Siberian tigers

The Siberian tiger or Amur tiger is a population of the tiger subspecies ''Panthera tigris tigris'' native to the Russian Far East, Northeast China and possibly North Korea. It once ranged throughout the Korean Peninsula, but currently inhabits mainly the Sikhote-Alin mountain region in southwest Primorye Province in the Russian Far East. In 2005, there were 331–393 adult and subadult Siberian tigers in this region, with a breeding adult population of about 250 individuals. The population had been stable for more than a decade because of intensive conservation efforts, but partial surveys conducted after 2005 indicate that the Russian tiger population was declining. An initial census held in 2015 indicated that the Siberian tiger population had increased to 480–540 individuals in the Russian Far East, including 100 cubs. This was followed up by a more detailed census which revealed there was a total population of 562 wild Siberian tigers in Russia. As of 2014, about 35 individuals were estimated to range in the international border area between Russia and China.

The Siberian tiger is genetically close to the now-extinct Caspian tiger. Results of a phylogeographic study comparing mitochondrial DNA from Caspian tigers and living tiger populations indicate that the common ancestor of the Siberian and Caspian tigers colonized Central Asia from eastern China, via the Gansu− Silk Road corridor, and then subsequently traversed Siberia eastward to establish the Siberian tiger population in the Russian Far East. The Caspian and Siberian tiger populations were the northernmost in mainland Asia.

The Siberian tiger was also called "Amur tiger", "Manchurian tiger", "Korean tiger", and " Ussurian tiger", depending on the region where individuals were observed.

Taxonomy

''Felis tigris'' was the scientific name proposed by Carl Linnaeus in 1758 for the tiger. In the 19th century, several tiger specimens were collected in East Asia and described:
*''Felis tigris altaicus'' proposed by Coenraad Jacob Temminck in 1844 were tiger skins with long hairs and dense coats sold in Japan, which originated in Korea, most likely from animals killed in the Altai and Pisihan Mountains.
*''Tigris longipilis'' proposed by Leopold Fitzinger in 1868 was based on a long-haired tiger skin in the Natural History Museum, Vienna.
*''Felis tigris'' var. ''amurensis'' proposed by Charles Dode in 1871 was based on tiger skins from the Amur region.
*''Felis tigris coreensis'' by Emil Brass in 1904 was a tiger skin from Korea.

The validity of several tiger subspecies was questioned in 1999. Most putative subspecies described in the 19th and 20th centuries were distinguished on the basis of fur length and colouration, striping patterns and body size – characteristics that vary widely within populations. Morphologically, tigers from different regions vary little, and gene flow between populations in those regions is considered to have been possible during the Pleistocene. Therefore, it was proposed to recognize only two tiger subspecies as valid, namely ''Panthera tigris tigris'' in mainland Asia, and '' P. t. sondaica'' in the Greater Sunda Islands and possibly in Sundaland.
In 2015, morphological, ecological and molecular traits of all putative tiger subspecies were analysed in a combined approach. Results support distinction of the two evolutionary groups: continental and Sunda tigers. The authors proposed recognition of only two subspecies: namely ''P. t. tigris'' comprising the Bengal, Malayan, Indochinese, South China, Siberian and Caspian tiger populations; and ''P. t. sondaica'' comprising the Javan, Bali and Sumatran tiger populations.

In 2017, the Cat Specialist Group revised felid taxonomy and now recognizes all the tiger populations in mainland Asia as ''P. t. tigris''.

Phylogeny

Several reports have been published since the 1990s on the genetic makeup of the Siberian tiger and its relationship to other populations. One of the most important outcomes has been the discovery of low genetic variability in the wild population, especially when it comes to maternal or mitochondrial DNA lineages. It seems that a single mtDNA haplotype almost completely dominates the maternal lineages of wild Siberian tigers. On the other hand, captive tigers appear to show higher mtDNA diversity. This may suggest that the subspecies has experienced a very recent genetic bottleneck caused by human pressure, with the founders of the captive population having been captured when genetic variability was higher in the wild.

