Macaca silenus is a member of the silenus group. The other phylogenetic sister species in this group include M. leonina, M. siberu, M. nemestrina, M. pagensis and the seven Sulawesi species.

Lion-tailed Macaque is listed as Endangered as the total number of mature individuals is less than 2,500, with no subpopulation having more than 250 mature individuals. There are estimates of a continued decline of over 20% of the populations in the next approximately 25 years, along with hunting, road kills and continued loss of habitat.

This species is endemic to the Western Ghats hill ranges in southwestern India from the Kalakkad Hills (8°25’N) north to Sirsi-Honnavara (14°55’N) (Fooden 1975, Santhosh et al. 2013), at altitudes of 100-1,300 m in the states of Karnataka, Kerala, and Tamil Nadu. Although the species has a relatively wide range, its area of occupancy is small and severely fragmented (Molur et al. 2003, Singh, 2019).

The total wild population is estimated to be about 4,000 individuals, made up of 47 isolated subpopulations in seven different locations; these subpopulations tend to be small and in forest fragments that are isolated from each other (Molur et al. 2003, Singh et al. 2006). There are estimated to be fewer than 2,500 mature individuals (Molur et al. 2003). Few subpopulations have the structure and habitat suitable for self-sustainment, where 10-15 groups share or connect their home ranges and interbreed. In the Sirsi-Honnavara rainforests of the northern Western Ghats in Karnataka, for instance, a subpopulation consisting of 32 groups in a contiguous tract of habitat exists where less than six groups survived 20 years prior in the early 1980s (Kumara and Singh 2004). Kumara and Singh (2008) estimated 451 individuals in 30 groups in Kudremukh forest complex. Recent sightings reported by Kumara and Sinha report of population in the following areas: one group in Makut Reserve Forest, four groups in Talakaveri Wildlife Sanctuary, one group in Subramanya Reserve Forest, one group in Sakaleshpur Reserve Forest, 10 groups in Kudremukh National Park. Kumara et al. (2011) reported a decline in habitat in Aghanashini Lion-tailed Macaque Conservation Reserve. The forests of Kerala host up to 1,216 adult lion tailed macaques, according to a large study using estimates from forest sightings (Easa et al. 1997).  The Anaimalai landscape support about 60 groups, though only two subpopulations there are composed of more than two groups, one has seven, the other 12 (Singh et al. 2002, Kumara et al. 2014). Overall the species is declining in forest fragments, and stable in protected areas (Molur et al. 2003, H.N. Kumara pers. comm). The northern-most population in Anshi Ghat has been extirpated (M.S. Ram in little. December 2019), making the present northern-most location Sirsi-Honnavara.

In a recent study by Ram et al. (2015) on genetic diversity studies on Lion-tailed Macaque across its range in the Western Ghats, they found two distinct populations of ancient lineage north and south of the Palghat gap dating back to 2.11 million years ago.  Ram et al. (2015) recommend distinct conservation measures for the two populations although currently they are not assigned taxonomically.

Mainly arboreal, this species prefers the upper canopy of primary tropical evergreen rainforest (Singh et al. 2002) referred to as Sholas but may also be found in monsoon forest in hilly country with canopies reach 30 to 50 m and in disturbed forest. It is even known to persist in areas with human planted fruit trees such as Jack fruit, guava, passion fruit, and others, although populations fluctuate based on fruit tree availability within a forest fragment. They range in elevation from 100 to 1,800 m (Molur et al. 2003).

The species seems largely to be a seasonal breeder, with births temporally clumped along with the fruiting season dictated by monsoonal climate (Singh et al., 2006). In the wild females first give birth at about 80 months, and have an interbirth period of about 34.3 months. The generation length is approximately 13 years.

The major threat to this species today is habitat fragmentation, with many of these fragments being further decreased. In the past, habitat loss was due mainly to timber harvest and the creation of exotic plantations such as tea, eucalyptus and coffee. Habitat degradation seems to the biggest threat to the conservation of Lion-tailed Macaques wherever they occur in Kerala (Easa et al. 1997). In private forests and plantations, change in land use is a problem for the species. Hunting is a second major threat, especially in certain parts of its range. In one location, Coorg, with a large area of remaining wet evergreen habitat, the species is highly threatened by non-subsistence and subsistence hunting for food (Kumara and Singh 2004). In some areas, primate meat is preferred as food, and so the animals face serious hunting threats (Kumara and Singh 2004). A local trade exists for pets (Molur et al. 2003), and in Coorg the animals were often hunted in the past for “medicinal” uses. 

Certain features of the reproductive biology and ecology of this species (such as large interbirth periods, seasonal resource availability, and female competition for mating opportunities) combine to make it intrinsically rare in the wild. The populations already reduced to low numbers are in special need of active management (Singh et al. 2006). Furthermore, the Lion-tailed Macaques in the fragmented forests of Anamalai Hills were found to have less genetic diversity compared to those in a more contiguous forest in Nelliyampathy, implying that genetic inbreeding due to fragmentation and isolation may have a detrimental effect on the long-term survival of small, isolated populations (Ram et al. 2015).

The following conservation measures are recommended for this species:

• There should be better management of private lands, which hold perhaps a quarter of the remaining populations: this would ideally include maintaining coffee and cardamom plantations, prevent conversion into tea, habitat quality improvement.

• Prevention of road kills, prevention of provisioning by tourists and others.

• Prevention of hunting which is endemic to some areas.

• Retention and restoration of critical connectivity between forest patches.

• Maintaining a sustainable captive population.