THEY break into kitchens, knock over flower pots while fleeing and hog overhead bridges, disrupting the lives of some Bukit Timah condominium residents.
In response to the rising number of complaints, the Agri-Food and Veterinary Authority told The Straits Times last week that it has been carrying out "monkey control operations" in the area.
In other words, moves have been made to trap and either rehome or kill the long-tailed macaques living there.
"It's getting worse and worse," said Ms Winnie Chang, an administrative officer who lives at Springdale condominium in Hindhede Road.
Monkeys have followed her along an overhead bridge outside her home and tried to grab her groceries, she said. "The only way is to get rid of them."
However, Ms Vinita Ramani Mohan, 34, who lives in a condominium even nearer the reserve, said she has had no problems with the monkeys.
"I find it puzzling and silly how people choose to move 'close to the green', and then are surprised when mosquitoes, monkeys, snakes and other inhabitants from the reserve areas wander into the condos."
In addition to catching monkeys, AVA lends traps to residents. Around 130 monkeys were caught in such traps last year, down from the 206 recorded in 2007.
The number of complaints about the "monkey nuisance" has risen lately.
AVA received 800 complaints in 2010, 730 in 2011 and 920 last year.
Assistant Professor Michael Gumert, who studies primate behaviour at Nanyang Technological University (NTU), pointed out that the rise in the number of complaints might not indicate an increase in monkey trouble.
Instead, it could be because AVA is doing more to reach out to residents. For instance, the agency started a 24-hour hotline in August last year.
It could also be because more people have moved into the area. The past few years have seen two new properties come up as well - Raintree condominium and Mont Timah cluster homes.
NTU research assistant Amanda Tan, who is working with Dr Gumert to study a troop of monkeys at Bukit Timah, said she spotted contractors two weeks ago with cages that contained oranges and bananas, just outside the Bukit Timah Nature Reserve near the Kampong Trail.
AVA said the monkeys are rehomed elsewhere whenever possible. The rest are euthanised, but AVA did not say what proportion of the monkeys caught were rehomed.
The National Parks Board (NParks) and AVA both urged the public not to feed monkeys. Doing so within nature reserves carries a fine of up to $50,000 or a jail term of up to six months, or both.
Residents should also keep food out of sight, tie garbage bags tightly, secure bin lids and close windows or install grilles.