Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"

Something unusual today! We now go very far from the hot savannahs of Africa, to the icy cold of the north. Here you have a Polar Bear, Ursus maritimus. This is one of the most northernly-living of all land mammals, in fact venturing out on the drift ice and often swimming in the sea to the degree that it can be considered a marine species. Its scientific name indeed means 'Maritime Bear'. It is also called a White Bear, in Inuit a Nanook, and Ysbeer in Afrikaans, which means 'Ice Bear'. (There are actually polar bears in South African zoos, and I've seen them, and wondered at them not feeling much too hot.) It was sometimes classified in its own genus, Thalarctos, but recent studies have shown it to be very close to the Brown Bear, Ursus arctos, indeed sometimes hybridizing with it, and thus not warranting the separation. Genetic studies suggest that it separated from the brown bear about 400 000 years ago. Its many unusual features came about over a rather short period of adapting to its extreme environment and lifestyle.

Hyper-predator of the Icy Wastes

Here in sunny South Africa I can't for the life of me imagine why any living thing would want to live in the freezing Arctic, but many things do, and apparently thrive! So it is with polar bears. Almost every feature of theirs is some adaptation against the cold.

Although polar bears are associated with drifting sea ice, they also venture far on solid land and are found as far south as Newfoundland and James Bay in Canada. They still retain the versatility of the basic bear form and are able to walk, run or swim long distances. They do most of their hunting on and around the sea ice over the continental shelves of America and Eurasia, not so much over the deep Artic sea. These parts of the Arctic sea are particularly productive, and the favoured prey of polar bears are seals of various species.

The first notable adaptation of the polar bear is its size. It is the largest of the living bears, with males averaging 350-700 kg/770-1540 lbs. Females average less than half the size of males, 150-250kg/330-550 lbs. The largest polar bear so far recorded was a reputed 1 000 kg/2200 lbs in weight. This one, mounted, stands 13.4 m/11'1" tall on its hind legs; on four legs, a polar bear can be 1.6 m/5'3" tall at the shoulder. Large body size helps any animal conserve body heat in a cold environment. The bears have streamlined shape with long neck and body, making them good swimmers. Their ears are very small, and they have hardly any tails, so that they don't lose heat through those surfaces. They have very broad paws, up to 30 cm/12" in width, with rough under surfaces and relatively short, curved claws. This is to get good traction on ice and to dig in snow, as well as helping them swim better, doggy-paddle style. One has been recorded swimming 700 km/440 miles non-stop over nine days! They can also swim underwater, holding their breath for three minutes. And on land they can run at 40 km/h, that's 25 mph.

Its white fur is also an adaptation. Not only does this camouflage them against the snow and ice, making them a tad harder for their prey to spot, but it also insulates them against the cold. The outer or guard hairs reach a length of 15 cm/6". They're not actually white, but transparent, lacking the dark pigments or melanins present in the fur of other bears. They are hollow, with a column of air inside, which is what gives them the white appearance, and the air also improves their insulating capacity. With age, the fur turns yellowish, or in captivity sometimes greenish due to the growth of algae in an environment that's warmer and more humid than their natural habitat. Male polar bears have long fringes of hairs on their forelegs, which appear to make them more attractive to females, similar to the mane of a male lion.

Beneath its coat and skin a polar bear carries a layer of fat about 10 cm/4" thick. This is not only an energy store, but also additional insulation against the cold.

Polar bears are the only members of the bear family that are hyper-carnivores, that is to say with a predominantly meat-based diet, and minimal plant food. This is because plant growth is very sparse or absent in the Arctic. Yet, polar bears will eat some plant food such as berries, roots, seaweed and grass, to tide them over until they can find meat again. While preferring seals, the also hunt many other animals from musk oxen and reindeer to lemmings, birds, crabs and fishes. On land, a polar bear hunts by stalking, crouching down behind rocks and bushes to creep up as closely to its intended victim as possible before rushing out to catch it.

But polar bears prefer sea mammals for their food, because they need the very rich fat present in these animals, without which they will waste away. Sometimes they get this even on land, with a whale or dolphin carcass that washed up on a beach. But most of the times they need to go hunting on the sea ice.

The way polar bears hunt takes advantage of the need for seals, and even dolphins and whales, to come up and take a breath at the water's surface every now and then. A bear will wait next to an open area in the sea ice; it chooses the place by its keen sense of smell, being able to scent a place where a seal regularly emerges. (It is often said that a bear lying in wait beside a breathing hole will cover its black nose with its paw so that the seal won't see it, but this appears to be a myth.) As soon as the seal comes up to breathe, the polar bear grabs it with a huge paw, hauls it out and kills it with a bite to the skull. Young bears will eat the whole seal, but older bears will just eat the skin and blubber layer. The leftover carcass might then be scavenged by some younger bears. Otherwise, the leftovers are scavenged by other Arctic predators like gulls and polar foxes. After feeding, polar bears will wash the blood off their fur, which otherwise would make them very conspicuous, using sea water or snow.

Aside from capturing seals like this, polar bears will also sneak up on seals that are lying and resting on the ice, or mother and baby seals in their dens which they dig in the snow. They have been recorded attacking and killing even adult bull walruses, which can be double their weight or more, that come out on shore to rest.

