Mali, who lives at Paignton Zoo Environmental Park in Devon, balanced effortlessly like a tightrope walker on the line, which is about 20 feet off the ground.

Mali (20) and her two-year-old toddler Tatau had been climbing around in a cargo net on one of their islands. Then Tatau decided to go off and do a bit of exploring by herself. Mali, who is described as an excellent mother, then walked the tightrope to a spot where she could stop and look down at her youngster.

Zoo spokesperson Phil Knowling said: “She seemed to balance quite effortlessly, using her long arms like an acrobat uses a pole. It was a quite amazing bit of skill. You can’t imagine many humans doing that!

“Upright walking on thin branches is very important for orang utans, as they need to get to the outer edges of tree crowns where fruit is found. Walking on four legs is very difficult on a thin branch, especially one that is bendy and moves beneath you.”

The Bornean orang utan (Pongo pygmaeus) is threatened by hunting, the pet trade and the destruction of its rainforest habitat. Forest is being destroyed to create commercial plantations to grow palm oil and other products. Given the declining populations, measures such as switching to alternative oil products and maintaining sustainable populations of orangs in zoos are becoming ever more important.

Paignton Zoo and sister zoo Living Coasts are working to become palm-oil free sites. Curator of Mammals Neil Bemment is vice-coordinator of the orang-utan European Endangered species Programme, which coordinates the efforts of top European zoos to conserve the species.

The Bornean orang utan is classed as Endangered by the IUCN Red List, which is the world's most comprehensive inventory of the global conservation status of plant and animal species. A species is Endangered when the best available evidence indicates that it facing a very high risk of extinction in the wild.

In addition to Mali and Tatau, Paignton Zoo’s group of Bornean orang-utans includes females Gambira, Chinta and her baby Natalia. Paignton Zoo Environmental Park is a registered charity. For more information go to www.paigntonzoo.org.uk or ring 0844 474 2222.