A specialist of the sky islands
The Nilgiri tahr (Nilgiritragus hylocrius) is an ungulate found only in the high-altitude grasslands of the Western Ghats in southern India. This mountain goat lives on the steep, rocky cliffs at elevations between 1,200 and 2,600 meters. Its habitat consists of montane grasslands interspersed with pockets of stunted evergreen forests called "sholas". The tahr is a master of this terrain, possessing specialized hooves with a hard outer rim and a soft, convex inner surface that provides exceptional grip on near-vertical rock faces.
Adult males, known as "saddlebacks," are larger than females and develop a distinctive light grey patch on their backs. Both sexes have curved horns; a male's can reach up to 40 cm, while a female's is typically slimmer and shorter. These animals are primarily crepuscular, meaning they are most active during dawn and dusk, feeding on grasses and small shrubs. During the day, they often rest on high, inaccessible cliffs, which are a refuge from predators like leopards and dholes (Asiatic wild dogs). The total wild population was estimated to be 2,655 individuals in a 2025 joint survey by the forest departments of Tamil Nadu and Kerala.
A fragmented existence
The Nilgiri tahr is classified as an endangered species by the IUCN. Its population suffered a dramatic decline in the late 20th century due to unregulated hunting and habitat loss, with numbers dropping to only a few hundred individuals. This created a severe genetic bottleneck, drastically reducing the genetic diversity of the entire species. The remaining tahr now exist in small, fragmented populations scattered across a 400 km stretch of the Western Ghats.
This isolation is amplified by natural geographical barriers. The Palghat Gap, a 41-km wide low-lying pass through the Western Ghats, is a significant barrier to gene flow. Genetic studies of the mitochondrial Cytochrome b gene reveal a clear divergence between the tahr populations north of the gap and those to the south. The FST value, a measure of population differentiation, between these groups is 1, which shows a complete absence of genetic exchange. This prolonged isolation, driven by both historical climate changes and modern habitat fragmentation, has put the northern and southern populations on separate evolutionary paths. Over time, this genetic drift may lead to the formation of distinct subspecies, a process known as allopatric speciation.