A black-tufted marmoset, which is a rare species of monkey, has been rescued in Punggol, the fifth to be found so far this year in Singapore.
It is likely that the animal, which is native to Brazil only, had been smuggled into Singapore to meet the demands of the illegal exotic pet trade, said primate scientist Andie Ang, who chairs the Raffles' Banded Langur Working Group.
Given the relatively small size of the monkey - about 20cm in height and 350g in weight - it could have been brought into Singapore by land, sea or air, Dr Ang added.
The monkey is being cared for at the Singapore Zoo, after it was rescued by the Animal Concerns Research and Education Society (Acres) on Sunday.
It was first spotted near Block 271D in Punggol Walk by a member of the public last Saturday. But when an Acres rescue team arrived at the site, it was nowhere to be found.
The next day, another member of the public found the marmoset and managed to contain it in a cardboard box. It spent the night at the Acres Wildlife Rescue Centre before being transported to the zoo on Monday.
For every marmoset that is delivered to a customer, nine others would have died along the way.
In April, four marmosets were found abandoned outside a clinic in Serangoon Road. Two of them were in a wooden box, one in a carrier and another in a plastic Tupperware box. All four animals were rescued by Acres and sent to the zoo.
Ms Anbarasi Boopal, deputy chief executive of Acres, said that while many people might think it is cool to keep exotic pets and that they can provide for them, such wild animals have diverse needs that are often impossible to meet in captivity.
She urged exotic pet hobbyists to consider the welfare of the animals and the cruelty of keeping them in captivity.
She also noted that listings of live animals on online trading platforms are growing at an alarming rate and emphasised the urgent need for specific regulations that govern the online sale of these animals.
Dr Ang said that for every marmoset that is delivered to a customer, nine others would have died along the way due to factors such as poor diet and diseases.
"These primates are highly intelligent and mobile; keeping them at home would be detrimental to their physical and mental health," she said.
Under the Endangered Species (Import and Export) Act, it is an offence to import, possess, display or sell such animals.
A person convicted under the Act is liable to a fine of up to $50,000 for each species or a jail term of up to two years, or both.