THE BLUE - FOOTED BOOBY

The blue-footed booby (Sula nebouxii) is a marine bird native to subtropical and tropical regions of the eastern Pacific Ocean. It is one of six species of the genus Sula – known as boobies. It is easily recognizable by its distinctive bright blue feet, which is a sexually selected trait. Males display their feet in an elaborate mating ritual by lifting them up and down while strutting before the female. The female is slightly larger than the male and can measure up to 90 cm (35 in) long with a wingspan of up to 1.5 m (5 ft).^[2]
The natural breeding habitats of the blue-footed booby are the tropical and subtropical islands of the Pacific Ocean. It can be found from the Gulf of California down along the western coasts of Central and South America down to Peru. Approximately one half of all breeding pairs nest on the Galápagos Islands.^[3] Its diet mainly consists of fish, which it obtains by diving and sometimes swimming underwater in search of its prey. It sometimes hunts alone, but usually hunts in groups.^[4]

A blue footed booby on the Galapagos Islands.

The blue-footed booby usually lays one to three eggs at a time. The species practices asynchronous hatching, in contrast to many other species whereby incubation begins when the last egg is laid and all chicks hatch together. This results in a growth inequality and size disparity between siblings, leading to facultative siblicide in times of food scarcity.^[5] This makes the blue-footed booby an important model for studying parent-offspring conflict and sibling rivalry.

 

 

Taxonomy

The blue-footed booby was described by the French naturalist Alphonse Milne-Edwards in 1882 under the current binomial name Sula nebouxii.^[6] The specific epithet was chosen to honor the surgeon, naturalist, and explorer Adolphe-Simon Neboux (1806-1844).^[7] There are two recognized subspecies:^[8]

• Sula nebouxii nebouxii Milne-Edwards, 1882 – Pacific coast of Southern and Middle America
• Sula nebouxii excisa Todd, 1948 – Galapagos Islands^[9]

Its closest relative is the Peruvian booby. It is likely that the two species split from each other recently due to their shared ecological and biological characteristics.^[10] A 2011 study of multiple genes calculated the two species diverged between 1.1 and 0.8 million years ago.^[11]
The name booby comes from the Spanish word bobo ("stupid", "foolish", or "clown") because the blue-footed booby is, like other seabirds, clumsy on land.^[3] They are also regarded as foolish for their apparent fearlessness of humans.^[2]

Description

Clearly showing the white underparts unlike the dark brown wings and the blue-legged legs.

Neck and head of a blue-footed booby showing distinctive coloring and beak

The male (left) has a smaller pupil and slightly lighter feet and is smaller in size than the female.

The blue-footed booby is on average 81 cm (32 in) long and weighs 1.5 kg (3.3 lb), with the female being slightly larger than the male. Its wings are long and pointed and brown in color. The neck and head of the blue-footed booby are light brown with white streaks while the belly and underside exhibit pure white plumage.^[12] Its eyes are placed on either side of its bill and oriented towards the front, enabling excellent binocular vision. Its eyes are a distinctive yellow, with the male having more yellow in its irises than the female. Blue-footed booby chicks have black beaks and feet and are clad in a layer of soft white down. The subspecies S. n. excisa that breeds on the Galapagos Islands is larger than the nominate subspecies and has lighter plumage especially around the neck and head.^[9]
The Peruvian booby is similar in appearance but has grey feet, whiter head and neck, and white spots on its wing coverts. The ranges of the two species overlap in the waters of northern Peru and southern Ecuador.^[13]
Since the blue-footed booby preys on fish by diving headlong into the water, its nostrils are permanently closed, and it has to breathe through the corners of its mouth. Its most notable characteristic is its blue-colored feet, which can range in color from a pale turquoise to a deep aquamarine. Males and younger birds have lighter feet than females.^[2] Its blue feet play a key role in courtship rituals and breeding, with the male visually displaying its feet to attract mates during the breeding season.

Distribution and habitat

The blue-footed booby is distributed among the continental coasts of the eastern Pacific Ocean from California to the Galápagos Islands down into Peru.^[14] It is strictly a marine bird. Its only need for land is to breed and rear young, which it does along the rocky coasts of the eastern Pacific.^[13]
A booby may use and defend two or three nesting sites, which consist of bare black lava in small divots in the ground, until they develop a preference for one a few weeks before the eggs are laid. These nests are created as parts of large colonies. While nesting, the female will turn to face the sun throughout the day, so the nest is surrounded by excrement.

Natal dispersal

Females start breeding when they are 1 to 6 years old, while males start breeding when they are 2 to 6 years old. There is very limited natal dispersal, meaning that young pairs do not move far from their original natal nests for their own first reproduction, leading to the congregation of hundreds of boobies in dense colonies. The benefit of limited dispersal is that by staying close to their parents' nesting sites, the boobies are more likely to have a high-quality nest. Since their parents had successfully raised chicks to reproductive age, their nest site must have been effective, either by providing cover from predation and parasitism, or by its suitability for taking off and landing.^[15] Bigamy has been observed in the species, and there are known cases where two females and one male all share a single nest.^[16]

Foot pigmentation

Detail of leg and feet

The blue color of the blue-footed booby's webbed feet comes from carotenoid pigments obtained from its diet of fresh fish. Carotenoids act as antioxidants and stimulants for the blue-footed booby's immune function, suggesting that carotenoid-pigmentation is an indicator of an individual's immunological state.^[17] Blue feet also indicate the current health condition of a booby. Boobies that were experimentally food-deprived for forty-eight hours experienced a decrease in foot brightness due to a reduction in the amount of lipids and lipoproteins that are used to absorb and transport carotenoids. Thus, the feet are rapid and honest indicators of a booby's current level of nourishment.^[17] As blue feet are signals that reliably indicate the immunological and health condition of a booby, coloration is favored through sexual selection.

Female selection

The brightness of the feet decreases with age, so females tend to mate with younger males with brighter feet, who have higher fertility and greater ability to provide paternal care than older males. In a cross-fostering experiment, it was observed that foot color reflects paternal contribution to raising chicks; chicks raised by foster fathers with brighter feet grew faster than chicks raised by foster males with duller feet.^[18] Females continuously evaluate their partners' condition based on foot color. In one experiment, males whose partners had laid a first egg in the nest had their feet dulled by make-up. The female partners laid smaller second eggs a few days later. As duller feet usually indicate a decrease in health and possibly genetic quality, it is adaptive for these females to decrease their investment in the second egg. The smaller second eggs contained less yolk concentration, which could influence embryo development, hatching success, and subsequent chick growth and survival. In addition, they contained less yolk androgens.^[19] As androgen plays an important role in chick survival, the experiment suggested female blue-footed boobies use the attractiveness and perceived genetic quality of their mates to determine how much resources they should allocate to their eggs.^[17] This supports the differential allocation theory, which predicts that parents invest more in the care of their offspring when paired with attractive mates.^[17]

Male selection

Males also assess their partner's reproductive value and adjust their own investment in the brood according to their partner's condition. Females that lay larger and brighter eggs are in better condition and have greater reproductive value. Therefore, males tend to display higher attentiveness and parental care to larger eggs, since those eggs were produced by a female with apparent good genetic quality. Smaller, duller eggs garnered less paternal care. Female foot color is also observed as an indication of perceived female condition. In one experiment, the color of eggs was muted by researchers, it was found that males were willing to exercise similar care for both large eggs and small eggs if his mate had brightly colored feet, whereas males paired with dull-footed females only incubated larger eggs. Interestingly, researchers also found that males did not increase their care when females exhibited both bright feet and high-quality offspring.^[20]

Behavior and ecology

Hunting and feeding

Sequence showing plunge-diving from beginning to end

Blue-footed boobies fishing in a large group

The blue-footed booby is a specialized fish eater, feeding on small schooling fish such as sardines, anchovies, mackerel, and flying fish. It will also take squid and offal. The blue-footed booby hunts by diving into the ocean after prey, sometimes from a great height, and can also swim underwater in pursuit of its prey. It can hunt singly, in pairs, or in larger flocks. Boobies travel in parties of about 12 to areas of water with large schools of small fish. When the lead bird sees a fish shoal in the water, it will signal to the rest of the group and they will all dive in unison, pointing their bodies down like arrows.^[4]
Plunge diving can be done from heights of 10–30.5 m (33–100 ft) and even up to 100 m (330 ft). These birds hit the water around 97 km/h (60 mph) and can go to depths of 25 m (82 ft) below the water surface. Their skulls contain special air sacs that protect the brain from enormous pressure.^[2] Prey are usually eaten while the birds are still underwater. Surprisingly, individuals prefer to eat on their own instead of with their hunting group, usually in the early morning or late afternoon.^[21] Males and females fish differently, which may contribute to why blue-foots, unlike other boobies, raise more than one young. The male is smaller and has a proportionally larger tail, which enables the male to fish in shallow areas as well as deep waters. The female is larger and can carry more food. Both the male and female feed the chicks through regurgitation.^[21]

Breeding

Displaying (sky-pointing)

