consistent pace are necessary because of the distance from the saltlick to the regularly used portion of the home range, and these reflect the import- ance of soil consumption to the leaf monkeys.