Nilgiritragus hylocrius [Ogilby, 1838].

Citation:Proc. Zool. Soc. Lond., 1837:81 [1838].

Type locality:India, Nilgiri Hills.

The taxonomic record (above) is taken from Wilson and Reeder (1993). Originally, this tahr was assigned to the (now invalid) genus Kemas, and was included within Capra by some 19th Century authors (see Lydekker, 1913). Until 2005, the Nilgiri tahr was generally accepted to belong to the genus Hemitragus along with the Himalayan tahr (Hemitragus jemlahicus) and Arabian tahr (Arabitragus jayakari). Today, however, most authors follow Ropiquet and Hassanin (2005), who assigned the three tahrs to three monophyletic genera on the basis of molecular data, with the Nilgiri tahr being allied with the genus Ovis. The Nilgiri tahr has no subspecies.

The Nilgiri tahr is the largest of the three "tahrs" (but see above). Males are significantly heavier than females, with a body weights up to twice as much - 100 kg for males versus 50 kg for females.

The pelage of the Nilgiri tahr is short and smooth, likely as an adaptation to the wet climate this species inhabits (Prater, 1971; Rice, 1990). There is significant dimorphism between mature males and females. Females and immature males are an overall yellowish-brown to grey, with the underparts being paler (Lydekker, 1913; Prater, 1971; Rice, 1988; Nowak, 1991). The only significant marking in females is a dark stripe which runs down the dorsal midline (Lydekker, 1913). As males age, their pelage darkens to a deep chocolate or even blackish-brown - a process which begins at two years of age and takes over four years to complete (Lydekker, 1913; Prater, 1971; Rice, 1988). As this occurs, the shoulders, neck, and legs turn nearly black, with white knee-spots marking the anterior surface of the front legs (Rice, 1990). A distinctive silvery saddle-patch marks the back of mature male Nilgiri tahr, starting out as an indistinct pale tan area at five years of age and becoming paler and more defined until around eight years (Lydekker, 1913; Prater, 1971; Rice, 1988). Females have two nipples (Nowak, 1991).

The face of female Nilgiri tahr is the same color as the body and has no distinctive markings. In mature males, the face is nearly black and strikingly marked (Lydekker, 1913; Rice, 1990). A fawn-colored ring encircles the eye, with a similarly-colored patch behind each eye (Lydekker, 1913). In addition, a silvery stripe on each side of the face runs from in front of the eye towards the muzzle, much like the dark facial stripes seen in gazelles (Lydekker, 1913). There is no beard present in either sex (Nowak, 1991).

Both sexes of H. hylocrius bear relatively short, curving horns. Arising very close to each other at the top of the skull, the horns rise nearly parallel before diverging and curling downward (Prater, 1971). Their front surface (along the outer curve) is highly convex and has deeply transverse wrinkles, while the inner surface is almost flat (Lydekker, 1913; Prater, 1971). The horns lack the ridged keel seen in Himalayan tahr (Prater, 1971). Record horn length in males is 44.5 cm, with a girth of 25.1 cm (Lydekker, 1913; Prater, 1971). The horns of females are shorter and more slender, typically up to 30 cm in length, with a maximum recorded horn length of 35.6 cm (Prater, 1971; Rice, 1988).

The main breeding season (rut) of wild Nilgiri tahr is from June to August during the monsoons (Rice, 1990; Robinson, 2005). There is a corresponding peak in births in the cool, clear weather of January and February, although young may be born throughout the year (Prater, 1971; Rice, 1990; Robinson, 2005). Captive births at the Memphis Zoo were not seasonal, although males were most aggressive between September and November (Wilson, 1980). A single kid (rarely two) is born after a gestation period which lasts 178 to 190 days (see Prater, 1971; Wilson, 1980; Rice, 1990; Robinson, 2005). Females are highly protective of their offspring and will adopt threatening postures if other herd members approach too closely (Wilson, 1980).