Another way of displaying by raising a foot

The blue-footed booby is monogamous, although it has the potential to be bigamous.^[16] It is an opportunistic breeder, with the breeding cycle occurring every 8 to 9 months.^[22] The courtship of the blue-footed booby consists of the male flaunting his blue feet and dancing to impress the female. The male begins by showing his feet, strutting in front of the female. Then, he presents nest materials and finishes the mating ritual with a final display of his feet.^[23] The dance also includes "sky-pointing", which involves the male pointing his head and bill up to the sky while keeping the wings and tail raised.^[24]

Rearing young

With egg and new young

The blue-footed booby is one of only two species of booby that raises more than one chick in a breeding cycle.
The female blue-footed booby lays two or three eggs. Eggs are laid about four to five days apart. Both male and female take turns incubating the eggs, while the non-sitting bird keeps watch. Since the blue-footed booby does not have a brooding patch, it uses its feet to keep the eggs warm. The incubation period is 41–45 days. Usually, one to two chicks are hatched from the two to three eggs originally laid. The male and female share parental responsibilities. The male will provide food for the young in the first part of their life because of his specialized diving. The female will take over when the demand is higher.^[10] Chicks feed off the regurgitated fish in the adult's mouth. If the parent blue-footed booby does not have enough food for all of the chicks, it will only feed the biggest chick, ensuring that at least one will survive.^[5]

Sula nebouxii chick

Like other sexually size-dimorphic birds, female blue-footed boobies usually favor the smaller sex during times of food scarcity. Booby chicks do not show clear differences in size based on sex, but females do grow faster than males, which means they require greater parental investment. Blue-footed boobies display behavior that is described in the Flexible Investment Hypothesis, which states that a female will adjust the allocation of resources to maximize her lifetime reproductive success. This was shown in an experiment in which females had their flight feathers trimmed, so that they had to expend more energy during flights to obtain food for their broods. Female chicks of such mothers were more strongly affected than their brothers, in that they had lower masses and shorter wing lengths.^[25]

Brood hierarchy due to asynchronous hatching

The blue-footed booby lays one to three eggs in one nest at a time, although 80% of nests only contain two eggs.^[26] Eggs are laid five days apart. After the first egg is laid, it is immediately incubated, which results in a difference in chick hatching times. The first chick hatches four days before the other, so it receives a four-day head start in growth compared to its younger sibling. This asynchronous hatching serves many purposes. First, it spaces out the difficult time period in rearing during which newborn chicks are too feeble to accept regurgitated food. In addition, it reduces the chance that parents will suffer total brood loss to predators such as the milk snake.^[27]
Experiments have shown that asynchronous hatching may also reduce sibling rivalry. Experimentally manipulated synchronous broods produced more aggressive chicks; chicks in asynchronous broods were less violent. This pattern of behavior arguably occurs through a clearly established brood hierarchy in asynchronously hatched siblings. Although asynchronous hatching is not vital for the formation of brood hierarchies (the experimentally synchronous broods established them as well), it does aid in efficient brood reduction when food levels are low. Subordinate chicks in asynchronous broods die more quickly, thus relieving the parents of the burden of feeding both offspring when resources are insufficient to properly do so.^[28]

Facultative siblicide

Blue-footed booby chicks practice facultative siblicide, opting to cause the death of a sibling based on environmental conditions. The A-chick, who hatches first, will kill the younger B-chick if there is a food shortage. The initial size disparity between the A-chick and B-chick is retained for at least the first two months of life.^[27] During lean times, the A-chick may attack the B-chick by pecking at their younger sibling vigorously, or it may simply drag its younger sibling by the neck and oust it from the nest. Experiments in which the necks of chicks were taped to inhibit food ingestion showed that sibling aggression increased sharply when the weight of the A-chicks dropped below 20-25% of their potential. There was a steep increase in pecking below that threshold, indicating that siblicide is, in part, triggered by the dominant chick's weight, and not simply by the size difference between the siblings. It was also discovered that younger broods (those less than six weeks old) had three times the rate of pecking than older broods. This is perhaps due to the relative inability of young B-chicks to defend themselves against an A-chick attack.^[29]
The elder sibling also may harm the younger one by controlling access to the food delivered by the parents. A-chicks always receive food before B-chicks. Although subordinate chicks beg just as much as their dominant siblings, the older chicks are able to divert the parents' attention to themselves, as their large size and conspicuousness serve as more effective stimuli.^[27]
However, another experiment showed that booby chicks do not operate exclusively by the Leftovers Hypothesis, where younger chicks are fed only after the elder ones are completely satiated. Instead, researchers identified a certain degree of tolerance towards the younger sibling during short-term periods of food shortages. This Tolerance Hypothesis suggests that the elder chicks will reduce food intake moderately, just enough so that the younger sibling does not starve. Although this system works during short-term food shortages, it is unsustainable during prolonged periods of dearth. In this latter case, the elder sibling will usually become aggressive and siblicidal.^[30]

Parental role in siblicide

In flight

Blue-footed booby parents are passive spectators of this intrabrood conflict. They do not intervene in their offspring's struggles, even at the point of siblicide. Booby parents even appear to facilitate the demise of the younger sibling by creating and maintaining the inequality between the two chicks. They reinforce the brood hierarchy by feeding the dominant chick more often than the subordinate one. Thus, they respond to the brood hierarchy and not to the level of begging when deciding which chick to feed, as both chicks beg in equal amounts. This level of passivity towards the very possible death of their younger offspring may be an indication that brood reduction is advantageous for the parents.^[29] The Insurance Egg Hypothesis views the second egg and resulting chick as insurance for the parent in case the first egg does not hatch, or if food levels are higher than expected.^[26]
However, booby parents may not be as indifferent as they seem. Experimental evidence suggests that the parental behavior described above may be masking parent-offspring conflict. It was discovered that blue-footed booby parents make steep-sided nests that serve to deter the early ejection of the younger chick by the older sibling. This is in direct contrast to the masked booby, a species in which siblicide is obligate due to the ease in which older siblings can eject younger chicks from their flat nests. When blue-footed booby nests were experimentally flattened, parents restored them to their original steepness.^[31] In another experiment, blue-footed booby chicks that were placed in masked booby nests were more likely to engage in siblicide, which reveals that parental care somehow affects the level of siblicide.^[32] Parents also appear to respond more frequently to chicks that are in poorer body conditions during periods of food deprivation.^[33] Egg-mass analysis shows that in clutches produced at the beginning of the breeding season, the second egg in a nest were, on average, 1.5% heavier than the first. Since heavier eggs give rise to heavier chicks that have greater fitness, this evidence indicates that parents may try to rectify any disadvantages that accompany a late hatching date by investing more into the second egg.^[34] Hormonal analysis of eggs also shows that there appears to be no parental favoritism in regards to androgen allocation. It is important to note, however, that this may simply be that the species has evolved simpler ways to manipulate asymmetries and maximize parental reproductive output.^[35] Experiments show that what may at first appear to be parental cooperation with the elder chick may in fact mask a genetic parent-offspring conflict.^[36]

Long-term effects of hierarchies

There is always a dominant-subordinate relationship between chicks in a brood. Although dominant A-chicks grow faster and survive past infancy more often than the subordinate B-chick, there is actually no difference in reproductive success between the two types of siblings during adulthood. In one longitudinal study, there appears to be no long-term effects of dominance hierarchies; in fact, subordinate chicks were often observed producing nests of their own before their dominant siblings.^[36]

Communication

Blue-footed boobies make raucous or polysyllabic grunts or shouts and thin whistling noises. The males of the species have been known to throw up their head and whistle at a passing, flying female. Their ritual displays are also a form of communication.
Mates can recognize each other by their calls. Researchers have analyzed calls of blue-footed boobies and conducted playback experiments. Although calls differed between sexes, unique individual signatures were present. It was found that both males and females can discriminate the calls of their mates from others.^[37]

Population decline

Concerns of a decline in the booby population of the Galapagos Islands prompted a research project in its cause. The project, completed in April 2014, confirmed the population decline.^[38] The blue-footed booby population appears to be having trouble breeding and thus is slowly declining. The decline is feared to be long-term, but annual data collection is needed for a firm conclusion that this is not a normal fluctuation.
Food problems may be the cause of an observed failure of the birds to even try to breed. The results of the research suggest this is related to a decline in sardines (Sardinops sagax), an important part of the boobies’ diet. Earlier work on Española Island saw successful breeding in blue-footed boobies that have access to sardines, in which case their diet consists essentially wholly of sardines. However, sardines have been largely absent from the Española area since 1997, as has been shown from Nazca boobies there, who also prefer sardines but can breed using other prey. In 2012–13, roughly only half of prey items in the boobies' diet were sardines. No evidence was seen of other possible causes for the decline, such as effects of humans, introduced predators, or disease.^[39]

 

THE TIGERS

The tiger (Panthera tigris) is the largest cat species, most recognizable for its pattern of dark vertical stripes on reddish-orange fur with a lighter underside. The species is classified in the genus Panthera with the lion, leopard, jaguar, and snow leopard. It is an apex predator, primarily preying on ungulates such as deer and bovids. It is territorial and generally a solitary but social predator, often requiring large contiguous areas of habitat that support its prey requirements. This, coupled with the fact that it is indigenous to some of the more densely populated places on Earth, has caused significant conflicts with humans.
Tiger populations once ranged widely across Eurasia, from the Black Sea in the west, to the Indian Ocean in the south, and from Kolyma to Sumatra in the east. Over the past 100 years, they have lost 93% of their historic range, and have been extirpated from Western and Central Asia, from the islands of Java and Bali, and from large areas of Southeast, South, and East Asia. Today, they range from the Siberian taiga to open grasslands and tropical mangrove swamps. The species has been classified as endangered in the IUCN Red List. Major reasons for population decline include habitat destruction, habitat fragmentation and poaching. The extent of area inhabited by tigers is estimated at less than 1,184,911 km² (457,497 sq mi), a 41% decline from the area estimated in the mid-1990s. The global wild population is estimated to number between 3,062 and 3,948 individuals, down from around 100,000 at the start of the 20th century, with most remaining populations occurring in small pockets isolated from each other, in which about 2,000 tigers live on the Indian subcontinent.^[1] In 2016, an estimate of a global wild tiger population of approximately 3,890 individuals was presented during the Third Asia Ministerial Conference on Tiger Conservation.^[4][5] The WWF declared that the world's count of wild tigers has risen for the first time in a century.^[6]
The tiger is among the most recognisable and popular of the world's charismatic megafauna. It featured prominently in ancient mythology and folklore, and continues to be depicted in modern films and literature, appearing on many flags, coats of arms, and as mascots for sporting teams. The tiger is the national animal of Bangladesh, India, Malaysia and South Korea.