At the start of the 21st century, researchers from the University of Oxford, U.S. National Cancer Institute and Hebrew University of Jerusalem collected tissue samples from 20 of 23 Caspian tiger specimens kept in museums across Eurasia. They sequenced at least one segment of five mitochondrial genes and found a low amount of variability of the mitochondrial DNA in Caspian tigers as compared to other tiger subspecies. They re-assessed the phylogenetic relationships of tiger subspecies and observed a remarkable similarity between Caspian and Siberian tigers, indicating that the Siberian tiger is the genetically closest living relative of the Caspian tiger, which strongly implies a very recent common ancestry. Based on phylogeographic analysis, they suggested that the ancestor of Caspian and Siberian tigers colonized Central Asia less than 10,000 years ago via the Gansu−Silk Road region from eastern China, and subsequently traversed eastward to establish the Siberian tiger population in the Russian Far East. The events of the Industrial Revolution may have been the critical factor in the reciprocal isolation of Caspian and Siberian tigers from what was likely a single contiguous population.

Samples of 95 wild Amur tigers were collected throughout their native range to investigate questions relative to population genetic structure and demographic history. Additionally, targeted individuals from the North American ''ex situ'' population were sampled to assess the genetic representation found in captivity. Population genetic and Bayesian structure analyses clearly identified two populations separated by a development corridor in Russia. Despite their well-documented 20th century decline, the researchers failed to find evidence of a recent population bottleneck, although genetic signatures of a historical contraction were detected. This disparity in signal may be due to several reasons, including historical paucity in population genetic variation associated with postglacial colonisation and potential gene flow from an extirpated Chinese population. The extent and distribution of genetic variation in captive and wild populations were similar, yet gene variants persisted ''ex situ'' that were lost ''in situ''. Overall, their results indicate the need to secure ecological connectivity between the two Russian populations to minimize loss of genetic diversity and overall susceptibility to stochastic events, and support a previous study suggesting that the captive population may be a reservoir of gene variants lost ''in situ''.

In 2013, the whole genome of the Siberian tiger was sequenced and published. Tigers in mainland Asia fall into two clades: the northern clade comprises the Siberian and Caspian tiger populations, and the southern clade all remaining continental tiger populations. A study published in 2018 was based on 32 tiger specimens using a whole-genome sequencing for analysis. Results support six monophyletic tiger clades and indicate that the most recent common ancestor lived about 110,000 years ago.

Characteristics

The tiger is reddish-rusty, or rusty-yellow in colour, with narrow black transverse stripes. The body length is not less than , condylobasal length of skull , zygomatic width , and length of upper carnassial tooth over long. It has an extended supple body standing on rather short legs with a fairly long tail.

Body size

In the 1980s, the typical weight range of wild Siberian tigers was indicated as for males and for females. Exceptionally large individuals were targeted and shot by hunters.

In 2005, a group of Russian, American and Indian zoologists published an analysis of historical and contemporary data on body weights of wild and captive tigers, both female and male across all subspecies. The data used include weights of tigers that were older than 35 months and measured in the presence of authors. Their comparison with historical data indicates that up to the first half of the 20th century both male and female Siberian tigers were on average heavier than post-1970 ones. The average historical wild male Siberian tiger weighed and the female ; the contemporary wild male Siberian tiger weighs on average with an asymptotic limit being ; a wild female weighs on average. Historical Siberian tigers and Bengal tigers were the largest ones, whereas contemporary Siberian tigers are on average lighter than Bengal tigers. The reduction of the body weight of today's Siberian tigers may be explained by concurrent causes, namely the reduced abundance of prey because of illegal hunting and that the individuals were usually sick or injured and captured in a conflict situation with people.

Measurements taken by scientists of the ''Siberian Tiger Project'' in the Sikhote-Alin range from in head and body length measured in straight line, with an average of for males; and for females ranging from with an average of . The average tail measures in males and in females. The longest male measured in total length including a tail of and with a chest girth of . The longest female measured in total length including tail of and with a chest girth of .
A male captured by members of the ''Siberian Tiger Project'' weighed , and the largest radio-collared male weighed .

The Siberian tiger is often considered to be the largest tiger.
A wild male, killed in Manchuria by the Sungari River in 1943, reportedly measured "over the curves", with a tail length of about . It weighed about . Dubious sources mention weights of and even .

