Tiger - biology.

Tiger - biology. 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 now 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 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, 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 5,000 to 7,000 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. 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 eight 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. Five tiger subspecies are still living. The Amur tiger, also known as the Siberian tiger, lives primarily in the woodlands of eastern Russia. There are more than 400 Amur tigers in the wild and almost 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 about 3,000 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. About 2,000 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. Fewer than 30 South China tigers may still survive in central and eastern China, and fewer than 50 live in Chinese zoos. IV PHYSICAL DESCRIPTION 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. Steplength 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. V TIGER BEHAVIOR An adult tiger defends a large area from all other tigers of the same sex. A female's territory must contain enough prey to support herself and her cubs. A male's territory is typically larger than a female's territory--in addition to containing enough prey, the male's territory typically overlaps with those of one to seven females in order to have access to females with which to mate. Territory size among tigers varies enormously and is directly related to the abundance of large prey. Female tigers in prey-rich habitats in Nepal, for instance, defend territories averaging 20 sq km (8 sq mi). At the other extreme, females in the prey-poor Russian Far East occupy territories averaging 500 sq km (200 sq mi). Male territories in both areas are proportionately larger. Except for a mother and her cubs, and the few days that males and females come together to mate, tigers generally live and hunt alone. Although they are solitary animals, tigers communicate with other tigers in their area through a variety of methods. Roaring, for instance, broadcasts the news of a tiger's presence and warns other tigers to stay away. Tigers use scent marks by spraying urine, dropping feces, and rubbing scent glands on trees and other objects. Scent marks are often coupled with visual signposts, such as scratch marks on trees. These smells and signs are especially concentrated at territorial boundaries and they warn other tigers of the same sex to stay out of the territory or risk a fight. Marking also enables tigers to track other tigers in an area, enabling neighbors to get to know one another through these signs. For example, a female becomes familiar with the signs of other females whose territories abut hers--in many cases a neighbor may be her daughter. Males and females within an overlapping territory learn to recognize each other through these signs, and they adjust their movements to avoid being in the same area at the same time, except when mating. Tigers hunt alone, primarily between dusk and dawn, traveling 10 to 30 km (6 to 20 mi) in a night in search of prey. They specialize in killing wild boar and other swine, and medium to large deer such as red deer, chital, and sambar. In India and Nepal tigers hunt gaur, a huge wild cattle weighing up to 1,000 kg (2,200 lb). Tigers go out of their way to kill the largest prey available and only adult Asian elephants and greater one-horned rhinoceros are safe from tigers, although tigers do kill rhinoceros and elephant calves. Tigers also kill domestic animals such as cows and goats. Occasionally tigers kill people, but usually only if other prey is scarce or the tigers are too sick or injured to catch other prey. Tigers rely on stealth to stalk their prey. They use cover such as trees, tall grass, or other vegetation to hide in while they stalk prey. Habitats where forest is interspersed with small clearings are ideal. In a typical hunt, a tiger slowly and silently stalks an animal until the tiger is about 10 m (about 30 ft) away. The tiger then lunges in a lightning-fast rush to close the gap, grabbing the animal in its forepaws and wrestling it to the ground. It finally kills the animal by sinking its teeth into the animal's throat or neck. After dragging the carcass to a secluded spot, the tiger eats. A tiger consumes 16 kg (35 lbs) of meat on an average night, and returns to the carcass nightly until the meat is gone, usually in two to three days. On average, a tiger must kill about once every eight days. A female with growing cubs to feed may kill every five to six days. Catching a meal is not easy even for such a superb predator: A tiger makes a successful kill only once in every 10 to 20 hunts. VI REPRODUCTION Males can tell when a female is ready to mate by detecting changes in the smell of her scent marks. A female is receptive to a male for about three days and during this time, called estrus, the pair may copulate hundreds of times. Stimulation from copulation is necessary for a female tiger to release eggs so they can be fertilized. If a female does not become pregnant, she will return to estrus in 30 to 60 days. The time between conception and birth, known as gestation, is 100 to 112 days for tigers. Commonly two to three (rarely four or five) blind and helpless cubs are born in a secluded spot under very thick cover. Cubs weigh about 1 kg (2.2 lb) at birth. Male cubs grow more rapidly than female cubs and a large size difference between males and females is apparent by six months of age. Mothers provide all parental care for the cubs, staying with them continuously for the first few days and hunting close by for the first two months. Fathers do not help raise cubs except to keep other adult males, which may kill newborns, out of the area. Cubs nurse until they are 6 months old, but begin eating meat after six to eight weeks when their mother takes them to her kills. Gradually, through play and practice, tiger cubs learn to hunt on their own, but even at 16 months of age they are not yet very efficient hunters. As the cubs mature they spend more and more time alone, but remain in the mother's territory. They do not strike out on their own until they are 18 to 30 months of age, depending on when the mother has a new litter. Adult females can produce a litter about every two years and older cubs leave a few months after a new litter is born. Males travel widely in search of a new territory, while females may settle in a territory that borders their mother's territory or even take part of her territory. At the time that tigers leave their mother, they are nearly adult size. Males and females become sexually mature at about 36 months. An adult female may produce as many as five litters of young in her lifetime. Some males never breed, while others father many litters. VII TIGER STATUS Tigers are disappearing in the wild at an unprecedented rate. The primary threats to tigers are from human activities, including habitat destruction that results in population fragmentation and tiger poaching. Beginning early in the 20th century, Asia experienced enormous population growth. As populations expanded, farms, villages, and cities transformed once vast wilderness areas. People and their