 

 

 Etymology

The word Panthera is probably of Oriental origin and retraceable to the Ancient Greek word panther, the Latin word panthera, the Old French word pantère, most likely meaning "the yellowish animal", or from pandarah meaning whitish-yellow. The derivation from Greek pan- ("all") and ther ("beast") may be folk etymology.^[7]
The word specific name tigris derives from the Classical Greek language τίγρις meaning "tiger" as well as the river Tigris.^[8]
The Middle English tigre and the Old English tigras (a plural word) were both used for the animal.^[9] These derive from the Old French tigre, itself a derivative of the Latin word tigris. The original source may have been the Persian tigra meaning pointed or sharp and the Avestan tigrhi meaning an arrow, perhaps referring to the speed with which a tiger launches itself at its prey.^[10]

Taxonomy

 


In 1758, Carl Linnaeus described the tiger in his work Systema Naturae and gave it the scientific name Felis tigris.^[3] In 1929, the British taxonomist Reginald Innes Pocock subordinated the species under the genus Panthera using the scientific name Panthera tigris.^[11][12]

Recent subspecies

Following Linnaeus's first descriptions of the species, several tiger specimens were described and proposed as subspecies.^[13] The validity of several tiger subspecies was questioned in 1999. Most putative subspecies described in the 19th and 20th centuries were distinguished on basis of fur length and coloration, striping patterns and body size, hence 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 P. t. tigris in mainland Asia, and P. t. sondaica in the Greater Sunda Islands and possibly in Sundaland.^[14]
Results of craniological analysis of 111 tiger skulls from Southeast Asian range countries indicate that Sumatran tiger skulls differ from Indochinese and Javan tiger skulls, whereas Bali tiger skulls are similar in size to Javan tiger skulls. The authors proposed to classify Sumatran and Javan tiger as distinct species, P. sumatrae and P. sondaica with Bali tiger as subspecies P. sondaica balica.^[15]
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 Chinese, Siberian and Caspian tiger populations, and P. t. sondaica comprising the Javan, Bali and Sumatran tiger populations. The authors also noted that this reclassification will affect tiger conservation management.^[16] One conservation specialist welcomed this proposal as it would make captive breeding programmes and future rewilding of zoo-born tigers easier. One geneticist was sceptical of this study and maintained that the currently recognised nine subspecies can be distinguished genetically.^[17]
In 2017, the Cat Classification Task Force of the IUCN Cat Specialist Group revised felid taxonomy and now recognizes the tiger populations in continental Asia as P. t. tigris, and those in the Sunda Islands as P. t. sondaica.^[18]
The following table is based on the classification of the species Panthera tigris provided in Mammal Species of the World.^[13] It also reflects the classification used by the Cat Classification Task Force:

Non-insular Asia

Subspecies	Description	Image
Bengal tiger (P. t. tigris) (Linnaeus, 1758)[18][13]	The Bengal tiger's coat colour varies from light yellow to reddish yellow with black stripes.[19] Males attain a total nose-to-tail length of 270 to 310 cm (110 to 120 in) and weigh between 180 to 258 kg (397 to 569 lb), while females range from 240 to 265 cm (94 to 104 in) and 100 to 160 kg (220 to 350 lb).[20][21] In northern India and Nepal, the average is larger; males weigh up to 235 kilograms (518 lb), while females average 140 kilograms (310 lb).[22] Recorded body weights of wild individuals indicate that it is the heaviest subspecies.[23] This population occurs in Bangladesh, Bhutan, India, Nepal, foremost in alluvial grasslands, subtropical and tropical rainforests, scrub forests, wet and dry deciduous forests and mangrove habitats. It is extinct in Pakistan.[1] In 2014, the population in India was estimated at 2,226 mature individuals,[24] 163–253 in Nepal and 103 in Bhutan.[25]
Caspian tiger (P. t. tigris),[18] formerly P. t. virgata (Illiger, 1815)[13]	The Caspian tiger was described as having narrow and closely set stripes.[26] The size of its skull did not differ significantly from that of the Bengal tiger.[14] According to genetic analysis, it was closely related to the Siberian tiger.[27] The population inhabited forests and riverine corridors from Eastern Anatolia, South Caucasus and coast of Caspian Sea, along the coast of the Aral Sea, in Amu-Darya and Syr-Darya basins to the southern shore of Lake Balkhash and into the Altai Mountains.[26] It had been recorded in the wild until the early 1970s and is considered extinct since the late 20th century.[28]
Siberian tiger (P. t. tigris),[18] formerly P. t. altaica (Temminck, 1844).[13] Also known as the Amur tiger.	The Siberian tiger has a thick coat with pale hues and few dark brown stripes.[26] Males have a head and body length of between 190 and 230 cm (75 and 91 in) and weigh between 180 and 306 kg (397 and 675 lb), while females average 160 to 180 cm (63 to 71 in) and 100 to 167 kg (220 to 368 lb). Tail length is about 60–110 cm (24–43 in).[20] This population inhabits the Amur-Ussuri region of Primorsky Krai and Khabarovsk Krai in far eastern Siberia, with a small population in Hunchun National Siberian Tiger Nature Reserve in northeastern China near the border to North Korea.[29][30] It is extinct in Mongolia, North Korea, and South Korea.[1] In 2005, there were 331–393 adult and subadult Siberian tigers in the region, with a breeding adult population of about 250 individuals.[31] As of 2015, there was an estimated population of 480-540 individuals in the Russian Far East.[32]
Indochinese tiger (P. t. tigris),[18] formerly P. t. corbetti Mazák, 1968[13]	The Indochinese tiger was described as being smaller than the Bengal tiger and as having a smaller skull. Males average 108 inches (270 cm) in total length and weigh between 150 and 195 kg (331 and 430 lb), while females average 96 inches (240 cm) and 100–130 kg (220–290 lb).[20] This population occurs in Myanmar, Thailand, Laos, but has not been recorded in Vietnam since 1997. In 2010, the population in Indochina was estimated at about 350 individuals. In Southeast Asia, tiger populations have declined in key areas and are threatened by illegal production of tiger bone for use in traditional medicine.[1]
Malayan tiger (P. t. tigris),[18] formerly P. t. jacksoni Luo et al., 2004	There is no clear difference between the Malayan and the Indochinese tiger in pelage or skull size.[33] It was proposed as a distinct subspecies on the basis of mtDNA and micro-satellite sequences that differs from the Indochinese tiger.[34] Males range in total length from 190–280 cm (75–110 in) and weigh between 47.2 to 129.1 kg (104 to 285 lb), while females range from 180–260 cm (71–102 in) and 24 to 88 kg (53 to 194 lb).[35] The population was roughly estimated at 250 to 340 adult individuals in 2013, and likely comprised less than 200 mature breeding individuals at the time.[36] The geographic division between Malayan and Indochinese tigers is unclear as tiger populations in northern Malaysia are contiguous with those in southern Thailand.[1] In Singapore the last tiger was shot in 1932; tigers are considered extirpated since the 1950s.[35]
South China tiger (P. t. tigris),[18] formerly P. t. amoyensis (Hilzheimer, 1905)[13]	The South China tiger is considered to be the most ancient of the tiger subspecies and is distinguished by a particularly narrow skull, long-muzzled nose, rhombus-like stripes and vivid orange colour. Males range in total length from 230–260 cm (91–102 in) and weigh between 130 to 180 kg (290 to 400 lb), while females range from 220–240 cm (87–94 in) and 100 to 110 kg (220 to 240 lb).[20] The population is extinct in the wild.[1] Despite unconfirmed reports and some evidence of footprints, there has been no confirmed sighting in China since the early 1970s.[37] As of 2007, the captive population consisted of 73 individuals, which derived from six wild founders.[38]

