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BiologyVery little is known about these elusive monkeys, and the first comprehensive study of their ecology and behaviour only took place in the 1990s (5). Unusually for langur monkeys (which normally feed on leaves), the diet of the Yunnan snub-nosed monkey is composed primarily of lichens, such as those of the genus Bryotia (7). Lichen is an abundant and easy to digest food source but it is relatively poor nutritionally; this unusual diet has led to other aspects of behaviour that are unique amongst tree-dwelling primates (5). For example, large groups of up to 300 individuals have been observed (5), probably as a result of low food competition between members (7). These troops appear to be made up of small family groups consisting of an adult male, three to five females and their offspring (5), although the whole troop will tend to travel and rest together (7). Reliance on lichen, which can take between 10 to 15 years to regenerate, has also caused these monkeys to have a more wandering way of life (5). A troop will cover around 1,500 metres in one day and their home range reaches as much as 25 square kilometres (7). The birth rate is also low for this species; scientists estimate that a female gives birth about once every three years (5).