Skull

The skull of the Siberian tiger is characterized by its large size. The facial region is very powerful and very broad in the region of the canines. The skull prominences, especially in the sagittal crest and crista occipitalis, are very high and strong in old males, and often much more massive than usually observed in the biggest skulls of Bengal tigers. The size variation in skulls of Siberian tigers ranges from in nine individuals measured. A female skull is always smaller and never as heavily built and robust as that of a male. The height of the sagittal crest in its middle part reaches as much as , and in its posterior part up to .

Female skulls range from . The skulls of male Caspian tigers from Turkestan had a maximum length of , while that of females measured . A tiger killed on the Sumbar River in Kopet Dag in January 1954 had a greatest skull length of , which is considerably more than the known maximum for this population and slightly exceeds that of most Siberian tigers. However, its condylobasal length was only , smaller than those of the Siberian tigers, with a maximum recorded condylobasal length of . The biggest skull of a Siberian tiger from northeast China measured in length, which is about more than the maximum skull lengths of tigers from the Amur region and northern India, with the exception of a skull of a northern Indian tiger from the vicinity of Nagina, which measured "over the bone".

Fur and coat

The ground colour of Siberian tigers' pelage is often very pale, especially in winter coat. However, variations within populations may be considerable. Individual variation is also found in form, length, and partly in colour, of the dark stripes, which have been described as being dark brown rather than black.

The fur of the Siberian tiger is moderately thick, coarse and sparse compared to that of other felids living in the former Soviet Union. Compared to the extinct westernmost populations, the Siberian tiger's summer and winter coats contrast sharply with other subspecies. Generally, the coat of western populations was brighter and more uniform than that of the Far Eastern populations. The summer coat is coarse, while the winter coat is denser, longer, softer, and silkier. The winter fur often appears quite shaggy on the trunk and is markedly longer on the head, almost covering the ears. Siberian and Caspian tigers had the thickest fur amongst tigers.

The whiskers and hair on the back of the head and the top of the neck are also greatly elongated. The background colour of the winter coat is generally less bright and rusty compared to that of the summer coat. Because of the winter fur's greater length, the stripes appear broader with less defined outlines. The summer fur on the back is long, along the top of the neck, on the abdomen, and on the tail. The winter fur on the back is , on the top of the neck, on the throat, on the chest and on the abdomen. The whiskers are .

Distribution and habitat

The Siberian tiger once inhabited much of the Korean Peninsula, Manchuria and other parts of north-eastern China, the eastern part of Siberia and the Russian Far East, perhaps as far west as Mongolia and the area of Lake Baikal, where the Caspian tiger also reportedly occurred.
During the late Pleistocene and Holocene, it was likely connected to the South China tiger population through corridors in the Yellow River basin, before humans interrupted gene flow.

Today, its range stretches south to north for almost the length of Primorsky Krai and into southern Khabarovsk Krai east and south of the Amur River. It also occurs within the Greater Xing'an Range, which crosses into Russia from China at several places in southwest Primorye. This region represents a merger zone of the East Asian temperate broadleaf and mixed forest and the taiga, resulting in a mosaic of forest types that vary in elevation and topography. Key habitats of the Siberian tiger are Korean pine forests with a complex composition and structure.

The faunal complex of the region is represented by a mixture of Asian and boreal life forms. The ungulate complex is represented by seven species, with Manchurian wapiti, Siberian roe deer, and wild boar being the most common throughout the Sikhote-Alin mountains but rare in higher altitude spruce-fir forests. Sika deer are restricted to the southern half of the Sikhote-Alin mountains. Siberian musk deer and Amur moose are associated with the conifer forests and are near the southern limits of their distribution in the central Sikhote-Alin mountains.

In 2005, the number of Amur tigers in China was estimated at 18–22, and 331–393 in the Russian Far East, comprising a breeding adult population of about 250, fewer than 100 likely to be sub-adults, more than 20 likely to be less than 3 years of age. More than 90% of the population occurred in the Sikhote Alin mountain region. An unknown number of tigers survive in the reserve areas around Baekdu Mountain, on the border between China and North Korea, based on tracks and sightings.