Sunda Islands

Subspecies	Description	Image
Javan tiger (P. t. sondaica) (Temminck, 1844)[18][13]	The Javan tiger was small compared to tigers of the Asian mainland.[20] Males weighed 100–141 kg (220–311 lb) and females 75–115 kg (165–254 lb).[33] This population was limited to the Indonesian island of Java, and had been recorded until the mid-1970s.[39] After 1979, no more sightings were confirmed in the region of Mount Betiri.[40] An expedition to Mount Halimun Salak National Park in 1990 did not yield any definite, direct evidence for the continued existence of tigers.[41]
Bali tiger (P. t. sondaica),[18] formerly P. t. balica (Schwarz, 1912)[13]	The Bali tiger was the smallest tiger and limited to the Indonesian island of Bali. It had a weight of 90–100 kg (200–220 lb) in males and 65–80 kg (143–176 lb) in females.[42] A typical feature of Bali tiger skulls is the narrow occipital plane, which is analogous with the shape of skulls of Javan tigers.[43] In Bali, tigers were hunted to extinction; the last Bali tiger, an adult female, is thought to have been killed at Sumbar Kima, West Bali, on 27 September 1937, though there were unconfirmed reports that villagers found a tiger corpse in 1963.[44]
Sumatran tiger (P. t. sondaica),[18] formerly P. t. sumatrae Pocock, 1929[13]	It is the smallest of all living tigers. Males range in total length from 220 to 255 cm (87 to 100 in) and weigh between 100 to 140 kg (220 to 310 lb), while females range between 215 to 230 cm (85 to 91 in) and 75 to 110 kg (165 to 243 lb).[20] The reasons for its small size compared to mainland tigers are unclear, but probably the result of competition for limited and small prey.[14] The population is thought to be of Asia mainland origin and to have been isolated about 6,000 to 12,000 years ago after a rise in sea-level created the Indonesian island of Sumatra.[33][45] The population is the last surviving of the three Indonesian island tiger populations. It is listed as Critically Endangered on the IUCN Red List. By 2008, the wild population was estimated at between 441 and 679 in 10 protected areas covering about 52,000 km2 (20,000 sq mi).[46]

Evolution and genetics

Tiger phylogenetic relationships

Restoration of Panthera zdanskyi, an extinct relative whose oldest remains were found in northwest China, suggesting the origins of the tiger lineage

The tiger's closest living relatives were previously thought to be the Panthera species lion, leopard and jaguar. Results of genetic analysis indicate that about 2.88 million years ago, the tiger and the snow leopard diverged from the other Panthera species, and that both may be more closely related to each other than to the lion, leopard and jaguar.^[47][48] Results of a phylogeographic study indicate that all living tigers had a common ancestor 72,000–108,000 years ago.^[34]
Fossil remains of the Longdan tiger were found in the Gansu province of northwestern China. This species lived at the beginning of the Pleistocene, about 2 million years ago, and is considered to be a sister taxon of the modern tiger. It was about the size of a jaguar and probably had a different coat pattern. Despite being considered more "primitive", the Longdan tiger was functionally and possibly ecologically similar to the modern tiger. As it lived in northwestern China, that may have been where the tiger lineage originated. Tigers grew in size, possibly in response to adaptive radiations of prey species like deer and bovids, which may have occurred in Southeast Asia during the early Pleistocene.^[49]
The earliest fossils of true tigers are between 1.6 and 1.8 million years old and were found in Java. Distinct fossils are known from the early and middle Pleistocene deposits in China and Sumatra. The Trinil tiger (Panthera tigris trinilensis) lived about 1.2 million years ago and is known from fossils found at Trinil in Java.^{[citation needed]} The Wanhsien, Ngandong, Trinil and Japanese tigers became extinct in prehistoric times.^[50]
Tigers first reached India and northern Asia in the late Pleistocene, reaching eastern Beringia, Japan, and Sakhalin. Some fossil skulls are morphologically distinct from lion skulls, which could indicate tiger presence in Alaska during the last glacial period, about 100,000 years ago.^[51] Fossils found in Japan indicate the local tigers were smaller than the mainland forms, possibly due to insular dwarfism. Until the Holocene, tigers also lived in Borneo and on the Palawan island in the Philippines.^[52]
The tiger's full genome sequence was published in 2013. It was found to have similar repeat composition than other cat genomes and an appreciably conserved synteny.^[53]

 

 

 

Hybrids

 

Further information: Felid hybrid, Panthera hybrid, Liger, and Tigon

Lions have been known to breed with tigers (most often the Amur and Bengal tigers) to create hybrids called ligers and tigons. Such hybrids were once commonly bred in zoos, but this is now discouraged due to the emphasis on conservation. Hybrids are still bred in private menageries and in zoos in China.^{[citation needed]}
The liger is a cross between a male lion and a tigress.^[54] Because the lion sire passes on a growth-promoting gene, but the corresponding growth-inhibiting gene from the female tiger is absent, ligers grow far larger than either parent species. They share physical and behavioural qualities of both parent species (spots and stripes on a sandy background). Male ligers are sterile, but female ligers are often fertile. Males have about a 50% chance of having a mane, but, even if they do, their manes will be only around half the size of that of a pure lion. Ligers are typically between 10 and 12 ft (3.0 and 3.7 m) in length, and can weigh between 800 and 1,000 lb (360 and 450 kg) or more.^[54]
The less common tigon is a cross between a lioness and a male tiger.^[55] Because the male tiger does not pass on a growth-promoting gene and the lioness passes on a growth inhibiting gene, tigons are often relatively small, only weighing up to 150 kg (330 lb). Like ligers, they have physical and behavioural traits from both parental species, and males are sterile. Females are sometimes fertile and have occasionally given birth to litigons when mated to a male Asiatic lion.^[56]

 

 

 

Characteristics

Though the tiger's skull is similar to that of the lion, the lower jaw structure is a reliable indicator of the species

The tiger has a muscular body with powerful forelimbs, a large head and a tail that is about half the length of its body. Its pelage is dense and heavy, and colouration varies between shades of orange and brown with white ventral areas and distinctive vertical black stripes that are unique in each individual.^[57][20] Stripes are likely advantageous for camouflage in vegetation such as long grass with strong vertical patterns of light and shade.^[58][59] The tiger is one of only a few striped cat species; it is not known why spotted patterns and rosettes are the more common camouflage pattern among felids.^[60] A tiger's coat pattern is still visible when it is shaved. This is due not to skin pigmentation, but to the stubble and hair follicles embedded in the skin, similar to human beards (colloquially five o'clock shadow), and is in common with other big cats.^[61] They have a mane-like heavy growth of fur around the neck and jaws and long whiskers, especially in males. The pupils are circular with yellow irises. The small, rounded ears have a prominent white spot on the back, surrounded by black.^[20] These false "eyespots", called ocelli, apparently play an important role in intraspecies communication.^[62]
The skull is similar to that of the lion, though the frontal region is usually not as depressed or flattened, with a slightly longer postorbital region. The skull of a lion has broader nasal openings. However, due to variation in skulls of the two species, the structure of the lower jaw is a more reliable indicator of the species.^[26] The tiger also has fairly stout teeth; the somewhat curved canines are the longest among living felids with a crown height of up to 90 mm (3.5 in).^[20]

Size

The Siberian tiger, the largest tiger in captivity, but not in the wild, and the tallest tiger at the shoulder, besides the Bengal tiger

The Bengal tiger

Tigers are the most variable in size of all big cat species.^[19] There is a notable sexual dimorphism between males and females, latter being consistently smaller than males. The size difference between males and females is proportionally greater in the large tiger subspecies, with males weighing up to 1.7 times more than females. Males also have wider forepaw pads than females, enabling gender to be told from tracks.^[63] Males vary in total length from 250 to 390 cm (98 to 154 in) and weigh between 90 to 306 kg (198 to 675 lb) with skull length ranging from 316 to 383 mm (12.4 to 15.1 in). Females vary in total length from 200 to 275 cm (79 to 108 in), weigh 65 to 167 kg (143 to 368 lb) with skull length ranging from 268 to 318 mm (10.6 to 12.5 in).^[64] The heaviest wild tiger ever reported had a total body length of 3.38 m (11.1 ft) over curves.^[65] In either sex, the tail represents about 0.6 to 1.1 m (24 to 43 in) of total length.^[20] Large male Siberian tigers reach a total length of more than 3.5 m (11.5 ft) over curves and 3.3 m (10.8 ft) between pegs, with a weight of up to 306 kg (675 lb). This is considerably larger than the weight of 75 to 140 kg (165 to 309 lb) reached by the Sumatran tiger. At the shoulder, tigers may variously stand 0.7 to 1.22 m (2.3 to 4.0 ft) tall.^[42] The heaviest tiger on record was a Bengal tiger shot in 1967 allegedly weighing 388.7 kg (857 lb); unverified is whether this individual had a full or empty stomach.^[66] It has been hypothesised that body size of different tiger populations may be correlated with climate and be explained by thermoregulation and Bergmann's rule, or by distribution and size of available prey species.^[20][67]
The Bengal and Siberian tigers are amongst the tallest cats in shoulder height.^[68][65] They are also ranked with the Caspian tiger among the biggest cats that ever existed.^[20] However, a wild adult male Siberian tiger at 176.4 kilograms (389 lb) body weight is outweighed by an adult, male Bengal tiger at 196 kilograms (432 lb).^[23][69]
To compare, the weight of a male Southern African lion has been indicated as 187.5 to 193.3 kg (413 to 426 lb).^[70]

Colour variations

White tigers, this recessive colour variant is found in the Bengal and Siberian tigers, and with regular stripes and blue eyes. It is not albinism.

