Proboscis monkeys are stressed out by tourist boats

Proboscis monkeys are fascinating to tourists, and perhaps even more so than other monkeys due to their oversized noses. Areas along rivers are popular for tourists visiting Sabah Malaysia because they can approach monkeys and other wildlife via motor boat. 

Tour boats move quickly and loudly through the forest and toward the monkeys, approaching at close proximities. Now, new research led by the University of Portsmouth shows that proboscis monkeys are often stressed by the arrival of these tour boats. 

“Our evidence shows that even a single motor boat moving slowly, with humans behaving calmly, can negatively affect the primate’s behavior and induce stress – an impact that is likely to be larger with tourist boats,” said study lead author Dr. Marina Davila‐Ross. “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 scientists carried out the research by driving motorboats toward the monkeys at various speeds and distances. Under the conditions of fast and close, slow and close, or far and fast, the monkeys exhibited stress behaviors.

“Collectively, our findings suggest that the approach of a single motor boat induces stress in proboscis monkeys when approaching them as closely as 60 meters from the other side of the river, regardless of the speed of approach,” said 

Dr. Davila‐Ross.

“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.”

The stress can potentially cause the monkeys to move into more dangerous territory. For example, a monkey leaving a safe spot close to nightfall might be more vulnerable to predators and other threats. 

“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,” said Dr. Davila‐Ross. “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 researchers suggest that guidelines for tourist boats visiting proboscis monkeys should be enacted. Ideally, boats would move no more than 4 km/hr within 100 meters of monkeys and, most importantly, come no closer than 60 meters.  

The study is published in the International Journal of Primatology.

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By Zach Fitzner, Earth.com Staff Writer