Bengal Tiger

Bengal-Tiger---Panthera-Tigris-Tigris

Bengal Tiger (Panthera Tigris Tigris)

The Bengal tiger (Panthera tigris tigris) is the most numerous tiger subspecies. Its populations have been estimated at 1,706–1,909 in India, 440 in Bangladesh, 163–253 in Nepal and 67–81 in Bhutan.[2][3][4][5] Since 2010, it has been classified as endangered by the IUCN. The total population is estimated at fewer than 2,500 individuals with a decreasing trend, and none of the Tiger Conservation Landscapes within the Bengal tiger’s range is large enough to support an effective population size of 250 adult individuals.[1]

Bengal is traditionally fixed as the typical locality for the binomen Panthera tigris, to which the British taxonomist Reginald Innes Pocock subordinated the Bengal tiger in 1929 under the trinomen Panthera tigris tigris.[6]

It is the national animal of both India and Bangladesh.[7]

Characteristics

The Bengal tiger’s coat is yellow to light orange, with stripes ranging from dark brown to black; the belly and the interior parts of the limbs are white, and the tail is orange with black rings. The white tiger is a recessive mutant of the Bengal tiger, which is reported in the wild from time to time in AssamBengalBihar and especially from the former State of Rewa. However, it is not to be mistaken as an occurrence of albinism. In fact, there is only one fully authenticated case of a true albino tiger, and none of black tigers, with the possible exception of one dead specimen examined in Chittagong in 1846.[11]

Male Bengal tigers have an average total length of 270 to 310 cm (110 to 120 in) including the tail, while females measure 240 to 265 cm (94 to 104 in) on average.[12] The tail is typically 85 to 110 cm (33 to 43 in) long, and on average, tigers are 90 to 110 cm (35 to 43 in) in height at the shoulders.[13] The weight of males ranges from 180 to 258 kg (397 to 569 lb), while that of the females ranges from 100 to 160 kg (220 to 350 lb).[12] The smallest recorded weights for Bengal tigers are from the Bangladesh Sundarbans, where adult females are 75 to 80 kg (165 to 176 lb).[14] Bengal tigers have exceptionally stout teeth, and the canines are the longest among all living felids; measuring from 7.5 to 10 cm (3.0 to 3.9 in) in length.[15]

Records

Two tigers shot in Kumaon and near Oude at the end of the 19th century allegedly measured more than 12 ft (370 cm). But at the time, sportsmen had not yet adopted a standard system of measurement; some would measure between pegs while others would round the curves.[16]

In the beginning of the 20th century, a male Bengal tiger was shot in central India with a head and body length of 221 cm (87 in) between pegs, a chest girth of 150 cm (59 in), a shoulder height of 109 cm (43 in) and a tail length of 81 cm (32 in), which was perhaps bitten off by a rival male. This specimen could not be weighed, but it was calculated to weigh no less than 272 kg (600 lb).[17]

A heavy male weighing 570 lb (260 kg) was shot in northern India in the 1930s.[18] However, the heaviest known tiger was a huge male killed in 1967 that weighed 388.7 kg (857 lb) and measured 322 cm (127 in) in total length between pegs, and 338 cm (133 in) over curves. This specimen is on exhibition in the Mammals Hall of the Smithsonian Institution.[19] In 1980 and 1984, scientists captured and tagged two male tigers in Chitwan National Park that weighed more than 270 kg (600 lb).[20]

Genetic ancestry

Bengal tigers are defined by three distinct mitochondrial nucleotide sites and 12 unique microsatellite alleles. The pattern of genetic variation in the Bengal tiger corresponds to the premise that they arrived in India approximately 12,000 years ago.[21] This is consistent with the lack of tiger fossils from the Indian subcontinent prior to the late Pleistocene and the absence of tigers from Sri Lanka, which was separated from the subcontinent by rising sea levels in the early Holocene.[22]