A golden tiger, another colour variant, results in thicker light-gold fur, pale legs and faint orange stripes

A well-known allele found only in the Bengal population produces the white tiger, a colour variant first recorded in the early 19th century and found in an estimated one in 10,000 natural births. Genetically, whiteness is recessive: a cub is white only when both parents carry the allele for whiteness.^[71] It is not albinism, pigment being evident in the white tiger's stripes and in their blue eyes.^[58] The causative mutation changes a single amino acid in the transporter protein SLC45A2.^[72]
White tigers are more frequently bred in captivity, where the comparatively small gene pool can lead to inbreeding. This has given white tigers a greater likelihood of being born with physical defects, such as cleft palate, scoliosis (curvature of the spine), and strabismus (squint).^[71] Even apparently healthy white tigers generally do not live as long as their orange counterparts. Attempts have been made to cross white and orange tigers to remedy this, often mixing with other subspecies in the process.^[73]
Another recessive gene creates the "golden" or "golden tabby" colour variation, sometimes known as "strawberry". Golden tigers have thicker than usual light-gold fur, pale legs, and faint orange stripes. Few golden tigers are kept in captivity; they are invariably at least part Bengal. Some golden tigers carry the white tiger gene,^[74] and when two such tigers are mated, they can produce some stripeless white offspring. Although a "pseudo-melanistic" effect—wide stripes that partially obscure the orange background—has been seen in some pelts, no true black tigers have been authenticated, with the possible exception of one dead specimen examined in Chittagong in 1846. These wholly or partially melanistic tigers, if they exist, are assumed to be intermittent mutations rather than a distinct species.^[75][76] There are further unconfirmed reports of a "blue" or slate-coloured variant, the Maltese tiger. However, while some felids do exhibit this colouration as a solid coat, there is no known genetic configuration that would result in black stripes on a blue-gray background.^[75]

 

 

Distribution and habitat

Historical distribution

At the end of the last glacial period about 20,000 years ago, the tiger was widespread from Eastern Anatolia Region and Mesopotamia, in Central Asia to eastern Siberia and South and Southeast Asia to the Indonesian islands of Java, Bali and Sumatra.^[66] Today, tigers are regionally extinct in Afghanistan, Ukraine, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Iran, Pakistan and Singapore.^[1]
Fossil remains indicate that tigers were also present in Beringia in the north, Japan to the east, and Borneo and Palawan in the Philippines in the south, during the Late Pleistocene and Early Holocene.^{[66][51][50][77][78][79][80]}
During the 20th century, tigers became extinct in Western and Central Asia, and were restricted to isolated pockets in the remaining parts of their range. They were extirpated on the island of Bali in the 1940s, around the Caspian Sea in the 1970s, and on Java in the 1980s. This was the result of habitat loss and the ongoing killing of tigers and tiger prey. Today, their significantly fragmented and depopulated range extends eastward from India to Bangladesh, Bhutan, Nepal, Myanmar, Thailand, Cambodia, Laos, Vietnam, China, Malaysia, Indonesia, North Korea and Russia. The northern limit of their range is close to the Amur River in southeastern Siberia. The only large island they still inhabit is Sumatra.^[1] Since the beginning of the 20th century, tigers' historical range has shrunk by 93%. In the decade from 1997 to 2007, the estimated area known to be occupied by tigers has declined by 41%.^[2][81]
The tiger occupies a wide range of habitat types, but will usually require sufficient cover, proximity to water, and an abundance of prey. It prefers dense vegetation, for which its camouflage colouring is ideally suited, and where a single predator is not at a disadvantage compared with the multiple cats in a pride.^[58] A further habitat requirement is the placement of suitably secluded den locations, which may consist of caves, large hollow trees, or dense vegetation.^[82] The Bengal tiger in particular lives in many types of forests, including wet, evergreen, and the semi-evergreen forests of Assam and eastern Bengal, swampy mangrove forests of the Ganges Delta, deciduous forest in the Terai, and thorn forests in the Western Ghats. In various parts of its range it inhabits or had inhabited additionally partially open grassland and savanna as well as taiga forests and rocky habitats.^{[citation needed]}

Biology and behaviour

Tigers are comfortable in water and frequently bathe

Social and daily activities

Captive male South Chinese tiger marking his territory

Play media

A captive tiger swimming and playing with a piece of wood in a pool

Adult tigers lead largely solitary lives. They establish and maintain territories but have much wider home ranges within which they roam. Resident adults of either sex generally confine their movements to their home ranges, within which they satisfy their needs and those of their growing cubs. Individuals sharing the same area are aware of each other's movements and activities.^[76] The size of the home range mainly depends on prey abundance, and, in the case of males, on access to females. A tigress may have a territory of 20 km² (7.7 sq mi), while the territories of males are much larger, covering 60 to 100 km² (23 to 39 sq mi). The range of a male tends to overlap those of several females, providing him with a large field of prospective mating partners.^[83]
The tiger is a long-ranging species, and individuals disperse over distances of up to 650 km (400 mi) to reach tiger populations in other areas.^[84]
It is strong swimmer and often bathes in ponds, lakes and rivers, thus keeping cool in the heat of the day. Generally, among the big cat species, only the jaguar shares a similar fondness for water in the wilderness.^[85] Individuals can cross rivers up to 7 km (4.3 mi) wide and can swim up to 29 km (18 mi) in a day.^[82] They are able to carry prey through, or capture it in, the water.^{[citation needed]}
Young female tigers establish their first territories close to their mother's. The overlap between the female and her mother's territory reduces with time. Males, however, migrate further than their female counterparts and set out at a younger age to mark out their own area. A young male acquires territory either by seeking out an area devoid of other male tigers, or by living as a transient in another male's territory until he is older and strong enough to challenge the resident male. Young males seeking to establish themselves thereby comprise the highest mortality rate (30–35% per year) amongst adult tigers.^[86]
To identify his territory, the male marks trees by spraying urine^[87][88] and anal gland secretions, as well as marking trails with scat and marking trees or the ground with their claws. Females also use these "scrapes", as well as urine and scat markings. Scent markings of this type allow an individual to pick up information on another's identity, sex and reproductive status. Females in oestrus will signal their availability by scent marking more frequently and increasing their vocalisations.^[58]
Although for the most part avoiding each other, tigers are not always territorial and relationships between individuals can be complex. An adult of either sex will sometimes share its kill with others, even those who may not be related to them. George Schaller observed a male share a kill with two females and four cubs. Unlike male lions, male tigers allow females and cubs to feed on the kill before the male is finished with it; all involved generally seem to behave amicably, in contrast to the competitive behaviour shown by a lion pride.^[62] In his book Tiger, Stephen Mills describes a social eating event witnessed by Valmik Thapar and Fateh Singh Rathore in Ranthambhore National Park thus:

A dominant tigress they called Padmini killed a 250 kg (550 lb) male nilgai – a very large antelope. They found her at the kill just after dawn with her three 14-month-old cubs and they watched uninterrupted for the next ten hours. During this period the family was joined by two adult females and one adult male, all offspring from Padmini's previous litters, and by two unrelated tigers, one female the other unidentified. By three o'clock there were no fewer than nine tigers round the kill.^[86]

A Siberian tiger swimming at Wuppertal Zoo

Occasionally, male tigers participate in raising cubs, usually their own, but this is extremely rare and not always well understood. In May 2015, Amur tigers were photographed by camera traps in the Sikhote-Alin Bioshpere Reserve. The photos show a male Amur tiger pass by, followed by a female and three cubs within the span of about two minutes.^[89] In Ranthambore, a male Bengal tiger raised and defended two orphaned female cubs after their mother had died of illness. The cubs remained under his care, he supplied them with food, protected them from his rival and sister, and apparently also trained them.^[90]
Male tigers are generally more intolerant of other males within their territories than females are of other females. Territory disputes are usually solved by displays of intimidation rather than outright aggression. Several such incidents have been observed in which the subordinate tiger yielded defeat by rolling onto its back and showing its belly in a submissive posture.^[91] Once dominance has been established, a male may tolerate a subordinate within his range, as long as they do not live in too close quarters.^[86] The most aggressive disputes tend to occur between two males when a female is in oestrus, and may rarely result in the death of one of the males.^[86][91]

Young male Bengal tiger showing flehmen response while sniffing urine marking in Bandhavgarh National Park, India

Facial expressions include the "defense threat", where an individual bares its teeth, flattens its ears and its pupils enlarge. Both males and females show a flehmen response, a characteristic grimace, when sniffing urine markings but flehmen is more often associated with males detecting the markings made by tigresses in oestrus. Like other Panthera, tigers roar, particularly in aggressive situations, during the mating season or when making a kill. There are two different roars: the "true" roar is made using the hyoid apparatus and forced through an open mouth as it progressively closes, and the shorter, harsher "coughing" roar is made with the mouth open and teeth exposed. The "true" roar can be heard at up to 3 km (1.9 mi) away and is sometimes emitted three or four times in succession. When tense, tigers will moan, a sound similar to a roar but more subdued and made when the mouth is partially or completely closed. Moaning can be heard 400 m (1,300 ft) away.^[20] Chuffing, soft, low-frequency snorting similar to purring in smaller cats, is heard in more friendly situations.^[92] Other vocal communications include grunts, woofs, snarls, miaows, hisses and growls.^[20]

