These results suggest that dusky leaf monkeys are sexually dimorphic species, as the females were found to be, on average, 12% smaller than the males sampled.

Research conducted within the country between 2019 and 2020 revealed that three dusky leaf monkey individuals were located in August 2019 within the northern region of the island, near the body of water that borders Singapore and Malaysia.

Researchers are concerned about these migratory patterns because these primates can increase competition for resources, such as vegetation, and transfer diseases and pathogens to other native species that are not equipped to recover from them.

Numerous activity budgets have been conducted across Malaysia to study the behavioural patterns of the dusky leaf monkey.

[14] Ten years prior, another activity budget with 18 dusky leaf monkeys was conducted at the Penang Botanical Garden, which is also located in Malaysia.

[citation needed] However, a more recent study conducted in Malaysia from November 2017 to February 2018 in Bukit Soga Perdana, a forested area that is heavily influenced by industrial activity, concluded that the dusky leaf monkeys sampled spent the majority of their days moving, although these results were skewed due to unfavourable weather conditions that occurred during observations.

A study conducted in 1996 by researchers at the University of St. Andrews revealed that, after a group of dusky leaf monkeys engage in aggressive behaviour, conflict resolution occurs more frequently and much faster afterwards than within other primate species.

In fact, reconciliation among dusky leaf monkeys can occur as quickly as 60 seconds after fighting, and can be instigated by either the aggressor or the receiver through gestures such as embracing.

Burton concluded that the seminiferous tubules within each gonadal remained the same size throughout the year, and that there was no evidence of seasonal variation in testicular weight.

[20][18] While the dusky leaf monkey is often killed for their meat,[2] there are other incentives to poach them as well, as they are considered agricultural pests across Southeast Asia.