Can electrical wires serve as canopy bridges? A case study of the dusky langur (Trachypithecus obscurus) in Thailand

Abstract

In many parts of the world, primates and other arboreal and semi-arboreal species use electrical and telecommunication cables to cross open gaps. However, electrocutions can occur when the cables are uninsulated or damaged. Between 2001 and 2002, during a 12-month behavioural study of two dusky langur groups (Trachypithecus obscurus) at the Royal Thai Air Force Base in Prachuap Khiri Khan Province, peninsular Thailand, we recorded langur use of and mortality on electrical and telecommunications cables on an ad libitum basis. Before insulation of the cables in late 2001, five langurs died by electrocution; post insulation, that number decreased to only one case on March 5, 2002. In 2022, we returned to observe the langur groups and saw them continuing to use the cables for crossing and noted damage to the insulation, indicating the importance of maintenance. Electrical cables can provide canopy connectivity for langurs and prevent dangerous encounters with dogs on the ground, but cables must be insulated and inspected regularly. As additional mitigation measures, we suggest providing alternative substrates for travel such as planting more native trees and providing artificial canopy bridges.