Thomas's Leaf Monkey

Thomas's leaf monkey, also known as the North Sumatran leaf monkey, Sumatran grizzled langur, and Thomas's langur, is endemic to northern Sumatra (Aceh and North Sumatra provinces). 

 

Range of Thomas's leaf monkey from Wikipedia.

Leaf monkeys, langurs and lutungs are Old World monkeys found in Southeast Asia. Thomas's leaf monkey is easiest to find in Gunung Leuser National Park where it is protected. 

 

Near Tangkahan.

All of the ones we saw were in Gunung Leuser NP, on the east side near Tangkahan and Bukit Lawang. It has a funky head, including a black mohawk with white stripes on either side, a white stripe around the sides of its face, like goggles, and facial hair that juts out to the side like a long mustache. It has black hands and feet and is otherwise mostly gray with a white belly, neck and the underside of its arms and legs.

Near Bukit Lawang

The IUCN rates it as Vulnerable. A study concluded in 2005 estimated that the number had declined by 30% over the last 40 years, much due to habitat loss from logging and palm oil plantations, but also due to the illegal primate trade, body parts being sold for use in medicinal remedies and by local farmers who cull them as "crop pests." 

Near Bukit Lawang

They inhabit tropical dry forests and rubber tree plantations provide an alternative habitat. The first ones we saw near Bukit Lawang were on the edge of a rubber tree plantation.  

Near Tangkahan.

They eat mostly leaves, as indicated by their name, and love snails. Males watch for predators while females go to the forest floor to look for snails.