For polar bears, the summer to fall is the time of food shortage. With the sea ice disappearing or dwindling, they're often stuck on dry land. Their fat layer helps them to survive a long time without food, and in the (relative) warmth of the summer the fat is less necessary for insulation. But bears don't like to starve, and sometimes raid the garbage dumps of humans, which can be dangerous for them as well as for the people.

Making Baby Bears

Being very large mammals, polar bears live long and reproduce fairly slowly. They're not the most monogamous of mammals: males mate with several females, and females often with more than one male. They get together on the sea ice in spring, the males fighting each other for the privilege of mating with a female. The mating happens over the course of about a week, and stimulates the female to ovulate. The sperm fertilizes the egg, but then the egg goes into suspended animation, not developing any further for about four months, giving the female time to eat and fatten up, sometimes gaining as much as 200 kg/440 lbs of bodyweight! This will help her nourish her pups with her milk, which as you might expect is very rich in fat.

When she's ready to give birth, the female will dig a den for her and her pup or pups. This is usually in snow on land, but rarely on sea ice or alternatively in frozen soil on land. The den is deep and the entrance usually closes up with snow while the female remains inside. The snow acts as excellent insulation, keeping the interior climate mild. She doesn't go into torpor as such but into a very relaxed and immobile state. The pups, typically two per female, are born in summer. They only weigh 900g/2 lbs at birth, and are blind and covered in thin, downy fur. She keeps them close to her body to warm them. Without emerging to feed, she remains in the den until early spring, slowly using up the fat she gained earlier as she suckles her young. When she breaks out, her cubs weigh about 10-15 kg/22-33 lbs. She now teaches them to hunt. They stay with her for quite some time, up to two and a half years, before she chases them off to live on their own. Sometimes a female will adopt the cub of another female, but also, sometimes males or females will kill and even eat other bears' cubs. Cannibalism in polar bears may work against them by transmitting to them a parasitic roundworm.

Living slowly, polar bear females become sexually mature at around four years, males at six, although they might not breed until they're ten. In the wild, polar bears can reach the age of thirty, while in captivity the oldest one recorded was 43.

Are Polar Bears in Trouble?

On the one hand, it seems as if polar bears have a safe gig. They live in regions only very sparsely inhabited by humans; they've been hunted for ages by the local Inuits and other Arctic peoples without that seeming to have affected their numbers much. With modern firearms, hunters began taking a larger toll on them and hunting restrictions are now imposed in all countries where they occur, including a complete ban in Norway. Their numbers recovered somewhat as a result of this. Presently however they face a new potential threat, climate change.

Climate change is, as you may know, a very controversial topic; there are people considering it a great global catastrophe while others downplay its importance or even deny it outright. But there are data indicating that a steady climb in global average temperatures is indeed happening all over the world, and perhaps more in the Arctic than elsewhere. While it might look slow and small to us, even just a small change in the temperature can have big repercussions. Water ice has a fixed, exact freezing temperature; warm it up even just a fraction of a degree, and it melts. Polar bears are extremely dependent on the sea ice; without lots of ice floes to walk on and from which to hunt, they can't get as much food as they need. They need to walk and swim greater distances to their hunting grounds. Females about to have cubs are especially vulnerable; the ice melting too soon means she can't put on enough fat to nourish herself and her cubs during her time in the den. Warmer temperatures also mean a greater risk of the snow or mud of the den melting and thawing and collapsing on her and her cubs. Warmer climates even mean that diseases and parasites may flourish and infect more bears.

With less sea ice to hunt, bears may choose to venture inland to see what food they can find there, and this might bring them in contact and conflict with humans. And in such conflict, the bears are typically the losers.

The effect of global warming on polar bears is greatest in the south of their range, which is the warmest part, and where a small increase is thus most likely to lead to a lot of ice melting. Around Hudson Bay in Canada, ice floes now start to break up three weeks earlier than they did thirty years ago, and bears over that time have become lighter in body weight. This should be a clear indicator that something bad is happening. Some scientists have predicted that by 2050, as a result of climate change, the population of polar bears might be reduced by two thirds. On the other hand, the bears may prove adaptable and able to learn how to live more efficiently with resources they can find on dry land. But also, it may be that on land they will find themselves outcompeted by the brown bears already there. We just don't know for sure.

But apart from this controversial impact on their environment, there's the more clearly visible and provable forms of pollution that polar bears also suffer from. Humans now produce so much polluting substances that many of these end up in the oceans in fishes and seals and other things, and these chemicals become concentrated in the tissues of polar bears, sometimes poisoning them. They also suffer from oil spills: their fur, coated in oil, loses its insulating properties, and if they lick the oil off, ingesting it, it might damage their kidneys.

While one of the top predators in the high Arctic, polar bears are themselves also preyed upon by a few species (other than humans), mainly when they are swimming in the ocean, such as killer whales and sharks. They are a keystone species in their food webs and are thus very valuable as indicators of overall ecologic health; as such, any decrease in their numbers is a cause for alarm. It's rather difficult to actually determine just how badly at risk they are. Recently, populations have seemed to be stable, but we're not sure about how large the population was in the pristine past; they've been naturally recovering from over-hunting over the past several decades. It's even difficult to tell just how many they are, since the Arctic is vast and the bears difficult to locate. We're estimating right now that there are between 20 000 and 30 000 of them. Whatever the case, we'd better be watching them carefully.

Willem

21.12.20 Front Page

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