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The Himalayan tahr (Hemitragus jemlahicus), or the common tahr, is a large ungulate related to the wild goat and the only  extant member of the genus Hemitragus. The Himalayan tahr is native to the Himalayas in  Southern Tibet,  Northern India, and  Nepal. The Himalayan tahr has been introduced as an alien species to New Zealand, parts of  South America, and  South Africa. Efforts in each of these regions are being made to control the Himalayan tahr population and to reduce its impact on the native ecosystem.

Taxonomy and Etymology
The word Tahr comes from the nepali language and was first used in English writing in 1835. Tahrs belong to the order  Artiodactyla, which denotes an even-toed ungulate  mammal. Close relatives to the Himalayan Tahr also associated to the  Caprinae subfamily include sheep and  goats.

General
The Himalayan tahr have small heads, small pointed ears, large eyes, and horns that vary between males and females. Their horns reach a maximum length of 46 centimeters. Himalayan tahrs are sexually dimorphic, with females being smaller in weight and in size and having smaller horns. The horn is curved backwards, preventing injury during mating season when headbutting is a common mating ritual among males. The average Tahr usually weighs between 300 to 400 pounds (135 to 180 kilograms) and is shorter in height than in length. The exterior of a tahr is well adapted to the harsh climate of the Himalayans. They sport a thick, reddish wool coat and a thick undercoat, indicative of the conditions of their habitat. This coat thins with the end of winter and becomes lighter in color. This shedding is presumably an adaptation that allows their internal  body temperatures to adjust to the harsh temperatures of the  Himalayan Mountains

As members of the ungulate  group of mammals, the Himalayan tahr possess an even number of toes. They have adapted the unique ability to grasp both smooth and rough surfaces that are typical of the mountainous terrain on which they preside. This useful characteristic also helps their mobility, which is discussed later in  Impact as an invasive species section. The hooves of the tahr have a rubber-like core which allows for gripping smooth rocks while keratin at the rim of their hooves allow increase the hoof durability, which is important for traversing the rocky ground typical of the mountainous terrain on which they preside (see  Intraspecific Competition below). This adaptation allows for confident and swift maneuvering of the terrain.

The average lifespan of a Himalayan Tahr typically ranges between 14 and 15 years of age, with females living longer than males. The oldest lived Himalayan tahr was 22 years old in captivity.

Reproduction
Tahr are polygynous, and males are subject to stiff competition for access to females. Young reproductive males roam and mate opportunistically (when larger males aren’t present) while more mature males (>4 years) will engage in ritualistic behavior  and fighting to secure mates. During mating season, reproductive males lose much of their fat reserves, while females and non-reproductive males do not, indicating that there is a substantial cost to these behaviors. Factors that contribute to which males dominate include size, weight, and testosterone levels. Interestingly, it has also been demonstrated that coat color can have an affect; Himalayan tahr with lighter coats are more likely to gain access to estrus females Himalayan Tahr have precocious young which can stand soon after birth. Females have been observed to have a gestation period of 180-242 days, usually with a  litter size of only one kid. This indicates that sexual selection can be extremely important to the fitness of males, which is discussed further in the  Intraspecific competition section below.

Diet
The herbivorous diet of the Himalayan tahr leave them spending most of their time browsing grasses, leaves, and some fruits. The short legs of Tahr allow them to balance while reaching for the leaves of shrubs and small trees. Research indicates that the tahr consume more woody plants than herb species with as much as 75% of the tahr diet consisting of natural grasses. The Tahr, like most members of the bovid family, are  ruminants and have complex  digestive systems. A multi-chambered stomach allows the Tahr to repeatedly regurgitate their food, chew it, and obtain nutrients from otherwise indigestible plant tissues. This adaptation is discussed further below.

Fundamental niche
The Himalayan tahr is adapted to life in a cool climate with rocky terrain, which allows them to be found in mountainous areas. In the Himalayas, they are mainly found on slopes ranging from 2,500 to 5,000 meters. Himalayan tahr can eat a wide variety of plants, discussed above in the diet section. They most often inhabit locations in where vegetation is exposed for browsing and grazing. During the winter (when snow covers vegetation at higher elevations), they are found on slopes that are lower in altitude.

