LS150 Essentials of Biology, Dr. Francis
March 10, 2019
Throughout the Arctic region, blending into the ice and snow with their thick coats of white fur live the giant Polar Bears. These animals dominate the region at the top of the food chain. They have no natural predators and are generally unafraid of their one unnatural predator, humans. Their binomial name is Ursus maritimus, but they are more commonly called polar bears, great white northern bears, white bears, sea bears, or ice bears (Britannica). Their taxonomy classification is Kingdom Animalia, Class Mammalia, Order Carnivora, Suborder Caniformia, Family Ursidae, Genus Ursus. The genus Ursus also includes black bears, brown bears (Polar Bear Scientific Name). Unlike these other bears however, polar bears are considered a marine mammal because of the amount of time they spend in the water and on the ice pack of the Arctic. While at the top of the food chain, these polar bears do not exist without struggle. Changing climates have affected their living and hunting grounds, causing them to need to adapt. Because of ongoing and potential loss of their sea ice habitat resulting from climate change, polar bears were listed as a threatened species in the US under the Endangered Species Act in May 2008 (Polar Bear. WWF). The loss of their sea ice habitat is truly the biggest current threat to these beautiful animals.
Male polar bears can weigh more than 1300 lbs. and can be as tall as 5.5 ft. at the shoulder when standing on all four and 8 ft. when standing erect. Females come in at about half that size at around 650 lbs. (Burnie, 268). Polar bears exhibit sexual dimorphism, but only in the characteristic of their size. Their stature is longer and narrower than most other bears, making it easier for them to reach down into holes 6 ft. deep to catch prey. They have very dense fur which serves to keep their skin dry while in the water and insulate them from the cold air of the region. Its actually a two-layer coat made up of an outer layer of hollow guard hairs which help with circulation and waterproofing. Also, these hairs are pigment free and transparent which scatters and reflects light, giving them their white appearance. What you cant see is that the skin underneath all that fur is actually black, allowing them to absorb warmth from the sun. Underneath their fur and skin is a thick layer of blubber. This fat layer can be as thick as 4 inches and makes up about half of their body weight. This blubber is used as insulation, a flotation device, and energy storage during times of limited food supply or denning for the females. A polar bears feet are actually quite large in comparison to their body, but this allows them to spread their weight out over a larger surface, and the fur on them helps with traction on ice. Those paws also have long, non-retractable claws used for getting around, digging in the ice, and catching and eating their prey. Their nose is actually amazingly designed for hunting. A polar bear can catch the smell of a seals breathing hole from about 1.6 km. and through close to a meter of snow. A seal laying on the open ice can be sniffed from as much as 32 km. away! Acting much like a hunting dog, a polar bear can literally follow its nose to prey. The elongated snout also helps the animal to warm and moisten dry air before it reaches the lungs. Their eyes are dark and covered with a protective membrane to help them see well even in an environment that has a constant glare from the light on the snow. Their ears are small and rounded which helps keep the water out while swimming and they hear as well as we do. Their mouth is full of 42 teeth perfectly suited to tear through the rough hides and blubber of prey like seals. And their stomach is perfectly suited to eating that high fat blubber and protein their entire lives. (Anatomy and Physiology) It is amazing to study these bears from head to toe and realize that each and every part of their body is perfectly suited to the harsh environment in which they live. It points to intelligent design in my opinion!
Another part of this bear that amazes me is the reproductive system. The unique ways that God designed them to be fruitful and multiply are fascinating. Polar bears are mainly solitary animals until the time for breeding. Males will compete for the right to mate with a female becoming aggressive and violent. It is interesting that the older males tend to win out over the younger, stronger males simply due to their skill. In spite of this, females can and do mate with more than one male, resulting in cubs in the same litter being fathered by different males (Polar Bear Reproduction). Mating for these bears occurs in the spring (around March), but the females body is able to delay implantation as far away as October. This allows her time to build up the fat storage needed for the long hibernation period that comes with pregnancy, birth, and nursing cubs. She will gain up to 500 lbs. in this time. Including this delayed implantation, the gestation period can last from 105-265 days (Britannica). Females give birth to one to four cubs. Two used to be the most common, but more and more often they are giving birth to one. This may be due to the climate changes, food shortages, etc. These cubs are born during a period often called denning which means she is in hibernation from around October until a few months after the birth. Only pregnant females will hibernate. They give birth on land, in the den they create for that purpose. Cubs weigh less than 2 lbs. at birth, which is tiny compared to the huge creatures they will be in adulthood. The mother will live off her fat reserves until the cubs reach around 35 lbs. and they emerge together from the den. They continue to nurse until they are around 2.5 years old. In response to the harsh environment, starvation, and predators (including other male polar bears), about 60% of cubs die before reaching adulthood (Polar Bear Reproduction). The mother will teach the cubs how to survive and hunt during that 2.5 years so that they can eventually survive on their own. Cubs will remain with the mother until they reach sexual maturity. Females will have their first cub somewhere between 4 and 8 years of age and will breed every 2-3 years, producing somewhere around 12 cubs over her lifetime (Lynch, Wayne). Males reach sexual maturity around the same time as females but begin mating a bit later, likely due to the need to hone their skill of fighting for the right to breed with a female (Britannica). Without premature death, a polar bear will live in the wild for 25-30 years.
