Biology Term Paper

– Tigers Essay, Research Paper

The tiger is part of the kingdom Animalia, phylum Chordata, class Carnivora, family Felidae, subfamily Panthernae, genus/species Panthera tigris. Tigers have round pupils and yellow irises

(except for the blue eyes of white tigers). Due to a retinal

adaptation that reflects light back to the retina, the night vision of

tigers is six times better than that of humans. Like domestic

cats, tiger claws are retractable. Tiger scratches on trees serve

as territorial markers. No one knows exactly why tigers are

striped, but scientists think that the stripes act as camouflage (See diagram A), and help tigers hide from their prey.

The Sumatran tiger has the most stripes of all the tiger subspecies, and the Siberian tiger has the fewest stripes. Tiger stripes are like human fingerprints; no two tigers have the same pattern of stripes. The tiger’s head often carries the Chinese mark of wang or king on the forehead. Most tigers have an orange coat with dark brown or black stripes accented with white. Tigers that live in cold climates (Siberian tigers) have thicker fur than tigers that live in warm climates. A tiger’s tail is 3 to 4 feet long, about half as long as its body. Tigers use their tails for balance when they run through fast turns. They also use their tails to communicate with other tigers.

Where did tigers come from? Tigers (and all other carnivores) are descended from civet-like animals called miacids that lived during the age of the dinosaurs about 60 million years ago. These small mammals, with long bodies and short flexible limbs, evolved over millions of years into several hundred different species, including cats, bears, dogs and weasels. Approximately 37 cat species exist today, including Panthera tigris, the tiger. Tigers evolved in eastern Asia, and while some of the earliest tiger fossils have been found in Siberia and China, the tiger’s exact place of origin is unknown.

Adult tigers are solitary animals that establish their territories in areas with enough prey, cover and water to support them. The difficulty of locating prey in tiger habitat makes it more efficient for tigers to hunt alone. As a result, they do not tend to form social groups like lions. A female tiger and her cubs are the exception to this. The territory of a tiger usually ranges in size from about 26-78 sq. km, although the territory of a Siberian tiger may be as large as 310 sq. km. The size of a tiger’s territory depends on the amount of prey available. Tiger territories are not exclusive. Several tigers may follow the same trails at different times, and a male’s territory usually overlaps those of several females. Both male and female tigers spray bushes and trees along their route with a mixture of urine and scent gland secretions. This is a way of declaring their territory. They also leave scratch marks on trees, and urinate or leave droppings in prominent places.

Female tigers called tigresses reach maturity when they are about 3 years old, males a year or so later. In temperate climates, a tigress comes into estrus only seasonally; however in tropical climates, she may come into estrus throughout the year. She signals her readiness with scent markings and locating roars. The brief act of copulation occurs continually for a five day period. Tigers are induced ovulators, and must be stimulated through frequent copulation in order to become pregnant. To help stimulate ovulation, the male tiger’s penis has spines. This explains in part why the female roars and lashes out at the male immediately following copulation. Following mating, the gestation period for tigers is approximately 103 days. The average litter size of tigers is 2 or 3 cubs, the largest is 5. One usually dies at birth. Tiger cubs are born blind and weigh only about 1 kg, depending on th subspecies. They live on milk for 6-8 weeks (See diagram B) before the female begins taking them to kills to feed. Tigers have fully developed canines by 16 months of age, but they do not begin making

their own kills until about 18 months of age. Young tigers live with their mother until they are two to three years old, then they find their own territories. Females tend to stay closer to the mother’s range than males.

Over much of the tiger’s broad geographic range, wild pig, wild cattle and several species of deer are its major prey. All prey are forest or grassland ungulates that range in size from 30-900 kg. Tigers are ambush hunters, stalking their prey, approaching as closely as possible, and then charging the animal from behind. They usually bite the neck or throat of their prey. The neck-bite, which severs the spinal cord, is typcially used on small or medium sized prey, while the throat bite, which causes suffocation, is used on larger animals. After killing their prey, tigers drag the animal to a safe place, consuming it over the course of several days. Typically, wild tigers gorge themselves on fresh kills, and can eat as much as 18 kg of meat at one time. Several days may pass before they are hungry enough to hunt again.

