The crab-eating macaque (Macaca fascicularis), a species of monkey, is common in the reserve. The monkeys also enter the area surrounding the park and are common enough that there are concerns that interactions with people will alter their behaviour. Feeding the monkeys is prohibited, and visitors are urged to avoid staring at, baring teeth at or otherwise disturbing or threatening the monkeys. Monkeys are not the only mammals in the park. Other mammals include the Malayan pangolin (Manis javanica), Malayan colugo (Galeopterus variegatus), plantain squirrel (Callosciurus notatus) and slender squirrel (Sundasciurus tenuis). The colugos, which are generally nocturnal, can sometimes be seen clinging to trees during the day. Bukit Timah is the only place in Singapore where the red-cheeked flying squirrel (Hylopetes spadiceus) is found.