Hunting and diet

An adult tiger showing incisors, canines and part of the premolars and molars, while yawning in Franklin Park Zoo

Bengal tiger subduing an Indian boar at Tadoba National Park

In the wild, tigers mostly feed on large and medium-sized animals, preferring ungulates weighing at least 90 kg (200 lb).^[93][94] They typically have little or no deleterious effect on their prey populations.^[82] Sambar deer, chital, barasingha, wild boar, gaur, nilgai and both water buffalo and domestic buffalo, in descending order of preference, are the tiger's favoured prey in Tamil Nadu, India,^[93] while gaur and sambar are the preferred prey and constitute the main diet of tigers in other parts of India.^[95][96] They also prey on other predators, including dogs, leopards, pythons, sloth bears, and crocodiles.
In Siberia, the main prey species are Manchurian wapiti and wild boar (the two species comprising nearly 80% of the prey selected) followed by sika deer, moose, roe deer, and musk deer.^[97] Asiatic black bears and Ussuri brown bears may also fall prey to tigers,^[42][98][99] and they constitute up to 40.7% of the diet of Siberian tigers depending on local conditions and the bear populations.^[100] In Sumatra, prey include sambar deer, muntjac, wild boar, Malayan tapir and orangutan.^[101][102] In the former Caspian tiger's range, prey included saiga antelope, camels, Caucasian wisent, yak, and wild horses. Like many predators, tigers are opportunistic and may eat much smaller prey, such as monkeys, peafowl and other ground-based birds, hares, porcupines, and fish.^[93][58]

Bengal tiger attacking a sambar in Ranthambore Tiger Reserve

Tigers generally do not prey on fully grown adult Asian elephants and Indian rhinoceros but incidents have been reported.^[103][104] More often, it is the more vulnerable small calves that are taken.^[105] Tigers have been reported attacking and killing elephants ridden by humans during tiger hunts in the 19th century.^[106] When in close proximity to humans, tigers will also sometimes prey on such domestic livestock as cattle, horses, and donkeys.^[107] Old or wounded tigers, unable to catch wild prey, can become man-eaters; this pattern has recurred frequently across India. An exception is in the Sundarbans, where healthy tigers prey upon fishermen and villagers in search of forest produce, humans thereby forming a minor part of the tiger's diet.^[108] Although almost exclusively carnivorous, tigers will occasionally eat vegetation for dietary fibre such as fruit of the slow match tree.^[107]

Tiger dentition (above) and Asian black bear (below). The large canines make the killing bite; the carnassials tear flesh.

Tigers are thought to be mainly nocturnal predators,^[109] but in areas where humans are typically absent, they have been observed via remote-controlled, hidden cameras, hunting in daylight.^[110] They generally hunt alone and ambush their prey as most other cats do, overpowering them from any angle, using their body size and strength to knock the prey off balance. Successful hunts usually require the tiger to almost simultaneously leap onto its quarry, knock it over, and grab the throat or nape with its teeth.^[82] Despite their large size, tigers can reach speeds of about 49–65 km/h (30–40 mph) but only in short bursts; consequently, tigers must be close to their prey before they break cover. If the prey catches wind of the tiger's presence before this, the tiger usually abandons the hunt rather than chase prey or battle it head-on. Horizontal leaps of up to 10 m (33 ft) have been reported, although leaps of around half this distance are more typical. One in 2 to 20 hunts, including stalking near potential prey, ends in a successful kill.^{[82][111][112]}
When hunting larger animals, tigers prefer to bite the throat and use their powerful forelimbs to hold onto the prey, often simultaneously wrestling it to the ground. The tiger remains latched onto the neck until its target dies of strangulation.^[62] By this method, gaurs and water buffaloes weighing over a ton have been killed by tigers weighing about a sixth as much.^[113] Although they can kill healthy adults, tigers often select the calves or infirm of very large species.^[114] Healthy adult prey of this type can be dangerous to tackle, as long, strong horns, legs and tusks are all potentially fatal to the tiger. No other extant land predator routinely takes on prey this large on their own.^[115][116] Whilst hunting sambars, which comprise up to 60% of their prey in India, tigers have reportedly made a passable impersonation of the male sambar's rutting call to attract them.^[93][107]
With smaller prey, such as monkeys and hares, the tiger bites the nape, often breaking the spinal cord, piercing the windpipe, or severing the jugular vein or common carotid artery.^[117] Though rarely observed, some tigers have been recorded to kill prey by swiping with their paws, which are powerful enough to smash the skulls of domestic cattle,^[107] and break the backs of sloth bears.^[118]
During the 1980s, a tiger named "Genghis" in Ranthambhore National Park was observed frequently hunting prey through deep lake water, a pattern of behaviour that had not previously been witnessed in over 200 years of observations. Moreover, he appeared to be unusually successful, with 20% of hunts ending in a kill.^[119]
After killing their prey, tigers sometimes drag it to conceal it in vegetative cover, usually pulling it by grasping with their mouths at the site of the killing bite. This, too, can require great physical strength. In one case, after it had killed an adult gaur, a tiger was observed to drag the massive carcass over a distance of 12 m (39 ft). When 13 men simultaneously tried to drag the same carcass later, they were unable to move it.^[82] An adult tiger can go for up to two weeks without eating, then gorge on 34 kg (75 lb) of flesh at one time. In captivity, adult tigers are fed 3 to 6 kg (6.6 to 13.2 lb) of meat a day.^[82]

 

 Enemies and competitors

Tiger hunted by wild dogs (dholes) as illustrated in Samuel Howett & Edward Orme, Hand Coloured, Aquatint Engravings, 1807

Tigers usually prefer to eat prey they have caught themselves, but are not above eating carrion in times of scarcity and may even pirate prey from other large carnivores. Although predators typically avoid one another, if a prey item is under dispute or a serious competitor is encountered, displays of aggression are common. If these are not sufficient, the conflicts may turn violent; tigers may kill competitors as leopards, dholes, striped hyenas, wolves, bears, pythons, and crocodiles on occasion. Tigers may also prey on these competitors.^{[42][118][120][121][122][123]} Attacks on smaller predators, such as badgers, lynxes, and foxes, are almost certainly predatory.^[93] Crocodiles, bears, and large packs of dholes may win conflicts against tigers and in some cases even kill them.^{[42][26][124][125]}
The considerably smaller leopard avoids competition from tigers by hunting at different times of the day and hunting different prey.^[126] In India's Nagarhole National Park, most prey selected by leopards were from 30 to 175 kg (66 to 386 lb) against a preference for prey weighing over 176 kg (388 lb) in the tigers. The average prey weight in the two respective big cats in India was 37.6 kg (83 lb) against 91.5 kg (202 lb).^[127] With relatively abundant prey, tigers and leopards were seen to successfully coexist without competitive exclusion or interspecies dominance hierarchies that may be more common to the African savanna, where the leopard exists with the lion.^[127] Golden jackals may feed on the tiger's kills.^[128]

Reproduction

"Tiger cub" redirects here. For other uses, see Tiger Cub.

Wikimedia Commons has media related to Mating tigers.

A Siberian tigress with her cub at the Buffalo Zoo, New York

Two cubs playing with soccer ball at Frankfurt Zoo

Mating can occur all year round, but is more common between November and April.^[82] A female is only receptive for three to six days. Mating is frequent and noisy during that time. Gestation ranges from 93 to 112 days, with an average of 103 to 105 days. Litters consist of one or three cubs, rarely also six. Cubs weigh from 680 to 1,400 g (1.50 to 3.09 lb) each at birth, and are born blind. Females lactate for five to six months.^[57] The females rears them alone, with the birth site and maternal den in a sheltered location such as a thicket, cave or rocky crevice. The father generally takes no part in rearing them. Unrelated wandering male tigers often kill cubs to make the female receptive, since the tigress may give birth to another litter within five months if the cubs of the previous litter are lost. The mortality rate of tiger cubs is about 50% in the first two years.^[82] Few other predators attack tiger cubs due to the diligence and ferocity of the mother. Apart from humans and other tigers, common causes of cub mortality are starvation, freezing, and accidents.^[116]
A dominant cub emerges in most litters, usually a male.^[119] This cub is more active than its siblings and takes the lead in their play, eventually leaving its mother and becoming independent earlier. The cubs open their eyes at six to fourteen days old. By eight weeks, the cubs make short ventures outside the den with their mother, although they do not travel with her as she roams her territory until they are older. The cubs are nursed for three to six months. Around the time they are weaned, they start to accompany their mother on territorial walks and they are taught how to hunt. The cubs often become capable (and nearly adult size) hunters at eleven months old. The cubs become independent around eighteen months of age, but it is not until they are around two to two and a half years old that they fully separate from their mother. Females reach sexual maturity at three to four years, whereas males do so at four to five years. The oldest recorded captive tiger lived for 26 years. A wild specimen, having no natural predators, could in theory live to a comparable age.^[82]