The life span of tigers in the wild is thought to be about 10 to 15 years. Tigers in zoos live to be between 16 and 20 years old. Tiger hair length varies geographically. In the southern subspecies the hairs are short, approximately 7 to 20 mm on the back and 15 to 35 mm on the stomach. The Siberian tiger has longer hair especially in the winter, approximately 40 to 60 mm on the back and 70 to 105 mm on the stomach. The density of fur is dependent on seasonal and geographical factors. The Sumatran tiger has approximately 1,700 to 2,000 hairs per square centimeters while the winter coat of the Siberian tiger has as many as 3,000 to 3,300 hairs per square centimeter. A tiger’s forefeet have five toes and the hind feet have four toes. All toes have claws. The claws are 80 to 100 mm in length. Tigers have large teeth. The length of the canine teeth can be between 74.5 to 90 mm.

Siberian tigers are the heaviest subspecies at 225 or more kg with males heavier than females. The lightest subspecies is the Sumatran; males weigh about 110 kg and females around 90 kg. Depending on the subspecies, the head-body length of a tiger is about 1.4-2.8m. The length of the tail is 90-120 cm. The foot pads vary in size with age, resulting in inaccurate estimates when used in censusing wild populations. The heaviest tiger recorded in the Guinness Book of World Records is a 1,025-pound male Siberian tiger.

Most Bengal (Panthera tigris tigris) tigers (See

diagram C) live in India, and some range through

Nepal, Bangladesh, Bhutan, and Myanmar. The

estimated wild population is approximately 3,060-

4,735 tigers, with about 333 in captivity, primarily in

zoos in India. White tigers are simply a color variant

of Bengal tigers and are rarely found in the wild.

The distribution of the Indochinese (Panthera tigris corbetti) tiger (See diagram D) is centered in Thailand, and it is also found in Myanmar, southern China, Cambodia, Laos, Vietnam, and peninsular Malaysia. An estimated 1,180-1,790 Indochinese tigers are left in the wild, and about 60 live in zoos in Asia and the U.S.A.

The Siberian (Panthera tigris altaica) or Amur

tiger (See diagram E) lives primarily in eastern

Russia, and a few are found in northeastern China

and northern North Korea. It is estimated that 437-

506 Siberian tigers still exist in the wild. About 490

captive Siberian tigers are managed in zoo conservation programs.

The Sumatran (Panthera tigris sumatrae) tiger is found only on the Indonesian island of Sumatra. About 400-500 wild Sumatran tigers are believed to exist, primarily in the island’s five national parks. Another 235 Sumatran tigers live in zoos around the world.

The South China (Panthera tigris amoyensis) tiger is the most critically endangered of all tiger subspecies. Found in central and eastern China, it is estimated that only 20-30 South China tigers still exist in the wild. Currently 48 South China tigers live in 19 zoos, all in China.

Three tiger subspecies are considered to have become extinct in the past 70 years, the Caspian tiger, the Javan tiger and the Bali tiger.

The Caspian tiger, Panthera tigris virgata, (See diagram F) once ranged in Afghanistan, Iran, Turkey, Mongolia, and the Central Asiatic area of Russia and probably went extinct in the 1950s. The Javan tiger, Panthera tigris sondaica, formerly ranged on

the Indonesian island of Java and was last seen in 1972. The Bali tiger, Panthera tigris balica, once lived on Bali, where the last tiger was believed to have been killed in 1937.

At the beginning of this century it is estimated that there were 100,000 wild tigers, today the number is less than 8,000. Simply put, tigers are disappearing in the wild. The main threats to tigers are poaching and habitat loss. (See table A)

Even though it is illegal to kill a tiger, wild tigers are still being poached today because their bones, whiskers and other body parts can be sold on the black market for a lot of money. (See diagram G) Tiger parts are used in traditional Chinese medicine because some people believe that tiger parts have special powers. Forestry and wildlife departments are too understaffed and under budgeted to be effective against the onslaught of poachers. While the exact number of tigers being poached is unknown, some sources have estimated that one tiger a day is being killed in India.

Table A

Status of the Tiger in 1997

Tiger Sub-species Minimum Maximum

BENGAL (INDIAN) TIGER

P.t. tigris (Linnaeus 1758) 3,060 4,735

Bangladesh 300 460

Bhutan 50 240

China 30 35

India 2,500 3,750

Myanmar Present

Nepal 180 250

CASPIAN (HYRCANIAN/TURAN) TIGER

P.t. virgata (Illiger 1815)

Formerly Afghanistan Iran Chinese and Russian Turkestan Turkey EXTINCT 1970s -

SIBERIAN (AMUR/USSURI/NORTH-EAST

CHINA/MANCHURIAN) TIGER

P.t. altaica (Temminck 1844) 437 506

China 12 20

Korea (North)