For the first few weeks of life the infant lies hidden while the mother forages, but by two months of age the kid follows its mother (Wilson, 1980). Young may begin tasting solid food as early as two weeks of age, although they are not weaned until four (or sometimes six) months (Wilson, 1980; Rice, 1990). Sexual maturity in the wild is usually reached around three years of age, although in captivity females may produce their first offspring as early as 22 months of age, indicating sexual maturity at 16 months or younger (Wilson, 1980; Rice, 1990). Captive females are capable of breeding and producing offspring every 7-10 months (Wilson, 1980). Average life expectancy for Nilgiri tahr in the wild is estimated to be only three or 3.5 years, although the potential life span is at least 9 years (Rice, 1988; Rice, 1990).

Nilgiri tahr inhabit montane grasslands in southern India at elevations of 1,200-2,600 m above sea level (Rice, 1990; Mishra and Johnsingh, 1998; Kannery, 2002; Robinson, 2005). The climate of the region is very wet, with approximately four meters of precipitation falling every year (Rice, 1990). In the Anamalai Hills, Mishra and Johnsingh (1998) observed a habitat preference involving areas dominated by short meadows, although the tall grass species Cymbopogon exuosus was present in all the sites studied. Major short grass species in Nilgiri tahr habitat included Heteropogon contortus, Themeda triandra, and Chrysopogon aciculatus (Mishra and Johnsingh, 1998). Tahr observed in the neighbouring Eravikulam National Park were found in two principal grassland communities, one dominated by Eulalia phaeothrix and Ischaemum indicum and the other by Andropogon polyptichus, both with similar vegetative cover but with forbs in higher abundance in the latter (Rice, 1988). In all cases, the meadows used by tahr are typically above the forest line and adjacent to rocky crags which are used for shelter and as a refuge when threatened (Prater, 1971; Rice, 1990). Indeed, Rice (1988) suggests that grazing habitat for Nilgiri tahr is limited by the availability of cliffs (escape terrain), and not by appropriate food species. At lower elevations, the grasslands are replaced by stunted evergreen forests known locally as "sholas", which are typically avoided by tahr (Rice, 1988; Robinson, 2005).

In the wild, Nilgiri tahr are preyed upon by leopard (Panthera pardus) and dhole (Cuon alpinus), while a large number are also taken by humans (Rice, 1988; Rice,. 1990). Prater (1971) alone adds the tiger (Panthera tigris) to this list of predators. When threatened, tahr flee to inaccessible terrain in the crags above the grazing meadows. As with most caprines, they are extremely quick and sure-footed over precipitous ground (Prater, 1971).

H. hylocrius is a grazer, feeding on herbs and grasses (Rice, 1990; Robinson, 2005).

Nilgiri tahr are active from dawn to late evening, grazing most frequently in the early morning and late afternoon (Prater, 1971; Nowak, 1991). When the sun is at its peak, tahr retreat to higher, rockier terrain in order to rest in the relatively secure shade of cliffs (Prater, 1971). While the herd rests, at least one member (usually a female) remains alert, serving as a sentinel and watching for predators (Prater, 1971; Wilson, 1980). These animals are sharp-sighted and able to spot danger approaching from below at a distance, but are less aware of danger descending from above (Prater, 1971). Alarm is sounded as a whistle or snort (Wilson, 1980).

The social system of the Nilgiri tahr is rather flexible. Animals may associate in groups as small as six animals or as large as 150, but typically a herd contains 11-71 individuals (Prater, 1971; Robinson, 2005). In Eravikulam National Park, the average herd size observed by Rice (1990) was 42 individuals. Mixed herds are common, as are all-male groups and maternal herds composed of adult females and their young (Robinson, 2005). Old males associate in larger mixed herds during the breeding season, but are often solitary or in small all-male groups at other times of the year, especially the hot season (Prater, 1971; Rice, 1990). While female herds typically inhabit particular home ranges, adult males will move between these groups (Rice, 1990). The sex ratio of the wild population is skewed towards females, with an average of 59.7 (range of 53.7 to 66.7) males for every 100 females; adult females also make up a large proportion (40-45%) of the total population (Rice, 1988).