Intraspecific competition
During the rut, male Himalayan tahrs often compete with other males for access to females. Factors that contribute to reproductive success include high weight, large body size, large horn size, and high aggression. It has also been observed that lighter coat color is a factor that determines rank among Himalayan tahrs, and that male Himalayan tahr with light coats will mate more often. In addition, the horns of the male are often used in the ritual process in order to court female tahrs (either for display purposes or, less often, for direct combat), although these horns can also serve as a defense mechanisms against potential predators.

Interspecific competition
Other ungulate herbivores with overlapping natural  ranges include  bharal,  argali, and  goral. Removal experiments (experiments in which one of the hypothesized competitors is removed, and the affect on the other species is observed) have not been conducted to determine empirically that competition is actually occurring, but the animals do share food resources. Competition can occur when two or more species share a limited resource, such as particular food sources, in a given area. Since the Himalayan tahr and the other ungulates are eating the same foods, it is possible that competition is occurring among them.

Predation
Tahr are predated upon by Himalayan snow leopard. The snow leopards also eat the other ungulate species in the area, which could result in apparent competition between the Himalayan tahr and one or more of the other herbivores. Apparent competition can occur when two species share a predator. If an increase in one of the prey species increases the predator population, this can translate into increased predation on the other prey species. This is called apparent competition, because the effect was indirect from the two prey species via the predator species rather than by direct competition of the two prey species for some shared resource.

Argentina
The tahr was recently introduced to Argentina in 2006 by private individuals, presumably for hunting purposes. The implantation has been deemed successful, but it is too soon to determine whether it will be detrimental to the environment. The future of the tahr as an alien species is still unknown in Argentina.

New Zealand
The tahr was first introduced to New Zealand for sport and have since expanded rapidly into neighboring areas. They currently occupy a portion of the Southern Alps and are still being hunted as a sport in New Zealand.

South Africa
The Himalayan tahr was introduced to South Africa when, in the 1930’s, two Himalayan Tahrs escaped from a zoo. Subsequent populations of tahr have descended from the original escaped pair. Most of the population has been culled to make way for the reintroduction of the indigenous  antelope, the klipspringer.

Success as an invasive species
A key factor contributing to the success of the Himalayan tahr as an invasive species is their mobility. During the nighttime they move to locations with lower elevations in order to have better access to resources such as food and water, whereas during the daytime they move to locations with higher elevation in order to rest and avoid predators. This mobile behavior not only allows them to seek refuge from predators but also allows them to have access to resources over a large area.

Another key characteristic that allows Himalayan tahr to be successful as an invasive species is their digestive tract (see  Diet above). Their digestive system allows them to consume a wide variety of vegetation ranging from easy to digest leaves/grasses to woody shrubs and other “tough” vegetation that is not as easily digested by other species. This flexibility in diet not only allows Himalayan tahr to have a competitive advantage for resource use in their environment among other species, but it also allows them to be less hindered by abiotic disruptions and other natural disasters. In other words, their ability to digest a large range of vegetation allows the Himalayan tahr to have a bigger fundamental niche and as a result increase their success as a invasive species.

Lastly, the Himalayan tahr lacks predators in the regions where it has been introduced, and therefore is only limited by access to food and water, and its own reproductive rate.

Impact as an invasive species
A negative impact the Himalayan tahr has on their environment is increased herbivory on the native vegetation of the ecosystem, which can make it harder for other herbivores to find food. The increased herbivory can also lead to a decrease in soil nutrients, such as oxygen, nitrates, and ammonia, resulting in  positive feedback loop, making it harder for plants to grow at all. Consequently, the natural fauna of the ecosystem is heavily affected. For example, it was observed that endangered camelids were forced to adapt and move to higher elevations due to the increased herbivory from the Himalayan tahr. This increase in herbivory has also resulted in poor soil quality in many environments occupied by the Himalayan tahr and has severely limited the presence of certain plant species. The lack of certain vegetation, in turn, may affect animal species that rely on them as a food source.

Data on the rapid expansion of the tahr are documented by government agencies. Through a time span of 16 years, the Himalayan tahr reached up to 33 tahr/km2 in New Zealand - twice the initial population (2*N0). Without regulated hunting or the presence of natural barriers, the Himalayan tahr can pose a large threat to the indigenous fauna and flora populations within the area.