Body weight

Bengal tigers may weigh up to 325 kg (717 lb) and reach a head and body length of 320 cm (130 in).[15] Several scientists indicated that adult male Bengal tigers from Nepal, Bhutan, and Assam, Uttarakhand and West Bengal in northern India (collectively, the tigers of the Terai) consistently attain more than 227 kg (500 lb) of body weight. Seven adult males captured in Chitwan National Park in the early 1970s had an average weight of 235 kg (518 lb) ranging from 200 to 261 kg (441 to 575 lb), and that of the females was 140 kg (310 lb) ranging from 116 to 164 kg (256 to 362 lb).[23] Males from northern India are nearly as large as Siberian tigers with a greatest length of skull of 332 to 376 mm (13.1 to 14.8 in).[24]

Three males captured in Nagarahole National Park in India had a head and body length which ranged from 189 to 204 cm (74 to 80 in), with a tail length of 100 to 107 cm (39 to 42 in), while a single female measured 161 cm (63 in), with a tail length of 87 cm (34 in). Adult male Bengal tigers in Nagarahole National Park ranged from 230 to 260 kg (510 to 570 lb) in weight. An adult male tiger named “T-03” that was killed by a large male gaur, weighed 257 kg (567 lb). Another male, “T-04” who was estimated to be between 3 and 4 years old weighed 250 kg (550 lb) and had a head and body length of 290 cm (110 in). “T-01” was an old male that weighed 231 kg (509 lb). A collared male weighed 240 kg (530 lb) despite the fact that both his canine teeth were broken. The tigresses in the area were equally massive. One female, named “Sundari” weighed 150 kg (330 lb). Another female, named “T-02”, had a head and body length of 250 cm (98 in) and weighed 177 kg (390 lb).[25]

In comparison, a weight range of 150 to 189 kg (331 to 417 lb) is considered fairly average for a male African lion in the Serengeti.[26][27]

Verifiable Sundarbans tiger weights are not found in any scientific literature. Forest Department records list weight measurements for these tigers, but none are verifiable and all are guesstimates. There are also reports of head and body lengths, some of which are listed as over 365.7 cm (144.0 in). More recently, researchers from the University of Minnesota and the Bangladesh Forest Department carried out a study for the US Fish and Wildlife Service and weighed three Sundarbans tigresses from Bangladesh. All three tigers were female, two of which were collared, captured and sedated, but the other one had been killed by local villagers. The two collared tigresses were weighed using 150 kg (330 lb) scales, and the tigress killed by villagers was weighed using a balance scale and weights. The two collared females both showed signs of teeth wear and both were between 12 and 14 years old. The tigress killed by the villagers was a young adult, probably between 3 and 4 years old, and she was likely a pre-territorial transient. The three tigresses had a mean weight of 76.7 kg (169 lb). One of the two older female’s weight 75 kg (165 lb) weighed slightly less than the mean because of her old age and relatively poor condition at the time of capture. Skulls and body weights of Sundarbans tigers were found to be distinct from other subspecies, indicating that they may have adapted to the unique conditions of the mangrove habitat. Their small sizes are probably due to a combination of intense intraspecific competition and small size of prey available to tigers in the Sundarbans, compared to the larger deer and other prey available to tigers in other parts.[28]

Distribution and habitat

In 1982, a sub-fossil right middle phalanx was found in a prehistoric midden near Kuruwita in Sri Lanka, which is dated to about 16,500 ybp and tentatively considered to be of a tiger. Tigers appear to have arrived in Sri Lanka during a pluvial period during which sea levels were depressed, evidently prior to the last glacial maximumabout 20,000 years ago.[29] In 1929, the British taxonomist Pocock assumed that tigers arrived in southern India too late to colonize Sri Lanka, which earlier had been connected to India by a land bridge.[9]