When mature males join female herds during the rut, a dominance hierarchy evolves based on size and age (Rice, 1990). If two males are evenly matched, a fight will develop, but not before a ritualized pre-fight display, in which males will lower their heads, arch their backs, and walk with a stiff-legged gait (Wilson, 1980). Several fighting positions have been recorded between rival males: standing side by side, both facing the same direction, and knocking the sides of the horns together; crashing their horns head-on; or standing parallel but facing opposite directions, and ramming the shoulders and flanks of the rival with their horns (Wilson, 1980; Rice, 1990). This last posture can be extremely dangerous, as the sharp tips of the horns can cause extensive damage when hooked sharply upwards; these fights can end in death (Wilson, 1980). When engaged in combat, males can be oblivious to their immediate surroundings - as they spin around each other, they usually travel downhill and will continue to fight even if they leave the upland grassland and enter the sholas below (Rice, 1988). The loser of any male-male conflict is typically driven from the group, although they may return and be tolerated if they defer to the dominant animal (Rice, 1990).

The Nilgiri tahr is endemic to the Western Ghats mountain range in India, straddling the border between the states of Kerala and Tamil Nadu (Rice, 1990; Fox and Johnsingh, 1997).

Countries: India (Alempath and Rice, 2008).

The IUCN Caprinae Specialist Group classifies the Nilgiri tahr as endangered (Alempath and Rice, 2008), but it does not appear on any CITES appendix. The present population is estimated to be 1,800-2,000 mature individuals; current trends indicate that these numbers are in decline (Alempath and Rice, 2008). Nilgiri tahr exist only in small, isolated populations due to extreme habitat fragmentation and are thus vulnerable to local extinction (Fox and Johnsingh, 1997; Alempath and Rice, 2008). While Eravikulam National Park supports approximately 760 individuals, only one other area, the Grass Hills in Anamalai, maintains a population of more than 250 animals (Fox and Johnsingh, 1997; Kannery, 2002; Alempath and Rice, 2008). As an endemic species, N. hylocrius receives full (legal) protection under the Indian Wildlife Act of 1972 - unfortunately this protection is rarely enforced and illegal hunting is a major threat (Fox and Johnsingh, 1997; Kannery, 2002; Alempath and Rice, 2008).

The many facets of habitat loss are another principal threat to the continued survival of the Nilgiri tahr. Overgrazing by domestic livestock increases competition and reduces available forage (and thus the number of tahr which can survive in a given area), but also allows for the invasion of graze-resistant weedy species into meadows, causing further decline in the grasses which tahr feed upon (Mishra and Johnsingh, 1998). Compounding this problem, the grassland habitat of the tahr continues to be converted into agricultural land, with the result that the present distribution of H. hylocrius is about one-tenth of its historical range (Mishra and Johnsingh, 1998; Kannery, 2002; Alempath and Rice, 2008). Inbreeding (a result of such small, isolated populations) may prove to be a future concern to the survival of the Nilgiri tahr (Kannery, 2002).

Nilgiri is an Indian word meaning "Blue Hills" - these tahr are found in Nilgiri District in Tamil Nadu State. Thar is a Nepalese name for the Himalayan tahr (Hemitragus jemlahicus), which was once thought to be closely related to this species.

Hemitragus is derived from the Greek hemi (half) and tragos (a goat) - tahr have many characters in common with true goats (Capra), but lack a beard and have several other unique features. The species name hylocrius translates as "goat of the woods", from the Greek words hule, meaning a wood or forest, and krios, which translates as a sheep or ram.

Local names

Varai ádoo, Varayadu [Tamil and Kanarese] (Prater, 1971; Kannery, 2002)

Mulla átu [Malayalam] (Prater, 1971)

 

French

Tahr des monts Nilgiri (Rice, 1990)

 

German

Nilgiritahr (Rice, 1990)