Threats

Major threats to the tiger include habitat destruction, habitat fragmentation and poaching for fur and body parts, which have simultaneously greatly reduced tiger populations in the wild^[1] In India, only 11% of the historical tiger habitat remains due to habitat fragmentation.^[129] Demand for tiger parts for use in traditional Chinese medicine has also been cited as a major threat to tiger populations.^[130][131]

 

Commercial hunting and traditional medicine

 

Historically, tigers have been hunted at a large scale so their famous striped skins could be collected. The trade in tiger skins peaked in the 1960s, just before international conservation efforts took effect. By 1977, a tiger skin in an English market was considered to be worth US$4,250.^[82]
Many people in China and other parts of Asia have a belief that various tiger parts have medicinal properties, including as pain killers and aphrodisiacs.^[132] There is no scientific evidence to support these beliefs. The use of tiger parts in pharmaceutical drugs in China is already banned, and the government has made some offences in connection with tiger poaching punishable by death.^[which?] Furthermore, all trade in tiger parts is illegal under the Convention on International Trade in Endangered Species of Wild Fauna and Flora and a domestic trade ban has been in place in China since 1993.^[133]
However, the trading of tiger parts in Asia has become a major black market industry and governmental and conservation attempts to stop it have been ineffective to date.^[82] Almost all black marketers engaged in the trade are based in China and have either been shipped and sold within in their own country or into Taiwan, South Korea or Japan.^[82] The Chinese subspecies was almost completely decimated by killing for commerce due to both the parts and skin trades in the 1950s through the 1970s.^[82] Contributing to the illegal trade, there are a number of tiger farms in the country specialising in breeding the cats for profit. It is estimated that between 5,000 and 10,000 captive-bred, semi-tame animals live in these farms today.^{[134][135][136]} However, many tigers for traditional medicine black market are wild ones shot or snared by poachers and may be caught anywhere in the tiger's remaining range (from Siberia to India to the Malay Peninsula to Sumatra). In the Asian black market, a tiger penis can be worth the equivalent of around $300 U.S. dollars. In the years of 1990 through 1992, 27 million products with tiger derivatives were found.^[82] In July 2014 at an international convention on endangered species in Geneva, Switzerland, a Chinese representative admitted for the first time his government was aware trading in tiger skins was occurring in China.^[137]

 

 

Conservation

Main article: Tiger conservation

Tiger population status (2016)^[4]

Country	Estimate
Bangladesh	106
Bhutan	103
Cambodia	0
China	>7
India	2,226
Indonesia	371
Laos	2
Malaysia	250
Myanmar	no data
Nepal	198
Russia	433
Thailand	189
Vietnam	<5
Total	3,890

At the start of the 20th century, it was estimated there were over 100,000 tigers in the wild, but the population has dwindled outside of captivity to between 1,500 and 3,500.^[138][139] Some estimates suggest that there are fewer than 2,500 mature breeding individuals, with no subpopulation containing more than 250 mature breeding individuals.^[1] The global wild tiger population was estimated by the World Wide Fund for Nature at 3,200 in 2011 and 3,890 in 2015—Vox reported that this was the first increase in a century.^[140][141]
India is home to the world's largest population of wild tigers.^[4] A 2014 census estimated a population of 2,226, a 30% increase since 2011.^[24] In 1973, India's Project Tiger, started by Indira Gandhi, established over 25 tiger reserves in reclaimed land, where human development was forbidden. The project was credited with tripling the number of wild Bengal tigers from some 1,200 in 1973 to over 3,500 in the 1990s, but a 2007 census showed that numbers had dropped back to about 1,400 tigers because of poaching.^[142] Following the report, the Indian government pledged $153 million to the initiative, set up measures to combat poaching, promised funds to relocate up to 200,000 villagers in order to reduce human-tiger interactions,^[143] and set up eight new tiger reserves.^[144] India also reintroduced tigers to the Sariska Tiger Reserve^[145] and by 2009 it was claimed that poaching had been effectively countered at Ranthambore National Park.^[146]
In the 1940s, the Siberian tiger was on the brink of extinction with only about 40 animals remaining in the wild in Russia. As a result, anti-poaching controls were put in place by the Soviet Union and a network of protected zones (zapovedniks) were instituted, leading to a rise in the population to several hundred. Poaching again became a problem in the 1990s, when the economy of Russia collapsed. The major obstacle in preserving the species is the enormous territory individual tigers require (up to 450 km² needed by a single female and more for a single male).^[147] Current conservation efforts are led by local governments and NGO's in concert with international organisations, such as the World Wide Fund for Nature and the Wildlife Conservation Society.^[148] The competitive exclusion of wolves by tigers has been used by Russian conservationists to convince hunters to tolerate the big cats. Tigers have less impact on ungulate populations than do wolves, and are effective in controlling the latter's numbers.^[149] In 2005, there were thought to be about 360 animals in Russia, though these exhibited little genetic diversity.^[31] However, in a decade later, the Siberian tiger census was estimated from 480 to 540 individuals.

Camera trap image of wild Sumatran tiger

Having earlier rejected the Western-led environmentalist movement, China changed its stance in the 1980s and became a party to the CITES treaty. By 1993 it had banned the trade in tiger parts, and this diminished the use of tiger bones in traditional Chinese medicine.^[150] After this, the Tibetan people's trade in tiger skins became a relatively more important threat to tigers. The pelts were used in clothing, tiger-skin chuba being worn by singers and participants in horse racing festivals, and had become status symbols. In 2004, international conservation organizations launched successful environmental propaganda campaigns in China against the Tibetan tiger skin trade. There was outrage in India, where many Tibetans live, and the 14th Dalai Lama was persuaded to take up the issue. Since then there has been a change of attitude, with some Tibetans publicly burning their chubas.^[151]
In 1994, the Indonesian Sumatran Tiger Conservation Strategy addressed the potential crisis that tigers faced in Sumatra. The Sumatran Tiger Project (STP) was initiated in June 1995 in and around the Way Kambas National Park in order to ensure the long-term viability of wild Sumatran tigers and to accumulate data on tiger life-history characteristics vital for the management of wild populations.^[152] By August 1999, the teams of the STP had evaluated 52 sites of potential tiger habitat in Lampung Province, of which only 15 these were intact enough to contain tigers.^[153] In the framework of the STP a community-based conservation programme was initiated to document the tiger-human dimension in the park in order to enable conservation authorities to resolve tiger-human conflicts based on a comprehensive database rather than anecdotes and opinions.^[154]
The Wildlife Conservation Society and Panthera Corporation formed the collaboration Tigers Forever, with field sites including the world's largest tiger reserve, the 21,756 km² (8,400 sq mi) Hukaung Valley in Myanmar. Other reserves were in the Western Ghats in India, Thailand, Laos, Cambodia, the Russian Far East covering in total about 260,000 km² (100,000 sq mi).^[155]
Tigers have been studied in the wild using a variety of techniques. Tiger population have been estimated using plaster casts of their pugmarks, although this method was criticized as being inaccurate.^[156] More recent techniques include the use of camera traps and studies of DNA from tiger scat, while radio-collaring has been used to track tigers in the wild.^[157] Tiger spray has been found to be just as good, or better, as a source of DNA than scat.^[158]
The exact number of wild tigers is unknown, as many estimates are outdated or educated guesses; few estimates are based on reliable scientific censuses. The table shows estimates according to IUCN Red List accounts and range country governments dating from 2009 to April 2016.^[4]

Rewilding and reintroduction projects

Further information: Rewilding (conservation biology), Save China's Tigers, Reintroduction, and Siberian Tiger Introduction Project

In 1978, the Indian conservationist Billy Arjan Singh attempted to rewild a tiger in Dudhwa National Park; this was the captive-bred tigress Tara.^[159] Soon after the release, numerous people were killed and eaten by a tigress that was subsequently shot. Government officials claimed it was Tara, though Singh disputed this. Further controversy broke out with the discovery that Tara was partly Siberian tiger.^{[160][161][162][163]}

A rewilded South China tiger hunting blesbok in South Africa

The organisation Save China's Tigers has attempted to rewild the South China tigers, with a breeding and training programme in a South African reserve known as Laohu Valley Reserve (LVR) and eventually reintroduce them to the wild of China.^[164]
A future rewilding project was proposed for Siberian tigers set to be reintroduced to northern Russia's Pleistocene park. The Siberian tigers sent to Iran for a captive breeding project in Tehran are set to be rewilded and reintroduced to the Miankaleh peninsula, to replace the now extinct Caspian tigers.^{[165][166][167]}

 

 

 

