Community of Proboscis monkeys sitting in a tree.

This fast-growing tourism sector where tourists can conveniently reach primates via motor boats is causing stress-related behaviours in monkeys

24 April 2022

3 min read

New research shows that the increase in primate ecotourism is having a negative effect on monkey’s behaviour.

The study, led by the University of Portsmouth, found that this fast-growing tourism sector where tourists can conveniently reach primates via motor boats is causing stress-related behaviours in monkeys.

The research looked at the impact of a single engine motor boat approaching a community of proboscis monkeys, an endangered species living in a remote riparian area (strips of vegetation that border rivers, streams and lakes) in Sabah, Malaysia. Proboscis monkeys are unusual looking with their very long noses, which adds to making them appealing to tourists.

Many of these boats, carrying multiple tourists, approach the primates quickly and loudly, often reaching the river banks just a few metres away from the wildlife.
The researchers found that frequent visits by such groups, which often involve an unusually high level of noise, caused stress-related behaviours in the primates such as self-scratching, an increased vigilant state, increased levels of aggression and reduced feeding.

Proboscis monkey. Copyright Rudi Delvaux

Lead author of the study, Dr Marina Davila‐Ross, Reader in Comparative Psychology at the University of Portsmouth, said: “Our evidence shows that even a single motor boat moving slowly, with humans behaving calmly, can negatively affect the primate’s behaviour and induce stress — an impact that is likely to be larger with tourist boats.

“The riparian area is an important habitat that has become increasingly popular to primate ecotourism, because it enables tourists to conveniently reach primates via motor boats.”

The researchers conducted the experiment by approaching the monkeys in a motor boat with different speeds and travel distances - fast-close (approaching the monkeys for 10 seconds when 40 metres away at a speed of 14.4 km/hr), slow-close (approaching the monkey for 40 seconds when 40 metres away at a speed of 3.6 km/hr), and slow-far conditions (approaching the monkeys for 20 seconds when 100 metres away, at a speed of 3.6 km/hr). For each condition, they compared stress-related behaviours before the boat approached with after the boat started its approach.

Our evidence shows that even a single motor boat moving slowly, with humans behaving calmly, can negatively affect the primate’s behaviour and induce stress — an impact that is likely to be larger with tourist boats.

Dr Marina Davila‐Ross, Reader in Comparative Psychology

The results showed that the monkeys displayed stress-related behaviours for longer in the fast-close and slow-close conditions and also reduced feeding as a result of the boat approaching in the fast-close condition. They also found that male proboscis monkeys displayed more vigilant behaviour than females.

Once the boat started to approach, the proboscis monkeys gazed at the boat for longer than before the boat approached, showed repeated scratching, and often moved quickly backwards to hide in the trees. This could potentially cause the monkeys to leave their safe sleeping sites and to retreat deep into the forest as it gets dark, where they could face a higher risk of predation.

Dr Davila‐Ross said: “Collectively, our findings suggest that the approach of a single motor boat induces stress in proboscis monkeys when approaching them as closely as 60 metres from the other side of the river, regardless of the speed of approach. The findings match those obtained in studies on sea mammals and birds, suggesting that stress is a universal response across animals when a boat approaches — a large, loud, and artificial object moving toward them is likely to be threatening.”

Our study highlights the importance of keeping a distance from proboscis monkeys and perhaps also other primates in the riparian area when in motorboats.

Dr Marina Davila-Ross, Reader in Comparative Psychology

The researchers propose that guidelines for primate tourism in the riparian areas, which are largely unregulated, should include an approach speed of no more than 4 km/hr within 100 metres of the proboscis monkeys. They suggest it is also important to keep a distance, preferably no closer than 60 metres away, from the monkeys.

Dr Davila‐Ross added: “Our study highlights the importance of keeping a distance from proboscis monkeys and perhaps also other primates in the riparian area when in motorboats, and preferably approaching them similarly as in the slow-far condition, where we observed no impact. Such information might be helpful for tourists, allowing them to modify their behaviours when visiting the primates and when encouraging guides to follow the guidelines.”

The study is published in the International Journal of Primatology.