【行動】オランウータンが樹上から降りてきた理由

Orang-utans may venture down from their arboreal habitat in the Bornean rainforest more often than previous anecdotal observations indicated. Research published in the journal Scientific Reports provides evidence of male and female orang-utans of all ages travelling on the ground. The study suggests that orang-utans may potentially be more resilient to drastic habitat change than previously thought.

The Bornean orang-utan (Pongo pygmaeus) is the world’s largest arboreal mammal. Records of terrestrial behaviour are rare and tend to be associated with habitat disturbance. Marc Ancrenaz and colleagues conducted a large-scale analysis of orang-utan terrestriality using comprehensive camera-trapping data from 16 sites across Borneo. The authors sought to evaluate the extent to which orang-utans come down from the trees to travel terrestrially, and the whether anthropogenic disturbances influence this behaviour.

Orang-utans from all age-sex classes were recorded on the ground, with large flanged males (those with distinctive cheek pads, throat pouches and long fur) making terrestrial appearances most frequently. Additionally, orang-utans were recorded on the ground in primary forests as well as in heavily degraded habitats, suggesting that anthropogenic canopy disruptions may influence terrestrial activity, but are not the only driver of this behaviour. The findings suggest that terrestrial locomotion may have a larger than expected role in the Bornean orang-utan’s natural behavioural repertoire.