The Polar Bear (Thalarctos maritimus or Ursus maritimus) is a large mammal of the order Carnivora, family Ursidae. It is a circumpolar species found in and around the Arctic Ocean. It is the world's largest land carnivore. Adult males weigh from 400 to 600 kilograms and occasionally exceed 800 kilograms. Females are about half the size of males and normally weigh 200 to 300 kilograms. Adult males measure 240 to 260 centimeters and females 190 to 210 centimeters. At birth, cubs weigh 600 to 700 grams.
The Polar Bear is instantly recognisable by its white coat. Unlike other arctic mammals it never sheds this coat for a darker colour in summer. The hair is not actually pigmented white; it is unpigmented and hollow, like white hair in humans.
An interesting feature of the coat is that it appears black when photographed with ultraviolet light. A number of people have suggested that this is because the hairs channel the light to the black skin of the bear to help it stay warm during the cold, sunless winters. Measurements show, however, that the hairs strongly absorb violet and ultraviolet rays. This is why Polar Bear's pelt often appears yellow. More colourful Polar Bear have occasionally been reported. In February 2004, two Polar Bears in a Signapore zoo appeared to turn green as a result of algae growing in their hollow hair tubes. A zoo spokesman said that the algae had formed as a result of Singapore's hot and humid conditions. The bears were washed in a peroxide blonde solution to restore their expected colour. A similar algae grew in the hair of three Polar Bears at San Diego Zoo in the summer of 1979. They were cured by washing the algae away in a salt solution.
Polar bears are wonderfully insulated; to the point where they overheat at temperatures above 50°F (10°C). Their insulation is so effective that when viewed with infrared (heat) camera they are barely visible. Only the pads of their feet emit detectable heat.
It is the most completely carnivorous member of the bear family and feeds mainly on seals. Polar Bears are superb swimmers and can often be seen in open waters miles from land. This may be a sign that they have begun aquatic adaptations to better catch their prey. They also hunt very efficiently on land due to their prodigious speed; they are more than capable of outrunning a man. As a pure carnivore predating upon fish-eating carnivores, the Polar Bear ingests large amounts of vitamin A, which ends up stored in its liver: in the past, arctic explorers have been poisoned by eating Polar Bear liver.
Polar Bears are currently threatened, not mainly by hunting, but by habitat loss caused by global warming; for example, the area of ice covering Hudson Bay in Northern Canada in winter is shrinking, limiting their access to seal prey. The sensitivity of the survival rates of the bears to global temperature is attested to by the population bulge in the cohort of bears born during the transient cooling that followed the eruption of Mount Pinatubo in 1991.
A Polar Bear is depicted on Canada's $2 toonie coin.
Penguins (order Sphenisciformes, family Spheniscidae) are an order of flightless birds living in the southern hemisphere. They are not, contrary to popular belief, only found in cold climates, such as Antarctica. Many species live as far north as the Galapagos Islands and will occasionally cross the equator while feeding.
Penguins like to stay and move within large groups. Most penguins live off krill, fish, squid, and other forms of sealife that they catch while swimming underwater. They spend half of their life time on land and half in the oceans.
The largest species is the Emperor Penguin: adults average about 1.1 meter tall and mass 30 or more kilograms. The smallest penguin species is the Little Blue Penguin (also known as the Fairy Penguin), which is typically 35 to 40 cm tall and 1 kilogram. Generally larger penguins retain heat better and thus inhabit colder regions, while smaller penguins are found in temperate or even tropical climates.
Penguins emerged in the Eocene era 40 million years ago. Birds like Palaeeudyptes from the Eocene, Pachydyptes from the Miocene and the now extinct Great Auks resembled modern penguins. The links between other bird orders and penguins are still unknown. A distant relationship between penguins and petrels is assumed, but not proved. Most fossil penguins known were large, but not larger than the modern Emperor Penguin. All lived in the southern hemisphere.
Penguins are superbly adapted to an aquatic life. Their wings have become flippers, useless for flight in the air; in the water, however, penguins are astonishingly agile. Within the smooth plumage a layer of air is preserved, ensuring buoyancy. This is the reason a chain of air bubbles stretches behind a diving penguin. The air layer also helps insulate the bird in the icy waters of the Antarctic. The plumage of penguins in tropical and temperate zones is much thinner.
On land, they use their tails and wings to maintain balance.
All penguins have a white underside and a dark (mostly black) upperside. This is for camouflage. A predator looking up from below (such as a Killer Whale or a Leopard Seal) has difficulty distinguishing between a white penguin belly and the reflective water surface.
Diving penguins reach 6 to 12 km/h, though there are reports of velocities of 27 km/h (which are probably realistic in the case of precipitate flight). The small penguins do not usually dive deep, their prey is caught near the surface, and most dives are only one or two minutes in duration. They can dive deep in case of need, however: the large Emperor Penguin has been recorded reaching a depth of 267 metres and staying down for 18 minutes.
On land, penguins are clumsy. They either waddle on their feet or slide on their belly across the snow. However, they can actually run as fast or faster than most humans. They slide on their stomachs, called "tobogganing", to conserve energy and move relatively fast at the same time.
Penguins have an excellent sense of hearing. Their eyes are adapted for underwater vision, and are their primary means of locating prey and avoiding predators; in air, conversely, they are nearsighted. Their sense of smell has not been researched so far.