In the Indian subcontinent, tigers inhabit tropical moist evergreen foreststropical dry forests, tropical and subtropical moist deciduous forestsmangroves, subtropical and temperate upland forests, and alluvial grasslands. Latter tiger habitat once covered a huge swath of grassland and riverine and moist semi-deciduous forests along the major river system of the Gangetic and Brahmaputra plains, but has now been largely converted to agricultural land or severely degraded. Today, the best examples of this habitat type are limited to a few blocks at the base of the outer foothills of the Himalayas including the Tiger Conservation Units (TCUs) RajajiCorbettBardiaBanke, and the transboundary TCUs ChitwanParsaValmikiDudhwaKailali and Sukla PhantaKishanpur. Tiger densities in these TCUs are high, in part because of the extraordinary biomass of ungulate prey.[30]

The Bengal tigers in the Sundarbans in India and Bangladesh are the only tigers in the world inhabiting mangrove forests. The population in the Indian Sundarbans is estimated as 70 tigers in total.[2]

India

In the past, Indian censuses of wild tigers relied on the individual identification of footprints known as pug marks — a method that has been criticised as deficient and inaccurate, though now camera traps are being used in many places.[31]

Good tiger habitats in subtropical and temperate upland forests include the Tiger Conservation Units (TCUs) ManasNamdapha. TCUs in tropical dry forest include Hazaribagh National ParkNagarjunsagar-Srisailam Tiger ReserveKanhaIndravati corridor, Orissa dry forestsPanna National ParkMelghat Tiger Reserve and Ratapani Tiger Reserve. The TCUs in tropical moist deciduous forest are probably some of the most productive habitats for tigers and their prey, and include KazirangaMeghalayaKanhaPenchSimlipal and Indravati Tiger Reserves. The TCUs in tropical moist evergreen forests represent the less common tiger habitats, being largely limited to the upland areas and wetter parts of the Western Ghats, and include the Tiger Reserves of PeriyarKalakad-MundathuraiBandipur and Parambikulam Wildlife Sanctuary.[30]

During the tiger census of 2008, camera trap and sign surveys using GIS were employed to project site-specific densities of tigers, their co-predators and prey. Based on the result of these surveys, the total tiger population was estimated at 1,411 individuals ranging from 1,165 to 1,657 adult and sub-adult tigers of more than 1.5 years of age. Across India, six landscape complexes were surveyed that host tigers and have the potential to be connected. These landscapes comprise the following:[32]

In May 2008, forest officials spotted 14 tiger cubs in Rajasthan‘s Ranthambore National Park.[33] In June 2008, a tiger from Ranthambore was relocated to Sariska Tiger Reserve, where all tigers had fallen victim to poachers and human encroachments since 2005.[34]

As of 2014, adult and subadult tigers at 1.5 years or older are estimated to number 408 in Karnataka, 340 in Uttarakhand, 308 in Madhya Pradesh, 229 in Tamil Nadu, 190 in Maharashtra, 167 in Assam, 136 in Kerala, and 117 in Uttar Pradesh.[3]

Bangladesh

Tigers in Bangladesh are now relegated to the forests of the Sundarbans and the Chittagong Hill Tracts.[35] The Chittagong forest is contiguous with tiger habitat in India and Myanmar, but the tiger population is of unknown status.[36]

As of 2004, population estimates in Bangladesh ranged from 200 to 419, mostly in the Sunderbans.[35][37] This region is the only mangrove habitat in this bioregion, where tigers survive, swimming between islands in the delta to hunt prey.[30] Bangladesh’s Forest Department is raising mangrove plantations supplying forage for spotted deer. Since 2001, afforestation has continued on a small scale in newly accreted lands and islands of the Sundarbans.[6] From October 2005 to January 2007, the first camera-trap survey was conducted across six sites in the Bangladesh Sundarbans to estimate tiger population density. The average of these six sites provided an estimate of 3.7 tigers per 100 km2 (39 sq mi). Since the Bangladesh Sundarbans is an area of 5,770 km2 (2,230 sq mi) it was inferred that the total tiger population comprised approximately 200 individuals.[38] In another study, home ranges of adult female tigers were recorded comprising between 12 and 14 km2 (4.6 and 5.4 sq mi).,[39] which would indicate an approximate carrying capacity of 150 adult females.[40] The small home range of adult female tigers (and consequent high density of tigers) in this habitat type relative to other areas may be related to both the high density of prey and the small size of the Sundarbans tigers.[14]

