Tiger

I

Introduction

Tiger, largest member of the cat family and the only wild cat with striped fur. Perfectly designed predators, tigers possess beauty, grace, and awesome power. Their presence in the wild, revealed by a throaty roar or a track on a dusty trail, electrifies the forest and sends shivers down the spines of all who share its space. Humans admire tigers as much as they fear them, and the animals figure prominently in Asian myths, religions, arts, and imagination. Tigers were once found throughout the forested regions of tropical and temperate Asia. Excessive hunting and destruction of tiger habitat have narrowed the tiger’s range to a few isolated patches throughout Asia. Many people have organized local and international conservation organizations to prevent tigers from becoming extinct.

Among the 36 cat species, tigers are most closely related to lions, leopards, and jaguars. These cats evolved from a common ancestor that was probably similar to modern leopards or jaguars and lived more than 5 million years ago. The earliest fossils clearly identified as those of tigers are about 2 million years old. These fossils were found in central Asia, eastern and northern China, Siberia, Japan, Sumatra, and Java. Based on fossils dating from 300,000 to 10,000 years ago, some scientists think that tigers may have ranged into present-day Alaska via the Bering land bridge that once joined Alaska and Siberia during the last glaciation in the Pleistocene Epoch. Other scientists believe that the big cat fossils found in Alaska all belong to lions.

Scientists use a variety of methods to study the behavior of tigers and track their movements. Radio tracking was first used to track tigers in Nepal in 1973. In this method, a collar with an attached radio transmitter is placed around the neck of a tiger. Scientists monitor the radio transmissions as the tiger travels, tracking the tiger’s whereabouts to learn about its range, life history, and behaviors. More recently, scientists have set up camera traps that are triggered by an infrared beam. When a tiger crosses the infrared beam, the camera snaps a shot of the tiger, recording the date and time the photograph was taken. The tiger’s unique stripes help identify the animal, and when the same animal triggers other camera traps, the photo archives enable scientists to gather information about the tiger’s movements. This method helps scientists estimate tiger numbers in the wild.

II

Range and Habitat of Tigers

Scientists estimate that at the beginning of the 20th century 100,000 tigers flourished throughout Asia, from eastern Russia and Korea through eastern and southern China, Southeast Asia, the Indian subcontinent (see India), and into Pakistan, with separate populations around the Caspian Sea and on the Indonesian islands of Bali, Java, and Sumatra. At the start of the 21st century only 3,400 to 5,100 tigers lived in the wild in just 14 Asian countries: Bangladesh, Bhutan, Cambodia, China, India, Laos, Malaysia, Myanmar (formerly Burma), Nepal, North Korea, Russia, Sumatra, Thailand, and Vietnam. Tigers are now extinct in Bali, Java, and around the Caspian Sea, and nearly so in China and North Korea. Less than 20 percent of today’s tiger habitat is located in national parks or other protected areas, which means that the majority of the areas where tigers live could be lost to other uses, such as agriculture or urbanization.

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Tigers are territorial—they live alone in large areas that they defend from other tigers. The ideal tiger territory is a large forested area with rich vegetation for cover, plentiful water to drink and cool off in, and abundant deer, swine, and other large mammals to eat. With these three essentials, tigers can thrive in diverse habitats and climates including hot, tropical rain forests in Sumatra and Southeast Asia; cool oak and pine forest in the Amur River Valley in far eastern Russia; tall grass jungles in India and Nepal; coastal mangrove forests in Bangladesh; and mountain slopes in Bhutan.

III

Tiger Distribution

In the past scientists classified tigers into subspecies based on variations in size, coat color, and striping. However, a re-evaluation of these physical characteristics and recent genetic studies show there is little reason to divide living tigers into separate subspecies. All tigers are nearly identical both genetically and physically. Some scientists suggest making a distinction between the island tigers (now found only in Sumatra) and the tigers that live in mainland Asia, since island tigers live in a different habitat without any opportunity to breed with another population of tigers. Over many generations, these isolated populations will likely evolve genetic differences from their mainland counterparts.

Although tigers are no longer classified into subspecies, many people continue to refer to tigers using their subspecies names, in part because these names refer to where the animals are found. Using this naming system, three subspecies are now extinct. The Caspian tiger once lived in Afghanistan, Iran, Turkey, and the Central Asiatic region of Russia; it became extinct in the 1950s. The Javan tiger once lived on the island of Java and became extinct in the 1970s. The Bali tiger lived on the island of Bali; the last wild Bali tiger was killed in the late 1930s.

Six tiger subspecies are still living. The Amur tiger, also known as the Siberian tiger, lives primarily in the woodlands of eastern Russia. There are probably less than 400 Amur tigers in the wild and about 500 in zoos in Russia, Europe, and the United States. The Bengal or Indian tiger primarily lives in India, with some animals found in nearby Nepal, Bangladesh, Bhutan, and Myanmar. There are less than 2,500 Bengal tigers in the wild and about 330 in zoos, mostly in India. About 500 Sumatran tigers are found only on the island of Sumatra; another 200 live in zoos throughout Indonesia, North America, Europe, and Australia. Less than 2,500 Indochinese tigers live primarily in the remote mountainous forests of Thailand, as well as in Myanmar, southern China, Cambodia, Laos, Vietnam, and Malaysia; about 60 live in zoos in Asia and the United States. Malayan tigers are found in Malaysia, where there are likely no more than 750 remaining; more than 40 live in zoos around the world. The South China tiger is probably extinct in the wild but about 70 live in zoos, almost exclusively in China. Programs have been developed to reintroduce the South China tiger into the wild.