In captivity

Tigers made to perform at Ringling Brothers and Barnum and Bailey Circus

In Ancient Roman times, tigers were kept in menageries and amphitheatres to be exhibited, trained and paraded, and were often provoked to fight humans and exotic beasts.^[168][169] Since the 17th century, tigers, being rare and ferocious, were sought after to keep at European castles as symbols of their owners' power.^[170] Tigers became central zoo and circus exhibits in the 18th century: a tiger could cost up to 4,000 francs in France (for comparison, a professor of the Beaux-Arts at Lyons earned only 3,000 francs a year),^[171] or up to $3,500 in the United States where a lion cost no more than $1,000.^[172]
China (2007) had over 4,000 captive tigers, of which 3,000 were held by about twenty larger facilities, with the rest held by some 200 smaller facilities.^[173] The USA (2011) had 2,884 tigers in 468 facilities.^[174] Nineteen states have banned private ownership of tigers, fifteen require a license, and sixteen states have no regulation.^[175] Genetic ancestry of 105 captive tigers from fourteen countries and regions showed that forty-nine animals belonged distinctly to five subspecies; fifty-two animals had mixed subspecies origins.^[176] As such, "many Siberian tigers in zoos today are actually the result of crosses with Bengal tigers."^[177]
The Tiger Species Survival Plan has condemned the breeding of white tigers, alleging they are of mixed ancestry and of unknown lineage. The genes responsible for white colouration are represented by 0.001% of the population. The disproportionate growth in numbers of white tigers points to inbreeding among homozygous recessive individuals. This would lead to inbreeding depression and loss of genetic variability.^[178]

 

 

Relation with humans

Tiger hunting on elephant-back, India, 1808

Tiger hunting

 

Main article: Tiger hunting

The tiger has been one of the big five game animals of Asia. Tiger hunting took place on a large scale in the early 19th and 20th centuries, being a recognised and admired sport by the British in colonial India as well as the maharajas and aristocratic class of the erstwhile princely states of pre-independence India. A single maharaja or English hunter could claim to kill over a hundred tigers in their hunting career.^[82] Tiger hunting was done by some hunters on foot; others sat up on machans with a goat or buffalo tied out as bait; yet others on elephant-back.^[179]

 

 

 

 

Man-eating tigers

 

Main article: Tiger attack

Wild tigers that have had no prior contact with humans actively avoid interactions with humans. However, tigers cause more human deaths through direct attack than any other wild mammal.^[82] Attacks are occasionally provoked, as tigers lash out after being injured while they themselves are hunted. Attacks can be provoked accidentally, as when a human surprises a tiger or inadvertently comes between a mother and her young,^[180] or as in a case in rural India when a postman startled a tiger, used to seeing him on foot, by riding a bicycle.^[181] Occasionally tigers come to view people as prey. Such attacks are most common in areas where population growth, logging, and farming have put pressure on tiger habitats and reduced their wild prey. Most man-eating tigers are old, missing teeth, and unable to capture their preferred prey.^[58] For example, the Champawat Tiger, a tigress found in Nepal and then India, had two broken canines. She was responsible for an estimated 430 human deaths, the most attacks known to be perpetrated by a single wild animal, by the time she was shot in 1907 by Jim Corbett.^[65] According to Corbett, tiger attacks on humans are normally in daytime, when people are working outdoors and are not keeping watch.^[182] Early writings tend to describe man-eating tigers as cowardly because of their ambush tactics.^[183]

Man-eaters have been a particular problem in recent decades in India and Bangladesh, especially in Kumaon, Garhwal and the Sundarbans mangrove swamps of Bengal, where some healthy tigers have hunted humans. Because of rapid habitat loss attributed to climate change, tiger attacks have increased in the Sundarbans.^[185] The Sundarbans area had 129 human deaths from tigers from 1969 to 1971. In the 10 years prior to that period, about 100 attacks per year in the Sundarbans, with a high of around 430 in some years of the 1960s.^[82] Unusually, in some years in the Sundarbans, more humans are killed by tigers than vice versa.^[82] In 1972, India's production of honey and beeswax dropped by 50% when at least 29 people who gathered these materials were devoured.^[82] In 1986 in the Sundarbans, since tigers almost always attack from the rear, masks with human faces were worn on the back of the head, on the theory that tigers usually do not attack if seen by their prey. This decreased the number of attacks only temporarily. All other means to prevent attacks, such as providing more prey or using electrified human dummies, worked less well.^[186]
At least 27 people were killed or seriously injured by captive tigers in the United States from 1998 to 2001.^[187][187]
In some cases, rather than being predatory, tiger attacks on human seem to be territorial in nature. At least in one case, a tigress with cubs killed eight people entering her territory without consuming them at all.^[188]

 

 

 

Cultural depictions

 


Tigers and their superlative qualities have been a source of fascination for mankind since ancient times, and they are routinely visible as important cultural and media motifs. They are also considered one of the charismatic megafauna, and are used as the face of conservation campaigns worldwide. In a 2004 online poll conducted by cable television channel Animal Planet, involving more than 50,000 viewers from 73 countries, the tiger was voted the world's favourite animal with 21% of the vote, narrowly beating the dog.^[189]

In myth and legend

See also: Tiger worship

The Hindu goddess Durga riding a tiger. Guler school, early 18th century

In Chinese myth and culture, the tiger is one of the 12 animals of the Chinese zodiac. In Chinese art, the tiger is depicted as an earth symbol and equal rival of the Chinese dragon – the two representing matter and spirit respectively. The Southern Chinese martial art Hung Ga is based on the movements of the tiger and the crane. In Imperial China, a tiger was the personification of war and often represented the highest army general (or present day defense secretary),^[190] while the emperor and empress were represented by a dragon and phoenix, respectively. The White Tiger (Chinese: 白虎; pinyin: Bái Hǔ) is one of the Four Symbols of the Chinese constellations. It is sometimes called the White Tiger of the West (西方白虎), and it represents the west and the autumn season.^[190]
The tiger's tail appears in stories from countries including China and Korea, it being generally inadvisable to grasp a tiger by the tail.^[191][192]
In Buddhism, the tiger is one of the Three Senseless Creatures, symbolising anger, with the monkey representing greed and the deer lovesickness.^[190] The Tungusic peoples considered the Siberian tiger a near-deity and often referred to it as "Grandfather" or "Old man". The Udege and Nanai called it "Amba". The Manchu considered the Siberian tiger as "Hu Lin," the king.^[63] In Hinduism, the god Shiva wears and sits on tiger skin.^[193] The ten-armed warrior goddess Durga rides the tigress (or lioness) Damon into battle. In southern India the god Ayyappan was associated with a tiger.^[194]
The weretiger replaces the werewolf in shapeshifting folklore in Asia;^[195] in India they were evil sorcerers, while in Indonesia and Malaysia they were somewhat more benign.^[196] In the Hindu epic Mahabharata, tigers are fiercer and more ruthless than lions.^[197]

In literature, art and film

See also: Bengal tiger § Literature

William Blake's first printing of The Tyger, c. 1795

In William Blake's poem in the Songs of Experience, titled "The Tyger," the tiger is a menacing and fearful animal. In Yann Martel's 2001 Man Booker Prize winning novel Life of Pi, the protagonist, surviving shipwreck for months in a small boat, somehow avoids being eaten by the other survivor, a large Bengal tiger. The story was adapted in Ang Lee's 2012 feature film of the same name. Jim Corbett's 1944 Man-Eaters of Kumaon tells ten true stories of his tiger-hunting exploits in what is now the northern Uttarakhand region of India. The book has sold over four million copies,^[198] and has been the basis of both fictional and documentary films. In Rudyard Kipling's 1894 The Jungle Book, the tiger, Shere Khan, is the mortal enemy of the human protagonist, Mowgli; the book has formed the basis of both live-action and animated films. Other tiger characters aimed at children tend to be more benign, as for instance Tigger in A. A. Milne's Winnie-the-Pooh and Hobbes of the comic strip Calvin and Hobbes, both of whom are represented as simply stuffed animals come to life.
Tiger are also mascots for various sports teams around the world. Tony the Tiger is a famous mascot for Kellogg's breakfast cereal Frosted Flakes. The Esso (Exxon) brand of petrol was advertised from 1969 onwards with the slogan 'put a tiger in your tank', and a tiger mascot; more than 2.5 million synthetic tiger tails were sold to motorists, who tied them to their petrol tank caps.^[199]
The tiger appears in heraldry but is distinct from the heraldic beast tyger, a wolflike, snouted creature which has its roots in European Medieval bestiaries.

Political symbolism

An early silver coin of king Uttama Chola found in Sri Lanka shows the Chola Tiger sitting between the emblems of Pandyan and Chera

The tiger is one of the animals displayed on the Pashupati seal of the Indus Valley Civilisation. The tiger was the emblem of the Chola Dynasty and was depicted on coins, seals and banners.^[200] The seals of several Chola copper coins show the tiger, the Pandyan emblem fish and the Chera emblem bow, indicating that the Cholas had achieved political supremacy over the latter two dynasties. Gold coins found in Kavilayadavalli in the Nellore district of Andhra Pradesh have motifs of the tiger, bow and some indistinct marks.^[201] The tiger symbol of Chola Empire was later adopted by the Liberation Tigers of Tamil Eelam and the tiger became a symbol of the unrecognised state of Tamil Eelam and Tamil independence movement.^[202]
The Bengal tiger is the national animal of India and Bangladesh.^[203] The Malaysian tiger is the national animal of Malaysia.^[204] The Siberian tiger is the national animal of South Korea. Since the successful economies of South Korea, Taiwan, Hong Kong and Singapore were described as the Four Asian Tigers, a tiger economy is a metaphor for a nation in rapid development.