In August 2012, a Siberian tiger with four cubs was recorded for the first time in northeastern China's Hunchun National Nature Reserve located in the vicinity of the international borders with Russia and North Korea. Camera-trap surveys carried out in the spring seasons of 2013 and 2014 revealed between 27 and 34 tigers along the China-Russian border.
In April 2014, World Wide Fund for Nature personnel captured a video of a tigress with cubs in inland China.
The tiger population in the Changbai Mountains dispersed westwards between 2003 and 2016.
Camera trap surveys between 2013 and 2018 revealed about 55 Siberian tigers in four forested landscapes in northeastern China: Laoyeling, Zhangguangcai Range, Wandashan and Lesser Khingan Mountains. Feces, urine and hair was used to genetically identify 30 tigers in this region. However, only Laoyeling is thought to support a breeding population.

Ecology and behavior

Siberian tigers are known to travel up to over ecologically unbroken country. In 1992 and 1993, the maximum total population density of the Sikhote-Alin tiger population was estimated at 0.62 tigers in . The maximum ''adult'' population estimated in 1993 reached 0.3 tigers in , with a sex ratio of averaging 2.4 females per male. These density values were much lower than what had been reported for other subspecies at the time.
In 2004, dramatic changes in land tenure, population density, and reproductive output in the core area of the Sikhote-Alin Zapovednik Siberian Tiger Project were detected, suggesting that when tigers are well protected from human-induced mortality for long periods, the adult female population density increases significantly. When more adult females survived, the mothers shared their home ranges with their daughters once the daughters reached maturity. By 2007, population density of tigers was estimated at 0.8±0.4 tigers in in the southern part of Sikhote-Alin Zapovednik, and 0.6±0.3 tigers in in the central part of the protected area.

Siberian tigers share habitat with Amur leopards (''P. pardus orientalis''), but in the Changbai Mountains have been recorded more often in lower elevations than leopards.

Hunting and diet

Prey species of the tiger include ungulates such as Manchurian wapiti (''Cervus canadensis xanthopygus''), Siberian musk deer (''Moschus moschiferus''), long-tailed goral (''Naemorhedus caudatus''), moose (''Alces alces''), Siberian roe deer (''Capreolus pygargus'') and sika deer (''Cervus nippon''), wild boar (''Sus scrofa''), and even sometimes small size Asiatic black bears (''Ursus thibetanus'') and brown bears (''Ursus arctos''). Siberian tigers also take smaller prey like hares, rabbits, pikas and even salmon. Scat was collected along the international border between Russia and China between November 2014 and April 2015; 115 scat samples of nine tigers contained foremost remains of wild boar, sika deer and roe deer.

Between January 1992 and November 1994, 11 tigers were captured, fitted with radio-collars and monitored for more than 15 months in the eastern slopes of the Sikhote-Alin mountain range. Results of this study indicate that their distribution is closely associated with distribution of Manchurian wapiti, while distribution of wild boar was not such a strong predictor for tiger distribution. Although they prey on both Siberian roe deer and sika deer, overlap of these ungulates with tigers was low. Distribution of moose was poorly associated with tiger distribution. The distribution of preferred habitat of key prey species was an accurate predictor of tiger distribution.

Results of a three-year study on Siberian tigers indicate that the mean interval between their kills and estimated prey consumption varied across seasons: during 2009 to 2012, three adult tigers killed prey every 7.4 days in summer and consumed a daily average of ; in winter they killed more large-bodied prey, made kills every 5.7 days and consumed a daily average of .

Interspecific predatory relationships

Following a decrease of ungulate populations from 1944 to 1959, more than 32 cases of Amur tigers attacking both Ussuri brown (''Ursus arctos lasiotus'') and Ussuri black bears (''U. thibetanus ussuricus'') were recorded in the Russian Far East, and hair of bears were found in several tiger scat samples. Tigers attack black bears less often than brown bears, as the latter live in more open habitats and are not able to climb trees. In the same time period, four cases of brown bears killing female tigers and young cubs were reported, both in disputes over prey and in self-defense. Tigers can tackle bears larger than themselves, using an ambushing tactic and jumping onto the bear from an overhead position, grabbing it by the chin with one forepaw and by the throat with the other, and then killing it with a bite in the spinal column. Tigers mainly feed on the bear's fat deposits, such as the back, hams and groin.

