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There are nine subspecies of tiger, three of which are extinct and one of which is almost certain to become extinct in the near future. Their historical range (severely diminished today) ran through Russia, Siberia, Iran, Afghanistan, India, China and south-east Asia, including the Indonesian islands. The South China Tiger is believed to be the first tiger. These are the surviving subspecies, in descending order of wild population:

The Bengal tiger or the Royal Bengal tiger

is found in parts of India, Bangladesh, Nepal, Bhutan, and Burma. It lives in varied habitats – grasslands, subtropical and tropical rainforests, scrub forests, wet and dry deciduous forests and mangroves. The Indian government’s estimated population figure for these tigers is between 3,100 and 4,500, 3,000 of which are found in India alone. However, many Indian tiger conservationists doubt this number, seeing it as overly optimistic.
The number of Bengal tigers in India may be lower than 2000, as most of the collected statistics are based on pugmark identification, which often gives a biased result. Even though this is the most ‘common’ tiger, these tigers are under severe pressure from both habitat destruction and poaching.

In 1972, India launched a massive wildlife conservation project, known as Project Tiger, to protect the depleting numbers of tigers in India. The project helped increase the population of these tigers from 1,200 in the 1970s to 3,000 in the 1990s and is considered as one of the most successful wildlife conservation programs. At least one Tiger Reserve (Sariska) has lost its entire tiger population to poaching. Male Bengal tigers can range anywhere from 200 to 295 kg (440-650 lb) and females range between 120-180 kg (264-400 lb). Most males in the wild usually weigh 205 to 227 kg (450-500 lb), while the average female will weigh about 140 kg (310 lb). However, there are recorded instances of shot males that weighed more than 300 kg. One large male killed in Nepal in 1942 weighed 318 kg (701 lbs), while another, killed in 1910 in India, weighed 317 kg (699 lbs).

The largest Bengal tiger ever shot was a male 3.3 m in total length and weighed close to 390 kg (858 lb.); this giant was killed in 1967.

The Indochinese tiger

is found in Cambodia, China, Laos, Burma, Thailand, and Vietnam. Estimates of its population vary between 1,200 to 1,800, but it seems likely that the number is in the lower part of the range. The largest current population is in Malaysia, where illegal poaching is strictly controlled, but all existing populations are at extreme risk from habitat fragmentation and inbreeding. In Vietnam, almost three-quarters of the tigers killed provide stock for Chinese pharmacies. Also, the tigers are seen by poor natives as a resource through which they can ease poverty. Indochinese tigers are smaller and darker than Bengal tigers. Males weigh from 150-190 kg on average while females are smaller at 110-140 kg.

The Malayan tiger

exclusively found in the southern (Malaysian) part of the Malay Peninsula, was not considered a subspecies in its own right until 2004. The new classification came about after a study by Luo et al. from the Laboratory of Genomic Diversity Study, [9] part of the National Cancer Institute of the United States. Recent counts showed there are 600-800 tigers in the wild, making it the third largest tiger population behind the Bengal tiger and the Indochinese tiger. The Malayan tiger is a national icon in Malaysia, appearing on its coat of arms and in logos of Malaysian institutions, such as Maybank.

The Maltese Tiger (Blue Tiger)

The Sumatran tiger

is found only on the Indonesian island of Sumatra. The wild population is estimated at between 400 and 500, seen predominantly in the island’s five national parks. Recent genetic testing has revealed the presence of unique genetic markers, indicating that it may develop into a separate species, if it is not made extinct. This has led to suggestions that Sumatran tigers should have greater priority for conservation than any other subspecies. Habitat destruction is the main threat to the existing tiger population (logging continues even in the supposedly protected national parks), but 66 tigers were recorded as being shot and killed between 1998 and 2000, or nearly 20% of the total population.
The Sumatran tiger is the smallest of all living tiger subspecies. Adult males weigh between 100-130 kg, females 70-90 kg. Their small size is an adaptation to the thick, dense forests of the Sumatra island where they reside, as well as the smaller-sized prey. On February 3, 2007 a pregnant Sumatran Tiger was caught by people from Rokan Hilir village at Riau province. Indonesian fauna conservation officials are planning to transfer her to the Bogor Safari Park in Java.

The Amur tiger (Siberian Tiger)

also known as the Siberian, Manchurian or North China tiger, is confined almost completely to Siberia, where it is now protected. The last two censuses(1996 and 2005) found 450-500 Siberian tigers within their single and more or less continuous range making it one of the biggest undivided tiger populations in the world.
Considered the largest subspecies, the largest wild Siberian tiger on record weighed 384 kg (845 lb.), while two captive ones weighed 465kg (1025lb) and 423 kg (932 lb.) respectively. Some Bengal tigers grow to the same length as Siberian tigers, but they are less stocky. Weights can vary substantially depending on whether the tiger has been fully fed or has an empty belly. The average weight of a male Siberian tiger is around 227 kg (500 lb), but they can be anywhere from 205 to 364 kg (450-800 lb). The Siberian tiger is also noted for its thick coat, distinguished by a paler golden hue and a smaller number of stripes. The Siberian tiger is the largest and heaviest of all living felines. A six-month old Siberian tiger can be as big as a fully grown leopard.

The South China Tiger

also known as the Amoy or Xiamen tiger, is the most critically endangered subspecies of tiger and will almost certainly become extinct. It is also considered to be the first of all tiger subspecies. This subspecies is one of the smallest tiger species. The length of the South China tiger ranges from 2.2-2.6 m (87-104 inches) for both males and females. Males weigh between 127 and 177 kg (280-390 lb.) while females weigh between 100 and 118 kg (220-260 lb.). It seems likely that the last known wild South China tiger was shot and killed in 1994, and no live tigers have been seen in their natural habitat for the last 20 years. In 1977, the Chinese government passed a law banning the killing of wild tigers, but this appears to have been too late to save the subspecies.
There are currently 59 known captive South China tigers, all within China, but these are known to be descended from only six animals. Thus, the genetic diversity required to maintain the subspecies no longer exists, making its eventual extinction very likely. Currently, there are breeding efforts to reintroduce these tigers to the wild by 2008.