The lion-tailed macaque (Macaca silenus) is a reclusive monkey species native only to India. They are locally called "vandaru", which got corrupted into English as "wanderoo".
A member of the family Cercopithcidae, this macaque prefers to live in mature rainforests (particularly the Anamalai in southern India and the western Ghats). It is the only type of macaque that is both truly arboreal and limited to living in rainforests. The species is terribly endangered; perhaps only a few hundred to a few thousand of them remain alive in the wild.
They are in trouble partly due to their low reproduction rates (females can only give birth to one baby a year) and partly due to habitat loss from logging and agriculture. Some of them have also been hunted for food and for folk remedies. Many have been killed by domestic dogs.
Unlike some other monkey species, they have been unable to adapt to living near human towns and cities. They will hide from people, and they are much more likely to be heard than seen. Their loud cries sound eerily human.
As their name implies, these monkeys have long, tufted tails. Their bodies are covered in long, shiny black fur, and they have a mane of light gray fur. They are truly beautiful and unique animals, which perhaps makes their decline all the more tragic.
They live in troops of 12-30 monkeys (up to three will be adult males, and the rest will be females and youngsters) and are active during the day. The females are somewhat smaller than the males, weighing an average of 5 kilograms versus 7 for the males. Females will stay in the group they're born to their whole lives, but young males will leave to seek another group right as they hit puberty.
Like other monkey species, they will behave aggressively toward unfamiliar troops. Males will herd their females defensively and solitary females will try to run off unknown males, because invading hostile males will often commit infanticide to force females into fertility so that the invaders can rape and impregnate them. Once the troops have gone through the requisite screeching and teeth-showing, if neither proves to be a true threat, things will calm down and the two groups will coexist on friendly terms.
These monkeys eat a diet of fruit and leaves supplemented with a few insects now and then. Jackfruit and cullenia are some of their favorites. They have cheek pouches to store food while they forage on the forest floor.
Zoos are working on conserving this species, especially the San Diego Zoo. The lion-tailed macaque was the first species their Center for Reproduction of Endangered Species studied. Their work has greatly increased the success of breeding these monkeys in captivity. So far, there are about 500 of these macaques alive in 21 zoos worldwide
References:
Experimental Intergroup Encounters In Lion-Tailed Macaques. Zinner, D., Hindahl, J. and Kaumans, W. Available at http://www.dpz.gwdg.de/pr/pr59/zinner.pdf
http://www.sandiegozoo.org/conservation/fieldproject_macaques.html
http://www.primate.wisc.edu/pin/factsheets/macaca_silenus.html
http://www.pbs.org/edens/anamalai/creatures.html