When Amur tigers prey on brown bears, they usually target young and sub-adult bears, besides small female adults. Predation by tigers on denned brown bears was not detected during a study carried between 1993 and 2002. Ussuri brown bears, along with the smaller black bears constitute 2.1% of the Siberian tiger's annual diet, of which 1.4% are brown bears.

The effect the presence of tigers has on brown bear behavior seems to vary. In the winters of 1970–1973, Yudakov and Nikolaev recorded two cases of bears showing no fear of tigers and another case of a brown bear changing path upon crossing tiger tracks. Other researchers have observed bears following tiger tracks to scavenge tiger kills and to potentially prey on tigers. Despite the threat of predation, some brown bears actually benefit from the presence of tigers by appropriating tiger kills that the bears may not be able to successfully hunt themselves. Brown bears generally prefer to contest the much smaller female tigers. During telemetry research in the Sikhote-Alin Nature Reserve, 44 direct confrontations between bears and tigers were observed, in which bears in general were killed in 22 cases, and tigers in 12 cases. There are reports of brown bears specifically targeting Amur leopards and tigers to abstract their prey. In the Sikhote-Alin reserve, 35% of tiger kills were stolen by bears, with tigers either departing entirely or leaving part of the kill for the bear. Some studies show that bears frequently track down tigers to usurp their kills, with occasional fatal outcomes for the tiger. A report from 1973 describes twelve known cases of brown bears killing tigers, including adult males; in all cases the tigers were subsequently eaten by the bears.

The relationship between the Amur tiger and the Himalayan bear is not specifically studied. Numerous publications on these species there are mainly episodic and survey data on this issue are collected by different authors in selected areas which do not give a complete picture of the nature.

Tigers depress wolf (''Canis lupus'') numbers, either to the point of localized extinction or to such low numbers as to make them a functionally insignificant component of the ecosystem. Wolves appear capable of escaping competitive exclusion from tigers only when human pressure decreases tiger numbers. In areas where wolves and tigers share ranges, the two species typically display a great deal of dietary overlap, resulting in intense competition. Wolf and tiger interactions are well documented in Sikhote-Alin, where until the beginning of the 20th century, very few wolves were sighted. Wolf numbers may have increased in the region after tigers were largely eliminated during the Russian colonisation in the late 19th century and early 20th century. This is corroborated by native inhabitants of the region claiming that they had no memory of wolves inhabiting Sikhote-Alin until the 1930s, when tiger numbers decreased. Today, wolves are considered scarce in tiger habitat, being found in scattered pockets, and usually seen travelling as loners or in small groups. First hand accounts on interactions between the two species indicate that tigers occasionally chase wolves from their kills, while wolves will scavenge from tiger kills. Tigers are not known to prey on wolves, though there are four records of tigers killing wolves without consuming them. Tigers recently released are also said to hunt wolves.

This competitive exclusion of wolves by tigers has been used by Russian conservationists to convince hunters in the Far East to tolerate the big cats, as they limit ungulate populations less than wolves, and are effective in controlling wolf numbers.

Siberian tigers also compete with the Eurasian lynx (''Lynx lynx'') and occasionally kill and eat them. Eurasian lynx remains have been found in the stomach contents of Siberian tigers in Russia. In March 2014, a dead lynx discovered in Bastak Nature Reserve bore evidence of predation by a Siberian tiger. The tiger apparently ambushed, pursued, and killed the lynx but only consumed it partially. This incident marks one of the first documented cases of a tiger preying on a lynx, and indicates that the tiger might have been more intent on eliminating a competitor than on catching prey.

Reproduction and life cycle

Siberian tigers mate at any time of the year. A female signals her receptiveness by leaving urine deposits and scratch marks on trees. She will spend 5 or 6 days with the male, during which she is receptive for three days. Gestation lasts from 3 to 3½ months. Litter size is normally two or four cubs but there can be as many as six. The cubs are born blind in a sheltered den and are left alone when the female leaves to hunt for food. Cubs are divided equally between sexes at birth. However, by adulthood there are usually two to four females for every male. The female cubs remain with their mothers longer, and later they establish territories close to their original ranges. Males, on the other hand, travel unaccompanied and range farther earlier in their lives, making them more vulnerable to poachers and other tigers.
A Siberian tiger family comprising an adult male, a female and three cubs were recorded in 2015.

