Species Saturday

Species day; Sabangau’s delightful and deceptive Red Langurs

Distribution map of sub-species

This weekend (starting on a Friday – why not!) we release a special blog for Red Langur / Kelasi expert Dave Ehlers Smith (meet him here), getting to the bottom of why these little cheeky monkeys behave the way they do – meet the Red Langurs of Sabangau!..

“Red langurs (Presbytis rubicunda) belong the the subfamily of primates known as “colobine monkeys”, which are distinct in their specialised stomach adaptation which allows them to efficiently digest leaves and unripe seeds. A special sack in the stomach, similar to that found in cows and other ruminants, contains a delicate balance of chemicals and bacteria which break down the leaves that are generally indigestible to other “simple-stomached” primates. However, this balance means that colobines are unable to eat ripe fruits as other primates do, since the excess sugars present in ripe fruits causes an increase in stomach acids, which can prove fatal. This adaptation does however mean that in our forest, the monkeys get to the fruits before their cousins, the orang-utans, gibbons and macaques! They typically live in groups of about seven individuals, and the group comprises a single adult male, and up to three adult females with whom he mates. The adult male will then protect his females and their offspring from rival males which have not yet formed mixed-sex groups of their own. Colobine monkeys are found throughout Africa and Asia, but the red langur belongs to a fairly restricted genus of this subfamily, Presbytis, which is confined to Sumatra, Borneo and the lower Malayan Peninsular. The red langur itself is endemic to Borneo and the adjacent island of Karimata, and comprises five subspecies: P. rubicunda rubicunda, which is found in the east; P. r. ignita, in the central region of Borneo; P. r. chryseawhich is confined to Sabah in Malaysian Borneo, P. r. carimatae, only on the island of Karimata, and our own P. r. rubida, in the south-west portion of Borneo.

This white (now turned red!) baby is the newest
edition to one of the family groups.

The population density of red langurs in our mixed-swamp forest in Sabangau is relatively high within the genus of Presbytis monkeys, despite the fact that in the peat swamp forests there are very few nutrients available in the soil. However, we have found that the low-pole environment, deeper into the forest interior, is not capable of supporting populations, almost certainly due to the lack of large trees producing their favourite foods, unripe seeds. In fact, our research suggests that there is such a constant supply of fruits in the mixed swamp that they are less reliant on leaves than colobine monkeys in other forests. Furthermore, this constant supply of fruit means that they also range further to obtain this high quality food than other leaf-eating monkeys.

Classic mother child differences –
when to stop playing!

Red langurs are generally considered less threatened than other primates on Borneo due to their broad distribution across the island; however, the extreme rates of deforestation and habitat conversions for agriculture such as oil palm means that even a monkey with such a large range as this is starting to feel the pressure of humans on their environment. In the last 10 years, red langurs as a whole have lost 10% of their habitat (and as much as 20% for some subspecies), and furthermore, research by Dr. Andrew Marshall in Gunung Palung suggests that numbers are so low up in the hills higher than 700 metres above sea level that they may not be able to support viable populations. This is a worrying sign for the conservation of red langurs, since much of Borneo’s remaining forests, and particularly its protected areas, are at higher elevation. Therefore, it’s vital we make efforts to understand the ecology of this fascinating and unique monkey while we still have the chance, to save both it and its habitat.”

A very good view – usually
these fellas stay very hard to spot!

Thanks for such a perfect overview Dave – hopefully the red little guys will see you back in Sabangau very soon!

Make sure you keep up to date with our intern vacancies and all our research via our facebook and updated website. See Dave’s papers on our publications page!

Dave Ehlers Smith , Thea Powell