Underground Burrows to High Canopies: Mammals of the Southern Western Ghats

High up in the canopy of a patch of rainforest, a camera trap is strapped to a tree trunk. Left to gaze fixedly at the branch ahead, its infrared sensors idly scan the foliage until a cloud of warmth approaches; the trigger goes off and the camera snaps a picture — a brown palm civet (Paradoxurus jerdoni) on its nightly search for berries.

This and other camera traps have been deployed to document the mammals found in a part of the southern Western Ghats. This ecological region stretches south of the Palghat (Palakkad) gap, through parts of Tamil Nadu and Kerala, to the southern tip of the country. The lower elevations in this region are primarily composed of moist deciduous forests and rainforests, home to a range of mammals. Elephants and gaur routinely traverse these habitats, as do large predators like leopards and tigers. Squirrels, macaques, and langurs bound in the canopy overhead while more elusive mammals like civets and mouse deer wait for the cover of night to venture out. As you climb these hills, the landscape transforms into a matrix of shola forests and grasslands. Nilgiri martens (Martes gwatkinsii) hunt in the sholas, while the grasslands at the top are worked on by herds of Nilgiri tahr (Nilgiritragus hylocrius).

Over 120 species of mammals have been recorded across the full expanse of the Western Ghats. Of these, 15, including the brown palm civet, Nilgiri tahr, and lion-tailed macaque (Macaca silenus), are endemic to this region. Like the rest of the Western Ghats, however, much of these habitats in the south have been replaced by commercial plantations — a shift that began with vigour during the colonial era and continues to date.

Such changing land use has thrown wildlife here into the limelight — animals that once melted into the forests with relative ease stand out in sharp contrast against open landscapes like tea estates. Some mammals have adapted to thrive in these spaces. Leopards, for example, have learnt that dogs found near human-dominated areas make for easy pickings. On the other hand, some animals cling to fragments of undisturbed forest and grassland for survival. 

While the Western Ghats set the stage for a wide range of mammalian characters, a few charismatic species typically steal the show. The Nilgiri tahr is a strapping goat confined to sprawling sky islands — shola-associated grasslands spread across mountaintops — at elevations above 1,200 m. A tahr-specific conservation project undertaken by the Tamil Nadu Forest Department has shed more light on its current distribution and areas it could have occupied in the past. References to “varudai” or “varaiyaadu”, as it is known in Tamil, have been found in Sangam literature and other old Tamil works. 

In the evergreen forests below, the canopy is occupied by troops of lion-tailed macaques, named for the lion-like black tuft at the ends of their short tails. These troops are hierarchical and highly territorial, defending their home ranges with shrieks and bared teeth. Such encounters can even escalate to physical altercations between troops. 

Besides these endemics, more widespread mammals like (1) Asian elephants (Elephas maximus) and (2) Indian leopards (Panthera pardus) also roam the southern Western Ghats. The size, social behaviour, and advanced cognitive abilities of elephants contrasts with the solitary, elusive nature of leopards, as these two species find their own ways to thrive in the same landscape.

Among the more overlooked mammals found here are members of the family Sciuridae, the squirrels. In the Western Ghats, these bushy-tailed mammals range in size from nearly 1.8 kg in the case of (1) the Malabar giant squirrel (Ratufa indica), to less than 50 gm in the case of smaller species such as the Nilgiri striped squirrel (Funambulus sublineatus) and the (2) jungle palm squirrel (Funambulus tristriatus). Squirrels are important seed dispersers in this landscape as well as prey for certain predators. Giant squirrels are hunted by leopards, while smaller ones are picked up by raptors and even the occasional great hornbill (Buceros bicornis). As these squirrels move through the trees, they typically use connecting branches to navigate the canopy; some squirrels, however, are unconstrained by such corridors. 

Spreading their limbs to unfold furry membranes stretched between their wrists and ankles, Travancore flying squirrels (Petinomys fuscocapillus) simply glide between trees. These small, nocturnal squirrels are quite hard to spot and were thought extinct in India for about a century until rediscovered in Kerala in 1989. 

Besides the flying squirrel, several mammals such as (1) porcupines and (2) Indian brown mongooses are active at night in this neck of the woods. The Indian crested porcupine (Hystrix indica) is a widespread rodent found in a broad range of habitats across central and southwest Asia. Spending the day in burrows in the ground, it emerges at dusk to forage through the night, constantly on the lookout for danger. When it senses a threat, it raises its quills to appear larger and can even charge backwards into the threat if necessary. 

The brown palm civet is endemic to rainforests of the Western Ghats and predominantly frugivorous in its feeding habits; it acts as a key seed disperser in these habitats. With these rainforest patches becoming increasingly fragmented, the occurrence of these civets is driven by the diversity of fruit trees available to them in these changing landscapes. 

As rainforest patches in the Western Ghats are interspersed with commercial plantations and accompanying human habitation, the adaptability of mammals found here is tested intensively.

While many animals, such as the lion-tailed macaque and Asian elephant, appear well-suited to changing habitats, these adaptations don’t necessarily bode well for the long haul. Lion-tailed macaques have been observed to modify their behaviour in human-dominated spaces. Macaques in more urbanised areas have learnt to approach humans as potential sources of food. Such interactions increase the possibility of human-animal conflict, as well as the spread of parasites from humans to macaques. Macaques also face challenges in terms of poor canopy connectivity in fragmented areas, leading to more instances of roadkill. Measures such as the installation of canopy bridges across roads and the maintenance of native fruit trees in shade-grown coffee plantations could help mitigate the negative effects of habitat fragmentation on the mammals found in this rich landscape.