Hunting is something these bears will spend their whole life doing. They will be taught how by their mother and their survival depends on their skill. The peak hunting season for these bears is from March to July, which also happens to be the seal birthing season. At this time there is an abundance of young seals who arent yet smart enough to avoid this predator. During this time, a bear may consume as much as 70% of its needed food energy for the year! (Lynch, Wayne). When hunting is good, and food is plentiful, and adult polar bear will feed on just the blubber of its prey. The young cubs, or underfed adults will also consume the meat. When just the blubber is consumed, the rest of the carcass is left for scavengers to feed on as the bear moves on to find another target. Polar bears will travel large distances to find food, creating home ranges as large as 104 sq. miles (Lynch, Wayne). Polar bears are almost completely carnivores, and their favorite meat is that of the seal, especially the ringed seal. The bears will stalk their prey on the ice and even lie on the ice at a breathing hole waiting for the seal to emerge, sometimes waiting for hours without making a sound. As stated earlier, they can smell their prey from far away. Ringed seals will often stay under the ice, so this bears keen sense of smell is a key to its hunting. These bears are skillful and strategic hunters. They can swim or walk on the ice towards prey, often undetected until they are close enough to charge. They must be cautious because the seal has an acute sense of smell as well! When they can get within about 40 ft. of a seal undetected, they will sprint the final distance for the catch. During seal-pup season these bears will often target the birth lairs of these seals hoping for an easy target. Between their teeth and their claws, tearing into their prey is easy work once they catch it. The polar bear has an intuitive metabolism that allows them to survive whether they are in a feast or famine period. When there is plenty of food and they can eat all they want, they eat and store fat efficiently. This animal can consume 10% of its body weight in just 30 minutes. During seasons of famine, they can actually slow their metabolism to conserve fat stores and energy. They even have the capability to go into a state of walking hibernation since they dont truly hibernate (unless pregnant). This state means that their body lives off of fat reserves and recycle nitrogen. During this state they dont need to urinate so they can even conserve water. This allows them to maintain their muscle mass and body temperature and still remain slightly active. They can go several months without food if needed (The School: Polar Bear Adaptations for Hunting). When seals cannot be caught, polar bears will also eat sea birds and their eggs, whale carcasses, and an occasional walrus if theyre lucky. The ringed seal probably makes up about 70% of their diet. The polar bear spends most of its time in pursuit of food. During hunting season, polar bears tend to sleep more during the day than at night because seals are more active at night. However, we must remember that day and night in the Arctic is somewhat ambiguous. Polar bears will sleep about 7-8 hours a day, much like humans. And, also like humans, the do like to nap occasionally and will do so almost anywhere and anytime. Napping is most likely to follow the eating of a delicious meal (Behavior).
