 Hemitragus
hylocrius
Nilgiri tahr |
Taxonomy | Description
| Reproduction | Ecology
| Behavior | Distribution
| Conservation | Remarks
| Literature |
| Taxonomy
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Hemitragus hylocrius [Ogilby, 1838].
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Citation: Proc. Zool. Soc. Lond., 1837:81 [1838].
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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). The Nilgiri tahr is generally accepted as a full
species, although some authors have placed it as a subspecies of the
Himalayan tahr, Hemitragus
jemlahicus (see Nowak, 1991; Wilson and Reeder, 1993). However,
genetic evidence presents a strong case that the Nilgiri tahr is a species
unto itself (see Bernischke and Kumamoto, 1980). The Nilgiri tahr has
no subspecies (i.e., it is monotypic). The only invalid synonym for
H. hylocrius is H. warryato (after the Tamil name for this
species; see "Remarks" below).
General Characteristics
The Nilgiri tahr is the largest of the three tahr species, being just slightly
larger than the Himalayan tahr,
H. jemlahicus (Prater, 1971). Males are significantly heavier
than females, with a body weights up to twice as much - 100 kg for males
versus 50 kg for females.
Reported measurements for Nilgiri tahr (Hemitragus hylocrius) |
| Source |
Adult Weight |
Head & Body Length |
Shoulder Height
|
Tail Length |
| Lydekker, 1913 |
- |
- |
99-107 cm |
- |
Nowak, 1991
for Hemitragus |
50-100 kg |
90-140 cm |
61-106 cm |
9-12 cm |
| Prater, 1971 |
- |
- |
100-110 cm |
- |
| Rice, 1990 |
100 kg 
50 kg  |
150 cm
110 cm |
110 cm
80 cm |
10-15 cm |
| Robinson, 2005 |
80-100 kg
50 kg |
- |
- |
- |
| Wilson, 1980 |
101.8 kg
53.4 kg |
- |
- |
- |
Unlike the Himalayan tahr, the coat of the Nilgiri tahr is short -
probably 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 on the coat 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
light tan area at five years of age and becoming lighter and more defined
until around eight years (Lydekker, 1913; Prater, 1971; Rice, 1988).
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 side of
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). Females have two nipples,
unlike the two other species of tahr which have four (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). The 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 slenderer, typically up to 30 cm although the maximum recorded
horn length is 35.6 cm (Prater, 1971; Rice, 1988).
Ontogeny and Reproduction
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 seen 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). (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).
Ecology and Behavior
Nilgiri tahr inhabit montane grasslands 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 preference for areas
dominated by short meadows, although the tall grass species Cymbopogon
exuosus was present in all the sites studied. Major short grass
species 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 lschaemum 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).
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 is 42 individuals (Rice,
1990). 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 of the animal involved (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).
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. 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).
Genetics
Nilgiri tahr have a karyotype of 2n=58, of which only one chromosome is
metacentric; the entire karyotype is presented in Bernischke and Kumamoto
(1980).
Distribution
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 (IUCN, 2004).
Range Map (Redrawn from Fox and Johnsingh, 1997)
Conservation Status
The IUCN Caprinae Specialist Group classifies the Nilgiri tahr as endangered
(2004), but it does not appear on any CITES appendix. The present
population is estimated to be between 2,000 and 2,500 individuals; current
trends indicate that these numbers are in decline (Fox and Johnsingh,
1997). Nilgiri tahr exist only in small, isolated populations due to
extreme habitat fragmentation and are thus vulnerable to local
extinction (Fox and Johnsingh, 1997; IUCN, 2004). While Eravikulam
National Park supports nearly 1,000 individuals, only one other area, the
Grass Hills in Anamalai, maintains a population of more than 300 animals
(Fox and Johnsingh, 1997; Kannery, 2002). As an endemic species, H.
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; IUCN,
2004).
The many facets of habitat loss are another big 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; IUCN, 2004). Inbreeding (a result
of such small, isolated populations) may prove to be a future concern to
the survival of the Nilgiri tahr (Kannery, 2002).
Remarks
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 closely related Himalayan tahr (Hemitragus jemlahicus).
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.
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Local names
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Varai ádoo, Varayadu [Tamil and Kanarese] (Prater, 1971; Kannery,
2002)
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Mulla átu [Malayalam] (Prater, 1971)
-
-
French
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Tahr des monts Nilgiri (Rice, 1990)
-
-
German
-
Nilgiritahr (Rice, 1990)
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