Since 2007 tiger monitoring surveys have been carried out every year by WildTeam in the Bangladesh Sundarbans to monitor changes in the Bangladesh tiger population and assess the effectiveness of conservation actions. This survey measures changes in the frequency of tiger track sets along the sides of tidal waterways as an index of relative tiger abundance across the Sundarbans landscape.[41]

The population size for the Bangladesh Sundarbans was estimated as 100–150 adult females or 335–500 tigers overall. Female home ranges, recorded using Global Positioning System collars, were some of the smallest recorded for tigers, indicating that the Bangladesh Sundarbans could have one of the highest densities and largest populations of tigers anywhere in the world. They are isolated from the next tiger population by a distance of up to 300 km (190 mi). Information is lacking on many aspects of Sundarbans tiger ecology, including relative abundance, population status, spatial dynamics, habitat selection, life history characteristics, taxonomy, genetics, and disease. There is also no monitoring program in place to track changes in the tiger population over time, and therefore no way of measuring the response of the population to conservation activities or threats. Most studies have focused on the tiger-human conflict in the area, but two studies in the Sundarbans East Wildlife sanctuary documented habitat-use patterns of tigers, and abundances of tiger prey, and another study investigated tiger parasite load. Some major threats to tigers have been identified. The tigers living in the Sundarbans are threatened by habitat destruction, prey depletion, highly aggressive and rampant intraspecific competition, tiger-human conflict, and direct tiger loss.[28]

Nepal

The tiger population in the Terai of Nepal is split into three isolated subpopulations that are separated by cultivation and densely settled habitat. The largest population lives in Chitwan National Park and in the adjacent Parsa Wildlife Reserve encompassing an area of 2,543 km2 (982 sq mi) of prime lowland forest. To the west, the Chitwan population is isolated from the one in Bardia National Park and adjacent unprotected habitat farther west, extending to within 15 km (9.3 mi) of the Shuklaphanta Wildlife Reserve, which harbours the smallest population.[42] The bottleneck between the Chitwan-Parsa and Bardia-Sukla Phanta metapopulations is situated just north of the town of Butwal.

As of 2009, an estimated 121 breeding tigers lived in Nepal.[43] By 2010, the number of adult tigers had reached 155.[44] A survey conducted from December 2009 to March 2010 indicates that 125 adult tigers live in Chitwan National Park and its border areas covering 1,261 km2 (487 sq mi).[45] From February to June 2013, a camera trapping survey was carried out in the Terai Arc Landscape, covering an area of 4,841 km2 (1,869 sq mi) in 14 districts. The country’s tiger population was estimated at 163–235 breeding adults comprising 102–152 tigers in the Chitwan-Parsa protected areas, 48–62 in the Bardia-Banke National Parks and 13–21 in the Shuklaphanta Wildlife Reserve.[46]

Bhutan

As of 2005, the population in Bhutan is estimated at 67–81 individuals.[8] Tigers occur from an altitude of 200 m (660 ft) in the subtropical Himalayan foothills in the south along the border with India to over 3,000 m (9,800 ft) in the temperate forests in the north, and are known from 17 of 18 districts. Their stronghold appears to be the central belt of the country ranging in altitude between 2,000 and 3,500 m (6,600 and 11,500 ft), between the Mo River in the west and the Kulong River in the east.[47] In 2010, camera traps recorded a pair of tigers at altitudes of 3,000 to 4,100 m (9,800 to 13,500 ft). The male was recorded scent-marking, and the female can also be seen to be lactating, confirming that the pair are living within their own territory, and strongly suggesting they are breeding at that altitude.[48]

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