The white-headed langur (Trachypithecus poliocephalus) is a critically endangered langur from Cát Bà Island, Vietnam (T. p. poliocephalus), and Guangxi, China (T. p. leucocephalus). Both taxa are overall blackish, but the crown, cheeks and neck are yellowish in T. p. poliocephalus, while they, as suggested by its scientific name, are white in T. p. leucocephalus. As all members of the Trachypithecus francoisi species group, this social, diurnal lutung is found in limestone forests.
The nominate subspecies, often known as the golden-headed or Cat Ba langur, is among the rarest primates in the world, and possibly the rarest primate in Asia. The taxonomic position of the Chinese population, while also highly endangered, is more confusing. It has been considered a partially albinistic population of the François' langur (T. francoisi), a subspecies of Francois' langur, a valid species (T. leucocephalus), or a subspecies, T. poliocephalus leucocephalus. Comparably, poliocephalus was considered a subspecies of Francois' langur until 1995.
According to the Cat Ba Langur Conservation Project, the The Cat Ba langur's skin is black and the pelage color is dark brown; head and shoulder are bright golden to yellowish-white. The tail is very long (ca. 85 cm) compared to the body size (ca. 50 cm). Babies are colored golden-orange; the pelage starts to change its color from about the fourth month on. Males and females look alike. The Cat Ba langurs live in groups, usually one male with several females and their offspring. They are diurnal animals, adapted to living in limestone habitat. Each group has its own territory, defended by the adult male who also initiates the location of the group. The females usually give birth to a single baby every 2–3 years, which becomes mature at 4–6 years old. Langurs have an average life expectancy of 25 years. Food mainly consists of leaves, but also fresh shoots, flowers, bark, and some fruits.
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