Control Methods
In 1930, the tahr was denied protection by the Animals Protection and Game Act (1921-22) and was thus recognized as a danger to the environment (although the species is still considered to be endangered in the Himalayas by the World Conservation Union ). Since 1937, various government operations have been undertaken to reduce tahr population and/or keep it at fixed numbers. The control of tahr remains ecologically and economically significant because of their widespread destruction of native flora and fauna and their valuable capture for hunters, respectively.

Control by hunting
In 1933, New Zealand’s Department of Conservation prepared the Himalayan Tahr Control Plan which lists “aerial game recovery operations, recreational and safari hunting as primary means of control”. Under the plan, the area of the tahr distribution was divided into two exclusion zones and seven management units. The exclusion zones set boundaries on the area that the tahr inhabits, with the official control operations to be employed to prevent tahr from spreading beyond those zones. The management unit has a fixed maximum tahr density, which varies from 1-2.5 tahr/km2 and is considered to be low enough to have a minimal negative impact on the ecosystem and, even, restore native vegetation. Under these conditions, the plan aimed to keep tahr numbers below 10,000 throughout the South Island. Since then, New Zealand’s Department of Conservation (DOC) has been actively advertising tahr hunting and has created 59 tahr hunting areas. Hunting remains primary means of control of the invasive species: government operations have killed more than 24,000 tahrs by shooting since 1933. Hunting remains the primary means of control of this invasive species with government operations having killed more than 24,000 tahrs by shooting since 1933. As a primary method of tahr population control (although one that is hard to quantify), hunting seems to be an efficient strategy because a large number of people take part in it. In general, hunting is a good method of biological control because it has a direct impact on tahr population and minimal indirect consequences on the surrounding ecology.

Control by poisoning
In 1960, sodium monofluoroacetate (also known as compound 1080) was used to poison tahrs. This compound is a derivative of fluoroacetic acid and is commonly used in many countries such as Mexico, Australia, The United States, and  New Zealand as a pesticide. Compound 1080 is highly water-soluble and is diluted by rainwater and broken down by aquatic microorganisms. Water samples after baiting operations did not reveal dangerous levels of the compound. In the soil, sodium monofluoroacetate is converted by bacteria and fungi to metabolic product, shown to be nonhazardous to the environment.

According to Australia’s Department of Primary Industries, Parks, Water, and Environment, mammals (particularly cats and dogs) are the most susceptible to compound 1080 poisoning. Fish, birds, and amphibians generally are highly tolerant to the poison. Although compound 1080 is a strong enough pesticide to eradicate the entire tahr population, political pressures from hunter groups hinder its use. Opposition by the general public also contributes to the decreased use of 1080 with concerns that the accumulation of 1080 at higher levels of the food chain will pose danger to mammals such as dogs, deer and pigs.

Current control method
The success of the Tahr Control Plan as well as the future of tahr in New Zealand can be seen from the report prepared by Kenneth F.D. Hughey and Karen M. Wason, which presents survey results conducted among farmers living within tahr distribution. As they demonstrate, roughly 80% of farmers view tahrs as a resource, not as a threat. The respondents indicated that they place conservational and commercial value (live animal/meat, hunting, farming) on tahr. Thirty six percent of these farmers also reported to having earned at least $1,000 a year in profit from having tahr on their property, with the highest earnings being above $50,000 (Table 5.5 of that study), usually as a result of allowing professionally guided hunters on their property. Also, a 1988 study showed that hunters spent $851 per person per year on hunting with expenses being greatest for big-game targets, such as the Himalayan Tahr. The fact that the tahr is no longer viewed by general public as an unwanted species may indicate that the tahr numbers are now successfully reduced to an acceptable range. This reflects the Department of Conservation’s efforts to promote tahr hunting, consistent monitoring for the trends in tahr population, and official control operations. It is estimated that, in New Zealand alone, $840M has been spent on alien species per year (.9% of GNP), 25% being towards vertebrate mammals. Of these total costs, $400 M has been dedicated to defense against the invasive species. If conditions maintain, “the total cost of alien vertebrates in New Zealand may therefore exceed $270 million per year”. However, as shown above, these costs may come along with some negative environmental effects on native ecosystems.