Polar Bear Report

Polar Bear (Thalarctos Maritimus)

Conception

After trailing behind the Female Polar Bear for about two months the male Polar Bear then mates with the female Bear. Females are induced ovulators, which means the act of mating causes a female to release an egg for fertilization (polar bears alive). Fertilization takes place internally. Several days of mating interactions may be required to stimulate ovulation and guarantee fertilization of the egg. In doing so it starts the gestation period.

Gestation Period

The total gestation period is about eight months. During gestation the fertilized egg divides into a hollow ball of cells one layer thick, then the ball stops growing and lies free floating in the uterus for about four months. The cells then implant in the uterine wall and continue to develop (Sea World). Delayed implantation assures that the cub is born during the best time of the year for survival and allows the female to get into good physical condition and uses her energy for nursing her new born cubs (Sea World). The actual embryonic development is estimated to be four months (Smithsonian Institution).

Birth

Most adult females give birth once every three years. Sea World states, that at birth polar bear cubs weigh about 454 to 680g and are about 30cm long, however, Bears Den states that at birth the young weigh about 450g. The fur is fine at birth, making the cubs look hairless (Sea World).

Female polar bears go through a period called Denning when they are pregnant, in which they begin depositing fat. They need to gain at least 441 pounds while pregnant. (World book encyclopedia). Usually they dig dens in snowdrifts on southern facing slopes. Some dig earthen dens that later become covered by snow. Most dens are on land within 10 miles of the coast. In some areas dens are more than 62 miles from the coast. Dens can average to about 1,800ft above sea level (National Geographic). The Den is used for nursing the babies in the cold air temperatures. Because of body heat and snow insulation, the den stays warmer than the outside temperature.

Maturation

Cubs stay with their mothers for about 2 years, although some may be weaned at 1.3 years and others stay as long as 3.3 years (Sea World). They open their eyes within the first month and in about two months they begin walking. By this time they have thick, whitish fur and their teeth have almost completely grown in.

In about March or April the mother and cubs come out from the den, the cubs now weighing 20-40 pounds. The mother and cubs remain around the den for about 12 more days (Sea world). The cubs then begin eating solid food when the mother makes the first kill on the sea. The cubs grow quickly on their mother s fat rich milk and seal blubber. By eight months of age, they weigh over 99 pounds (national geographic).

Polar bear cubs learn to hunt by watching their mother. Cubs will try hunting in their first year (Bears Den). When they are about 30 months old, a female polar bear is ready to breed again and a adult male may begin following her (Sea World).

Adulthood

Female Polar Bears reach sexual maturity at about 4 years old. Male Bears reach their sexual maturity at 6 years old (Bear Den). However, most male Polar Bears don t mate until 8 to 10 years and older. They grow two to three times the size of female polar bears (World Book). Sea World states that Boars (another name for Male polar bears) weigh between 772-1,433 pounds and can get to about 8-10ft long. Sows (another name for female Polar Bear) weigh about 331-551 pounds and are 6-9ft long. Bears Den states that a full-grown Polar bear may be as much as 9.5ft long and weigh about 1,000 pounds, with an extreme of 1,600 pounds.

Compared to other bears, Polar Bears have elongated bodies and long slender necks. They can vary from pure white to light brown fur, depending upon the season, angle of light, and living environment.

Aggression

Aggression occurs between males during the breeding season. Before a Polar Bear gets to mate with the female it must fight against the other male Polar Bears to determine whose going to mate with her. Aggression also occurs when males attempt to steal food from another family of Polar Bears. If they are caught there can be many battles between them. Humans may encounter polar bears wherever human and polar bear habitats overlap. Polar bear attacks occur most often at sites of human habitation, such as hunting camps, weather stations, and towns. Compared to other bears, polar bears are more willing to consider humans as prey. (Polar bears alive). Adult polar bears have no natural predators. Males occasionally kill other males competing for mates. Males periodically kill females protecting cubs. Cubs less than one year old sometimes are prey to adult male polar bears and other carnivores, such as wolves. Malnourished mothers may cannibalize newborn cubs (Sea World).

Mating Behavior

Polar Bears mating takes place in April and May. They don t change color nor do any dances as a result of mating. Male polar bears have been seen following the tracks of breeding female polar bears for more than 62 mi. Scientists are uncertain what signals males use to track breeding females (Smithsonian Institute). Females are attracted to Males by the aggressive behavior they have during breeding season. The toughest male out of the battling males is the Bear the female is attracted to the most after battle (World Book).

Feeding Behavior

A polar Bears stomach can hold an estimated 15% to 20% of its body weight. It can digest 84% of the protein and 97% of the fats it eats (Sea World). They mainly eat seals. A seal weighing 121 pounds could provide up to eight days of energy for a Polar Bear (Bears Den). They use a method called still hunting, in which they remain motionless beside a breathing hole waiting for a seal to surface. The Polar Bear then bites onto the head or upper body and then flips it onto the ice. They also stalk food on land and in water. These methods are called aquatic stalk and land stalk. Once a seal is captured the Polar Bear bites the seals head several times before dragging it from the water to feed. They eat the skin and fat first followed by the meat. They then leave the remaining carcass on the ice for it to rot or for another animal to feast.

Disease

Polar Bears don t have many diseases; however, I found a few diseases that Polar Bears can get. One of them is Parasitic Worm Trichinella. The illness begins when the infectious cysts are eaten with the flesh of any meat-eating animal. The cysts are digested and then released and the Larvae then invade the small intestine. The female then hatches larvae that are carried by the blood and lymph to the muscles. The following can happen during the process, diarrhea, nausea, abdominal cramps, fever, muscle pain, and swelling.

Death

Polar Bears can live 20 to 30 years, but only a small proportion of Polar Bears live past 15 to 18 years.

Starvation is the greatest threat to Polar Bears. Many times larger Polar Bears chase away the older Polar Bears. In doing so, the older Polar bears starve to death. If a polar bear gets sick they may not be able feed themselves and many times they die.

Environmental threats are a huge threat to Polar bears also. Oil spills and Toxic waste causes a threat to many of them. Human-made toxic chemicals such as polychlorinated biphenyl s (PEB S), dichlorodiphenyltrichloroethane (DDT), and Chlordane s (Sea World).

Some Polar Bears die during the hunt of food or fighting during the breeding period.

Other Facts

Their body temperature, which is normally 37C (98.6F), is maintained through a thick layer of fur, a tough hide, and an insulating layer of blubber. This excellent insulation keeps a polar bear warm even when air temperatures drop to -37C (-34F). Polar bears usually swim under water at depths of only about 9.8-14.8 ft. They can remain submerged for as long as two minutes (Sea World).

1. The Oldest known Polar Bear in the Arctic lived 32 years (Bears Den)

2. The Oldest known Polar Bear in a zoological park lived 41 years (Sea World)

3. The largest Polar Bear ever recorded was a male weighing 2,209 pounds, it was 12ft long (Bears Den)

Bibliography

1. Sea World, Inc. 1997

http://www.seaworld.org/polar_bears/pbindex.html

2. Smithsonian Institution 1997

http://www.mnh.si.edu/artic/html/polar_bear.html

3. The Bear Den

http://www.nature-net.com/bears/polar.html

4. Polar Bears Alive

http://www.polarbearsalive.com

5. National Geographic January 1998 issue

Polar Bears

6. World Book Encyclopedia 1990

Chicago World Book-Childcraft international, Inc