IV

Physical Characteristics of Tigers

Tigers typically reach a shoulder height of 1 m (3 ft) and measure from 2 to 3 m (7 to 10 ft) from head to rear end. The thick, furred tail extends about 1 m. Tigers range in size from the small Sumatrans, in which females weigh 75 to 110 kg (165 to 240 lb) and males weigh 100 to 140 kg (220 to 310 lb), to the largest Bengal tigers, in which females weigh 100 to 160 kg (220 to 350 lb) and males weigh 180 to 258 kg (400 to 570 lb). However, scientists do not consider weight a good measure of size because there can be great variation depending on environmental factors. Instead, scientists examine skull length and the crown length of the upper premolar. By these measures the largest known male and female Bengal tigers are slightly larger than the largest known Siberian tigers. The largest tigers are the largest of all cats, but since there is much variation in tiger size, some lions are bigger than some tigers.

Tiger fur is short and varies in color from dark orange to reddish brown, with creamy white on the belly, neck, and inside of limbs. Dark brown or black stripes run vertically across the body. Stripe patterns are unique to individual tigers, and like fingerprints in humans, stripes can be used to tell tigers apart. When you see a tiger in the open, its coloration is vivid and striking. But in the dappled light of the forest or in tall grass, the same bold colors make the tiger nearly invisible to prey and to people. The white tigers seen in some zoos are the result of a rare genetic mutation that occurs rarely in the wild. In the past, many zoos interbred tigers that had this gene mutation for whiteness in order to produce more white tigers. These unusual animals were very popular with zoo visitors. Today few zoos still perform this type of breeding since it serves no conservation purpose for a species that is in danger of extinction.

As carnivores that kill and feed entirely on the flesh of other mammals, tigers have short, powerful jaws with large jaw muscles. They have 30 teeth, 15 on each side of the jaw. Tigers use their large piercing canines to grab and kill prey. Their scissor-like molars slice flesh, and small incisors scrape meat from bones. Like all cats, tigers have a simple digestive system designed to process meat so that the nutrients can be readily absorbed into the bloodstream.

With the exception of white tigers, which have blue eyes, all tigers have yellow eyes. Tigers mainly use vision to find prey. Although tigers see about as well as humans during the day, their large eye openings gather more light than do human eyes, making tiger night vision far superior to that of humans. In addition, a special structure in the tiger’s eye, called the tapetum lucidum, reflects light, making objects appear brighter. Like the eyes of most carnivores, a tiger’s eyes are at the front of the face, giving tigers binocular vision so that they can focus both eyes on a single object. This helps them judge distance accurately, an ability that is important to predators that must secretly approach their prey to just the right distance before charging in for the kill.

Studies suggest that tigers have very good hearing. They can turn their ears toward the source of a sound, enhancing their hearing sensitivity. They also use olfaction (the sense of smell) to hunt prey, but smell is primarily used to communicate with other tigers in an area. The olfactory system receives smell information through the nose, but tigers also have a vomeronasal olfactory system in which smell information reaches the brain through two tiny openings in the roof of the mouth, just behind the upper incisor teeth.

The skeleton and muscles of a tiger are designed for efficient movement to catch and kill prey. Tigers have relatively long legs, giving them a long step-length (the amount of ground covered with each step). Their stance, in which the feet remain elevated and only the toes touch the ground, gives extra length to each step. Step-length is also increased by the position of the shoulder blades on the sides of the body, rather than on the back (as in humans), so the shoulders “swing” with the legs, extending the stride.

Tigers have flexible spines. During a high-speed chase, the belly muscles tighten, making the spine arch like a bow. When the muscles relax, the cat has explosive power for the next step. A long, flexible tail acts like a rudder to improve balance.

Five soft pads on the bottom of tiger paws produce a distinctive paw print, or pug mark. The padding on the bottom of the paw enables tigers to move silently. To keep their long claws sharp, tigers retract their claws into the feet until they are needed. A springlike ligament extends the claws like a switchblade.

Tigers can live up to 20 years in zoos and up to 15 years in the wild. Most wild tigers do not live that long, however. Cubs may die in floods or fires, be killed by predators or other tigers, or succumb to disease. Only half of all cubs survive to the age where they become independent of their mother. Only 40 percent of these survivors live to establish a territory and begin to produce young. Among these territorial adults, the risk of death remains high. Males typically do not live as long as females because they are more likely to engage in violent fights with other tigers to protect their territories. Adult tigers also suffer from parasites and disease, they may be injured or killed by a blow from a prey animal’s flailing hoof, or they may starve when prey is scarce. In addition, humans extensively hunt tigers.

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