Monkeys Were (Re)Introduced to Hong Kong to Get Rid of Poisonous Plants

If you ever go for a hike on Kam Shan, Lion Rock, or around the Shing Mun Reservoir, you may run into troops of wild monkeys. In fact, Kam Shan is so well-known for them that it is often nicknamed "Monkey Hill."

Hong Kong is home to two species of macaques: the rhesus macaque (Macaca mulatta) and the long-tailed macaque (Macaca fascicularis), as well as a hybrid species resulting from interbreeding between the two.

Although the rhesus macaque is native to Hong Kong—having been recorded in the New Territories and Kowloon as early as 1819—the macaques you see in the city today are not part of that original population. The waves of immigration that followed British colonisation in the nineteenth century led to human settlements encroaching on the native macaques' habitat, causing a rapid population decline.

However, when the British built the Kowloon Reservoir in 1910, they discovered Strychnos, a poisonous plant whose fruit contains toxic alkaloids. Out of fear that the fallen fruit would contaminate the water supply, the British introduced new groups of macaques in the hope that they would eat the fruits.

With food and water aplenty, these newly introduced macaques rapidly multiplied. As for the long-tailed macaques, they descend from a small troop allegedly released by a careless seafarer in the 1950s.