Ursus maritimus

Family : Ursidae

Text © DrSc Giuliano Russini – Biologist Zoologist

 

English translation by Mario Beltramini

 

The Polar or White bear (Ursus maritimus Phipps, 1774), which till the eighties was inserted by the taxonomical biologists in the genus Thalarctos with the species Thalarctos maritimus , is a quadrupedal, eutherian, placental mammal, in the specific, the largest terrestrial carnivore of the planet (along with other species of bear, afferent to the superclass of the Ganthostomes (Gnathostoma), class Mammals (Mammalia), subclass Placentals (Placentalia), order Carnivores (Carnivora), suborder Fissipeds (Fissipedia), family Ursids (Ursidae), subfamily Ursines (Ursinae), Ursus.

The bears, large carnivorous plantigrades (so called because, during the deambulation, they stand on the entire sole of the foot, contrary to the digitigrade animals, such as the felines, which rest on the tip of the toes), are diffused mainly in the cold and temperate regions of the Boreal, or Northern Hemisphere; they form one of the most homogenous and better organized families of the order they belong to.

Presently, the biologists describe seven genera to which is dated back a number of species upon which there is not an unanimous agreement, even inside the International Commission for Zoological Nomenclature (ICZN). The general anatomic characteristics of the ursids, which form the general tendencies, agree on the fact that all species are easily recognizable for an always massive structure, joined by stout and rather solid forms.

The back is always humpbacked in correspondence with the shoulders, the neck is short and ample, and the head, which is quite massive, ends in a muzzle with a straight profile and with a shape getting progressively to that of truncated cone. The eyes are rather small and the same can be said for the roundish ears. The legs are stocky and strong and end with a very wide sole of the feet, which is used for the deambulation, whence the definition of plantigrades. The feet are equipped with robust, non retractile, big nails. The tail is always reduced to a short stump; the fur is always very thick and abundant, even if some species do have a shorter hair.

Compared to the other carnivores, the bears have a dentition which is more suitable for chopping the vegetable foods, even if this is not the case, as we shall see, of the polar bear, therefore the back molar is greatly developed in almost all species, whilst in the other families of the order, such as in the Felids (Felidae) and the Canids(Canidae) it is reduced or completely missing. Most of the species of ursids have twelve incisors (six upper and six lower), these are ascribed in the family of the Ursids (Ursidae) and in the subfamily of the Ursines (Ursinae), whilst for the Labiated bear (Melursus ursinus), which has only four incisors in the upper jaw the biologists have created the subfamily of the (Melursinae). Historically and ethno-zoologically, the relationship between the various species of bear, especially the largest and ferocious ones and the Man (Homo sapiens), has always had a conflictual nature. Since the prehistoric times, for in stance, the primitive man was struggling against the Cave bear (Ursus spelaeus, living in Eurasia in the Pleistocene), nowadays extinct and of gigantic proportions. Obviously, seen its mass and its ferocity, the human being was a prey, at least till when this last one became able to make offense instruments which allowed him, by means of forms of hunting organized in group, of not standing always on the succumbing side.

Over the centuries, in the most urbanized areas, the bear often ravaged the herds and the flocks of the breeders. It was therefore hunted, also for eating its meat and utilizing the fat and the fur; the meat of all species of bear is, in fact, comestible, and sought for by the man. We do not talk only of the tribal populations, such as the Eskimos, who hunt the polar bear for utilizing its fur in addition to the fur and the meat, necessary to their survival, but also of the so-called civilized man, for selling its meat under form of gigantic steaks in the restaurants, as it happens still now in many cities of several Canadian and Siberian provinces, to the extent that now do exist some bear farms, where some species, less aggressive, are bred for such purpose.

Furthermore, due to the destruction during the time, done by the human being, of the eco-systems and of the biotopes where the various species of bear live, as well as due to the increasing pollution, these animals are more and more endangered in various geographic areas.

In the case of the Polar bear (Ursus maritimus), the melting of the Arctic polar ices adds up to the other aforementioned phenomena of environmental degradation. The International Union for Control of Nature (IUCN) has established nowadays a status of vulnerability for this species.

The hunting to which they have been subjected, especially for sporting, shooting from a flying chopper, allowed till the half of the eighties of the last century, has given a substantial contribution to their decrement.

Today, such a stupid venatorial activity is luckily forbidden by a worldwide decree. The polar bear is now a severely protected species, especially by the Russians. Only the killing of a few heads per year is allowed to the Eskimo tribes for their survival. Their lairs for the winter are numerous, close to the human settlement in the Wrangel Island, and island of the Arctic Ocean, between the Chukchi Sea and the East Siberian Sea.

