The rainforest of Gunung Leuser National Park and the area where you will trek is home to the last remaining population of Sumatran orangutan. It is also home to other critically endangered and unique species that you can not see anywhere else in the world. To help safeguard the future of the forest and its wildlife it is really important for visitors to understand the impact their presence can have and what they can do to minimise that impact.

The problem:

Wild orangutans spend most of their time high in the forest canopy. They do not come to the ground very often and rarely come into contact with humans. BUT...the ex-captive orangutans which inhabit the forest in BUkit Lawang frequently walk on the ground and often come into close contact with humans. This behaviour is not normal.

Their behaviour and the behaviour of human visitors is making them sick.

Why can orangutans get sick after contact with humans?

Orangutans are genetically very close to humans (97%) and can catch many of our diseases. Measles, TB, pneumonia and influenza are spread when you cough, sneeze or spit. Shigella, Hepatitis A, Herpes, scabies, polio and worms are carried in human faeces.
• The measles virus can be carried great distances in open air.
• The polio virus can survive for many months in soil.

What may be a simple cold or cough for us could be very dangerous for orangutans and there is a chance that humans could be affected by diseases that orangutans may carry.

What can be the effect of too much human contact?

Orangutans may look like they are OK around humans but their natural behaviours are disturbed. Any prolonged change to natural behaviours can cause very high levels of stress to their bodies. Stress can lead to problems such as heart failure, poor reproductive health, high infant mortality, depressed immune system (making it easier to get sick) and ultimately may result in premature death!

What can you do to help stop this happening?

This is easy...simply follow the rules. Tell your guide you have read the rules and wish to follow them. You can also tell your friends and fellow trekkers. If you see anyone breaking the rules please inform your guide

              The rules apply to ALL wildlife.

 By doing this you will…..

  • Have a safe and natural experience
  • Minimise disturbance to the forest and ALL wildlife
  • Help stop orangutans getting sick.
  • Preserve forest for future generations

Possible effects of too much human contact:

Feeding monkeys and gibbons changes their normal behaviours and can cause competition for food and aggression within group and possibly to humans.

Feeding the great argus pheasant can change its feeding and territorial patterns and this effect its breeding.


Borneo: High orangutan infant mortality rate in rehabilitation centre.

Thailand: Gibbon dead from human herpes infection.

Africa: Chimpanzees die from human  flu, ebola, polio: 

 (information taken from published articles in scientific journals)



RULE 1: The recommended maximum number of visitors per group is 7:this controls the risk of human impacts and optimises your viewing experience

 RULE 2: At the feeding platform you are allowed to stay for a maximum of ½  hour. If you meet orangutans when trekking you must stay with them for no longer than 10 minutes.

 RULE 3: Visitors who are sick are not allowed to go trekking or to the feeding platform.

Please report any sickness to your guide and your visit can be rescheduled. Your guide can refuse a visit to anyone showing obvious signs of illness. If you have a cough/cold you should wear a face mask.

 RULE 4: Healthy visitors should not be closer than 10 meters from orangutans. Visitors who have a cough/cold should not be closer than 20 meters.

 RULE 5: When you are close to orangutans you should behave properly:

  • Do not call the orangutans.  
  • Do not feed the orangutans or give them drinks.
  • Do not smoke, eat, drink, cough, sneeze or spit.
  • Always stay in a close group and never loose contact with your guide.
  • You should sit when watching the orangutans.
  • Be as silent as possible and use good body language (no shouting, no sudden movements, no making monkey sounds etc)
  • Do not clear vegetation to get a better view.
  • Do not stare at the orangutans or use binoculars/cameras/videos if they are disturbed(kiss-squeak vocalisations and dropping branches are signs of stress and anger)
  • Do not use flash photography. It will not be effective anyway.
  • Do not approach orangutans and NEVER come between a mother and her baby.

 If an orangutan comes close and you can not move away calmly do not touch them. If they take your bag DO NOT try to fight them for it. Your guide may be able to get it back later. You should only bring essentials to the forest. Your health and your safety is more important than your bag!


RULE 6: When you are in the rainforest behave properly at all times:

  • ALWAYS follow the instructions of your guide.
  • It is forbidden to enter the rainforest without a guide.
  • Do not pressure your guide to get closer to animals or give them food so you can take photographs.
  • If you feel your guide has behaved inappropriately inform the guide office, your guest house or the national park office.
  • Do not leave any litter in the forest e.g. tissues, water bottles, cigarette ends, food scraps.  It must be carried outside of the forest then disposed of. This includes fruit skins which may carry your germs.
  • If you must defecate you should dig a hole at least 2 feet deep. You can borrow a parang/machete from your guide. All faecal material and tissue must be buried.
  • Do not disturb or collect anything from the forest such as flowers, insects, seeds etc