At 35 months of age, tigers are sub-adults. Males reach sexual maturity at the age of 48 to 60 months.

The average lifespan for Siberian tigers ranges from 16–18 years. Wild individuals tend to live between 10–15 years, while in captivity individuals may live up to 25 years.

Threats

Results of genetic analysis of 95 wild Siberian tiger samples from Russia revealed that genetic diversity is low, only 27–35 individuals contributed to their genes. Further exacerbating the problem is that more than 90% of the population occurred in the Sikhote Alin mountain region. Tigers rarely move across the development corridor, which separates this sub-population from the much smaller sub-population in southwest Primorye province.

The winter of 2006–2007 was marked by heavy poaching. Poaching of tigers and their wild prey species is considered to be driving the decline, although heavy snows in the winter of 2009 could have biased the data. In northern China’s Huang Ni He National Nature Reserve, poachers set up foremost snare traps, but there is not sufficient personnel to patrol this area throughout the year. In Hunchun National Nature Reserve, poaching of ungulate species impedes recovery of the tiger population.

In the past

After the dissolution of the Soviet Union, illegal deforestation and bribery of park rangers facilitated poaching of Siberian tigers. Local hunters had access to a formerly sealed off lucrative Chinese market, and this once again put the region's tiger population at risk of extinction. While improvement in the local economy has led to greater resources being invested in conservation efforts, an increase in economic activity has led to an increased rate of development and deforestation. The major obstacle in preserving the tiger is the enormous territory individual tigers require; up to is needed by a single female and more for a single male.

The Siberian tiger was once common in the Korean Peninsula. It was eradicated during the period of Korea under Japanese rule between 1910 and 1945.

Conservation

Tigers are included on CITES Appendix I, banning international trade. All tiger range states and countries with consumer markets have banned domestic trade as well. At the 14th Conference of the Parties to CITES in 2007, stronger enforcement measures were called for, as well as an end to tiger farming.

In 1992, the ''Siberian Tiger Project'' was founded, with the aim of providing a comprehensive picture of the ecology of the Amur tiger and the role of tigers in the Russian Far East through scientific studies. By capturing and outfitting tigers with radio collars, their social structure, land use patterns, food habits, reproduction, mortality patterns and their relation with other inhabitants of the ecosystem, including humans is studied. These data compilations will hopefully contribute toward minimizing poaching threats because of traditional hunting. The ''Siberian Tiger Project'' has been productive in increasing local capacity to address human-tiger conflict with a ''Tiger Response Team'', part of the Russian government's ''Inspection Tiger'', which responds to all tiger-human conflicts; by continuing to enhance the large database on tiger ecology and conservation with the goal of creating a comprehensive Siberian tiger conservation plan; and training the next generation of Russian conservation biologists.

In August 2010, China and Russia agreed to enhance conservation and cooperation in protected areas in a transboundary area for Amur tigers. China has undertaken a series of public awareness campaigns including celebration of the first ''Global Tiger Day'' in July 2010, and ''International Forum on Tiger Conservation and Tiger Culture'' and ''China 2010 Hunchun Amur Tiger Culture Festival'' in August 2010.Global Tiger Initiative. (2011)
''Global Tiger Recovery Program 2010–2022''
. Global Tiger Initiative Secretariat, Washington.

Reintroduction

Inspired by findings that the Amur tiger is the closest relative of the Caspian tiger, there has been discussion whether the Amur tiger could be an appropriate subspecies for reintroduction into a safe place in Central Asia. The Amu-Darya Delta was suggested as a potential site for such a project. A feasibility study was initiated to investigate if the area is suitable and if such an initiative would receive support from relevant decision makers. A viable tiger population of about 100 animals would require at least of large tracts of contiguous habitat with rich prey populations. Such habitat is not presently available in the delta and so cannot be provided in the short term. The proposed region is therefore unsuitable for the reintroduction, at least at this stage of development.

A second possible introduction site in Kazakhstan is the Ili River delta at the southern edge of Lake Balkhash. The delta is situated between the Saryesik-Atyrau Desert

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