While polar bears are predominately solitary animals, there are times when they necessarily interact with each other. These times are mating seasons, and when the young cubs are together with their mother. Other interactions are less friendly such as two males fighting over a female, or a male rushing a mother with cubs because he sees them as a threat. Sometimes these bears will actually play with each other. You can see this among siblings and mating pairs. They do this by standing on their hind legs, paws hanging at their sides and wagging their heads back and forth. Their play consists of fighting and wrestling, tumbling around in the snow, which for siblings is important training for future survival. Bears will sometimes touch noses in some type of greeting, or when asking to share food. The interaction between mothers and babies is fascinating. A mother who is worried for her cubs safety will make loud sounds called chuffing, seeming to call for their whereabouts. If those cubs are misbehaving she will scold them with growls and gentle cuffs, often knocking them over. She will growl to warn them of danger or correct behavior. Loud roars, growls, hissing and snorting are signs of aggression and another bear will either choose to fight or to retreat. A common sign of retreat is to move downwind from the dominant bear, signifying submission to their authority. When charging another bear, the polar bear will drop its head and put its ears back and growl and hiss. When observed, these bears can seem rather social, but they dont spend much of their time in the company of other polar bears. (Behavior)
Polar bears are only found in the Arctic and tend to be close to the edges of packed ice where there is water, and thus seals. There are about 19 subpopulations of polar bears and currently one is in significant deline (Southern Beaufort Sea). (Polar Bear WWF). Some things that have threatened these amazing creatures are similar to threats for other animal populations. They are very curious by nature and will consume things like trash, plastics, and chemicals if they find them. While there are not too many people populations in the Arctic there are things like tourist operations, shipping yards and some factories that pose risk. Another problem is oil spills. Even if they happen very infrequently, the effects can be felt for long afterwards, affecting not only the polar bears, but other animal populations as well. The polar bears depend on sea animals for food, so an oil spill that harms or kills off populations of whales, walrus, seals, etc. can have a powerful impact on the polar bear as well. The oil can also make it hard for the bears to swim, get caught in their thick coats, and the smell of the oil can impact their ability to smell prey as effectively. In order to clean their fur (or the fur of their young) of the oil, they will spend long periods of time licking their fur. This consumption of the oil can actually lead to kidney failure in the long term. Global warming and the melting of arctic ice is also a problem for these creatures. As there is less ice, they are required to swim and travel farther to find food. The more they have to swim, the more of their fat stores and energy reserves they use, making survival without food even tougher. When a female is under enough stress from lack of food, she will refuse to mate, thus threatening the species even further. If they do mate, many of the young will not survive do to the lack of food for both mom and cubs. The final predator that polar bears face is humans. It is illegal to hunt them, but unfortunately this doesnt stop everyone. Often the hunting is for no other purpose than the thrill of the hunt (sport). As of 2008 there was believed to be around 25,000 of these amazing creatures left in the wild. By the year 2050, it is estimated that without change in conservation, only about 2/3 of the current population may remain. (Polar Bear Conservation).
These creatures are amazing animals. Everything about them causes me to look for a creator who designed them perfectly. For this research project I had the opportunity to visit polar bears in two different zoos. In January, I went to the San Diego Zoo with my daughter and two granddaughters while on vacation. In February I went to Point Defiance Zoo and Aquarium near my home with another daughter and two grandchildren. Ive included some photos from both zoos and a video conversation with a zoo staff member at the San Diego Zoo at the polar bear exhibit. I have always been fascinated by these giant bears and studying them has only increased my fascination. Its enlightening to me that even at the top of their food chain, these animals are still threatened, mostly due to man. It reminds me of the relationship God commanded us to have with His creation and that not only are we to have dominion over it, but we are to care for it the best way we can. As we learn more about these animals and their environment, we are more equipped to protect them and fulfill our role in relationship with Gods creation.
References”Anatomy and Physiology.” Polar Bear Experience. Accessed March 11, 2019.
“Behavior.” What Is Climate Change – Polar Bears International. Accessed March 12, 2019.
Britannica, The Editors of Encyclopaedia. “Polar Bear.” Encyclop?dia Britannica. February 22, 2019. Accessed March 11, 2019.
Burnie, David. The Kingfisher Illustrated Animal Encyclopedia. New York: Kingfisher, 2000.
Lynch, Wayne. Planet Arctic: Life at the Top of the World. Buffalo, NY: Firefly Books, 2010.
“Polar Bear Conservation.” Animal Facts and Information. Accessed March 12, 2019.
“Polar Bear Reproduction.” Polar Bear Facts and Information. Accessed March 12, 2019.
“Polar Bear Scientific Name | Scientific Classification PolarBearFacts.net.” PolarBearFacts.net. February 06, 2018. Accessed March 11, 2019.
“Polar Bear.” WWF. Accessed March 11, 2019.
“The School: Polar Bear Adaptations for Hunting.” One World One Ocean | The Ocean’s Storyteller. Accessed March 12, 2019.