No segregation here; A long-tailed Macaque has joined a troupe of Dusky Langurs for the last 2 years.

My wife and I live in an apartment on Penang island overlooking the Strait of Malacca on one side and  surrounded by forest trees on the other sides.

 

Drone shot showing the forest surrounding our condominium.

The forested slopes of Pearl Hill host a number of species of native animals including  troupes of Dusky Langurs, foraging Long-tailed Macaques, Black Giant Squirrel sand  the much smaller Plantain squirrels. There are a number of troupes of 15-25 individuals on Pearl Hill and they appear to keep to a defined territory. For the last 3 years I have followed the local troupe when they come into view while foraging or making for their sleeping trees in the evening.

Long-tailed Macaque

Black Giant Squirrel

Plantain Squirrel

Long-tailed Macaques are opportunist eaters and will rob bins and eat what they can find. Long-tailed Macaques are also called Crab-eating Macaques and were confined mainly to coastal regions but with humans and their relaxed handling of food items and trash they have moved inland. They can still be seen to foraging on shorelines today.

Long-tailed Macaque with a Horseshoe crab

 Dusky Langurs are vegetarian and will eat leaves, flowers and fruit. Macaques can exist on fruit but will often take the easy option to eat anything that they can beg, borrow or steal.

Dusky Langurs seem to be rather laid-back compared with the sometime aggressive Macaques. Langurs have been seen in loose associations with other langurs including White-thighed Langurs (Surili) on Fraser's Hill. They have also been observed to form tighter associations with Silvered Langurs and will interbreed with them, which occurs in patchy forest remnants in Penang state..

Silvered Langur

Silvered Langur with a Dusky Langur (they can interbreed)

White-thighed Surili (they sometimes associate with Dusky Langurs)

Eighteen months to two years ago I noticed that a Long-tailed Macaque had joined the local langur troupe. It leaps with them, eats with them, plays with them and rests with them.

In Summary; 

They rest together

They eat together

The Macaque is bottom, right

They jump and move together (difficult to show in one frame)

What advantages does the Macaque derive by associating with the Langur Troupe?

One can only speculate as to why this association occurs. The forest around our condominium does not have many visitations from Macaques. They are generally not welcome as they can be destructive. The Langurs seem to know where the fruiting trees are and association with them would guarantee a constant supply of food. There are many trees that are prolific providers of fruit at different times of the year. 

There is always safety in numbers and the langurs have a good surveillance system that is sometimes assisted by their association with Racket-tailed Drongos.

The Langurs, as mentioned, seem to be a tolerant, non aggressive species and treat the macaque as their own.

Whatever the reason for the association they demonstrate to their human relatives that tolerance of differences is a virtue.