“Our treatment of animals will someday be considered barbarous. There cannot be perfect civilization until man realizes that the rights of every living creature are as sacred as his own”
David Starr Jordan
These poor little monkeys are now mistakenly swinging on power cables instead of vines. Needless to say, they don’t last very long! They are also getting hit by cars on roads – again, it goes without saying, they are not very familiar with traffic! But, they have lost their own habitat due to man and are now forced to live in close proximity to the same.
Next, conflict arises as man declares the monkeys a nuisance for stealing his crops – a common local pest, in fact. Failing to take into account that he has stolen the home and food supply of the animals, he then sets about persecuting them. And, just to exacerbate matters in this ‘man versus monkey’ war, through this forced move, the purple-faced langurs have become more tolerant of human beings, and, as a result, have made themselves easy targets.
There are four species of purple-faced langur in Sri Lanka, and all are endangered, one of them critically. They have been fiercely driven out of their natural forest habitat and forced to find food within the gardens and rubber plantations of the invaders, which they now depend upon for their survival. The food they are now eating through necessity is far from adequate for these monkeys. They, like several other species, have specialized stomachs which use symbiotic bacteria to aid digestion. In their natural habitat, much of their nutrients and energy are derived from the complex carbohydrates contained in leaves. Now, they must rely on cultivated fruits which are loaded with simple sugars and are difficult to absorb.
No two sub-species of purple-faced langurs are the same – their coats and cranial features vary. But, overall we can see a dark-brown to black colour on the body, legs and arms. The species sports pale to dark whiskers which sweep backwards. Contrary to their name, they do not have purple faces – more of a grey-black colour. They all have long arms and reduced thumbs. Males can reach a body length of twenty-five inches, with a much longer tail length of thirty-three inches. They can weigh up to twenty-one pounds. Females, as you would expect, tend to be slightly smaller.
Purple-faced langurs live for a quite a long time, and life spans of twenty-six years have been recorded as normal.
Also known as purple-faced leaf monkeys, these primates have a one-male social system, very occasionally two, with a ratio of one male to one to seven females and assorted juveniles and infants. The male will defend this group, or troop, aggressively against other males coming attempting to encroach.
There are also all-male groups consisting of anything between two and fourteen individuals. These groups will forage separately in daylight and regroup at night to sleep.
The purple-faced langurs use three loud forms of communication; whoops, barks and residuals. These sounds are used to alert others to predators, in defence of the group and its territory, attract suitable mates, and locate other members of the troop. Adult males tend to be the loudest and most vociferous. These vocalisations help conservationists, who have difficulty seeing the monkeys in the trees, to identify the species.
There is little information about the breeding season of the purple-faced langurs available. I suspect this may be because it is an all year round occurrence. There is a gestation period of up to two hundred and ten days, after which one infant will be born, weighing just under one pound. The infant’s coats are a contrast to their parents in that they are pale grey with a brownish tinge on the top of the head, arms, legs and chest. The little ones start to eat solid food at about twelve weeks and will be fully weaned by eight months.
In general; monsoon scrub, dry evergreen forests, mature secondary forest, undisturbed cloud forest, montane tropical forest and semi-deciduous forest. Each sub-species has its own preference.
The southern lowland purple-faced langur (Trachypithecus vetulus vetulus) lives in the rainforests of southern Sri Lanka.
The western purple-faced langur (Trachypithecus vetulus nestor) inhabits the wet zone of western Sri Lanka.
The northern purple-faced langur (Trachypithecus vetulus philbricki) can be found in the north and east of Sri Lanka, in the dry zones.
And, the bear monkey, or montane purple-faced langur, (Trachypithecus vetulus monticola), occupies the mountains of central Sri Lanka.
What they eat
They are mainly folivorous, but, as needs must, will eat fruit, flowers and seeds (from gardens).
Loss of habitat is the greatest threat to these little primates. Because of this, they are simply not getting enough of the right food any more. There are various reasons for habitat loss, depending on the area the primates are located in, but, collectively the reasons are rapid urbanization, selective logging, encroachment for agriculture, and development for infrastructure and industry. Occasionally, in the north-east, they have fallen victim to cyclones. Hunting is also a threat, either for the pet trade, subsistence or the bushmeat market (this is not a significant amount). Skins are used, by some, to make tribal drums. They are electrocuted by power lines and hit by cars on the roads. Human conflict over crops and encounters with dogs are also becoming far too common.
Three sub-species of purple-faced langurs (Trachypithecus vetulus) are listed on the IUCN Red List of Threatened Species as Endangered. The sub-species western purple-faced langur (Trachypithecus vetulus nestor) is listed as Critically Endangered, and, is also classified as one of The World’s 25 Most Endangered Primates 2012-2014. All purple-faced langur species are listed on CITES Appendix II.
Exact population numbers are unknown, but it is widely acknowledged these once highly prevalent monkeys are declining at an alarming rate. Various agencies are working to minimise the threats to the purple-faced langurs, such as building corridors and rope bridges within protected areas.
A few southern lowland purple-faced langur (critically endangered) are known to be kept in captivity.