activities now dominate the landscape. Further, the forests that remain are degraded--people have scoured the area removing fodder (food for domestic livestock) and other products, including the tiger's essential prey, the deer and pigs that people prize as food as much as tigers do. Some of the places tigers could live--where enough forest still exists--are ghost towns because there is nothing left for the tigers to eat. If all the remaining 5,000 to 7,000 wild tigers lived in one continuous interbreeding population they would not be as endangered as they are. But rapid habitat loss has caused tiger populations to become fragmented into more than 160 isolated sub-populations that are scattered over Asia. On average, each of these sub-populations consists of only about 40 individuals. Such small populations, living in small areas that average less than 500 sq km (200 sq mi) in size, can suffer from chance variations in birth and death rates. For example, all cubs could be male or female, which affects healthy reproduction and over time can lead to extinction. Another problem caused by this fragmentation is inbreeding, in which close relatives mate. Inbreeding can result in genetic disorders that can lead to increased cub mortality and weakened resistance to diseases. Small populations are also vulnerable to infectious diseases and natural disasters, such as drought or fire. Any one of these events could wipe out an entire subpopulation. In animal populations with fewer than 50 reproducing females, like most of the existing tiger sub-populations, these risks become especially dangerous. Throughout most of the 20th century tigers were killed for sport hunting and to sell their body parts, including fur for the fashion industry. Today hunting tigers is illegal in most countries where the animals are found, but poachers are still killing tigers in large numbers. The poachers sell tiger body parts on the black market, particularly bones used in medicines for traditional Chinese medicine (TCM), a formalized system of health care utilizing such therapeutic treatments as herbal medicine, acupuncture, and nutrition, which is practiced by 25 percent of the world's population. VIII CONSERVATION INITIATIVES The combination of habitat loss, population fragmentation, and poaching are pushing the tiger to the brink of extinction. To protect the animal, the tiger is listed as endangered by both the United States Fish and Wildlife Service Endangered Species List and the Red List of Threatened Species compiled by the World Conservation Union (IUCN), a nongovernmental organization that compiles global information on endangered plants and animals. The tiger is protected by the Convention on International Trade in Endangered Species (CITES), which makes it illegal to trade tigers or tiger parts. Conservation organizations are working with governments to stem the trade in tiger body parts. Several nations that are markets for tiger parts, including China, Singapore, South Korea, Taiwan, and the United States, have strengthened their laws and policies to better control the trade in tiger parts. Tiger conservationists regularly meet with TCM practitioners and users to educate them about the tiger's plight. The conservationists encourage TCM practitioners to perfect substitutes for tiger bones that can be included in the official TCM textbooks that describe how to prepare and prescribe medicines. Traditionally many scientists believed that creating national parks and other protected areas for tigers would be enough to save them. Now tiger conservationists believe that to survive over the long-term, conservationists must address the types of landscapes where tigers and their prey live. Landscapes where tigers can survive must include core areas (such as national parks) where the animals are protected; buffer zones that clearly separate the protected area from farmlands and other humandominated areas; and dispersal corridors that tigers can move through freely to travel between protected areas. In addition, degraded lands need to be restored with plentiful prey animals. In order to improve the landscapes of the diverse habitats where tigers live, conservationists seek the cooperation of local villagers, helping them understand how tiger conservation can benefit the people who live near tiger habitats. In Nepal's Royal Chitwan National Park, for example, tourists come to view the largest populations of tigers and one-horned rhinoceroses in the world. Conservationists with the World Wildlife Fund (WWF) found that the money earned from ecotourism (in which tourists pay to visit areas with interesting natural and cultural features) barely trickled down to local villagers. In addition, the conservationists found that the park was too small to maintain healthy populations of tigers for more than 20 years. Degraded habitats and buffer zones surrounding the park needed restoration in order to expand the park's protected wildlife areas. Without the help of the local communities, restoration projects such as this would likely fail. Beginning in 1989, a coalition of conservationists lobbied the Nepalese government to create local village committees to assume management of the degraded lands adjacent to the park. The coalition also helped establish legislation that required 50 percent of the revenue generated by ecotourism in the park to be recycled into local communities. These initiatives combined to give local villagers a sense of empowerment--their efforts improved the tiger's habitat, and they were rewarded as revenue from ecotourism found its way into the local economies. In addition to conservation initiatives in the wild, zoos play a critical role to help the tiger's endangered status. Tigers breed readily in captivity, and several thousand live in zoos and private animal facilities. Most zoos now collaborate to manage the breeding of captive tigers in order to maintain maximum genetic diversity within the captive tiger population and to prevent any one zoo from becoming overpopulated with tigers--a situation that causes crowding and unhealthy living circumstances for the tiger. The presence of tigers in zoos helps ensure that the tiger will never become extinct, no matter what happens to tigers in the wild. In addition, tigers in zoos serve as ambassadors for wild tigers. Millions of zoo visitors first learn about these splendid predators and the dangers they face in the wild from zoos. Scientific classification: The tiger is a member of the cat family, Felidae, in the order Carnivora, class Mammalia. Its scientific name is Panthera tigris. In the past scientists have classified tigers into eight subspecies, five of which are still living. In this classification system the Amur tiger is classified as Panthera tigris altaica, the Bengal tiger is Panthera tigris tigris, and the Sumatran tiger is Panthera tigris sumatrae. The Indochinese tiger is classified as Panthera tigris corbetti, and the South China tiger is Panthera tigris amoyensis. The three extinct subspecies are the Caspian tiger, classified as Panthera tigris virgata; the Javan tiger, classified as Panthera tigris sondaica; and the Bali tiger, classified as Panthera tigris balica. Contributed By: John Seidensticker Susan Lumpkin Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.