The environmental pollution, caused, especially in the past (till all the eighties of the last century), of motor vehicle fuels with discharges containing lead, or, still now, the utilization in agriculture of some chemically stable insecticides, such as the DDT, which irreversibly fix in the living organisms, entering the food chain, have shown and still show all their pernicious effects also in the isolated lands of the Arctic Polar Circle and of the North Pole. As a matter of fact, they have measured traces of their atmospheric presence, into the ice and the fat of the polar bears, areas where, obviously, the city traffic and the agricultural activity are absent.

Zoogeography

The Polar bear (Ursus maritimus) populates the Arctic coasts of the Boreal Hemisphere, venturing only slightly and only in some regions south of the Polar Arctic Circle.

It is diffused along all the coasts of Greenland, of New Zemlya (or Novaya Zemlya, a Russian archipelago formed by two major islands separated by the Matochkin Strait), of Spitsbergen (a Norwegian island, the largest of the Svalbard archipelago) and the great Arctic Canadian islands (Baffin, Victoria, Ellesmere, Banks, etc.); on the mainland, then, they are present on the northern coasts of Siberia, Canada and Alaska. In Europe, it is encountered in northern Norway, Kanin peninsula in Russia and in part of Island; occasionally, it can move, for hunger, even more to the south.

Beyond the Arctic Sea, these large bears may be found in the Kuril Islands (a 60 islands archipelago placed between the north-eastern part of the Japanese island of Hokkaido and the Russian peninsula of Kamchatka), in Sakhalin (a Russian island of northern Pacific off the eastern coasts of Russia), in Kamchatka (a peninsula off the extreme eastern extensions of the Russian territory, just over the archipelago of the Japanese islands), in Newfoundland and in Nova Scotia (respectively, an island and a federal province of Canada).

Ecology-Habitat

Actually, the polar bear, more than being an inhabitant of the coasts of the islands, can be considered as an animal spending part of its time at sea and part on the borders of the Pack ice (a layer of sea ice, produced by the disintegration of the ice shelf). It is an excellent swimmer, fast and agile in the immersions; furthermore, it is capable to run with remarkable speed on the ice and the snow. Whilst most of the bears are omnivorous (nourishing of flesh of vertebrates such as fishes, mammals, as well as of insects, berries, fungi and honey), the Ursus maritimus is an exclusively carnivorous species, even if, when the preys are scarce, it nourishes also of berries, lichens, and of other rare vegetal forms of those zones, such as the Polar poppy and the moss campion and of the vegetables of the Arctic tundra. Nowadays, unfortunately, especially in winter, finding less and less food, it frequently moves southwards; for instance, in Alaska, it is sighted always more frequently while looking for something to eat among the garbage of the small urban centres. In the specific, it nourishes of seals (see text Pinnipedia) and young of walruses, cetaceans (such as those of beluga and of narwhal) and of fishes.

The polar bear forms the last ring of a food chain starting with the plankton and reaching the bear, through the fishes and the seals. The concentration of vitamin A increases along the food chain and the vertebrates accumulate its surplus in the liver. The concentration in the liver of the polar bear is so high that it is toxic for the man as well as for many animals. The polar biologist K. Rodhal has found 26.700 International Units (UI) of vitamin A per gram of liver of a polar bear killed in Greenland; and some rats passed away as they had eaten 0,5-07g of this liver per day for about one week. The fiery character, the polar bear does not hesitate aggressing the human being and killing him, even if not disturbed or hunted. But, thanks to its particular area of distribution, living in area practically uninhabited, it has never caused human or domestic animals massacres. Substantially, excepting the human being, it does not have predators and therefore it can be defined as an Apex predator.

Morpho-physiology

This species differs from all other mainly due to its way of life and to its morphological characteristics. As a matter of fact, the Ursus maritimus along with the Kodiak or Alaska bear (Ursus middlendorffi), is the species reaching the largest size of the family.

The males have a total length close to the three metres, with a weight not much under the ton; the females do not exceed the 2,10 m of length per about 300-400 kg of weight, obviously, before delivering and nursing.

The polar bear, in respect to the Brown bear (Ursus arctos), has a slenderer silhouette, with the head proportionally smaller and more elongated muzzle. The legs are exceptionally robust, with the sole of the paws very ample and digits united among themselves up to half of their length, by means of a cutaneous membrane apt in helping its swimming in the sea. The fur is very thick and long, due to environmental adaptation, of a uniformly candid white colour tending to the yellowish with the time and in the very old specimens it becomes really yellow. It has a much developed panniculus adiposus.

It lives, as an average, 25-30 years in the wild and can reach even the 40 years in captivity.

Ethology-Reproductive Biology

The males are sexually mature from the fourth year onwards; the females may already procreate by the third year of life. The time of the mating, for the polar bear, is around the end of winter and the beginning of spring.

The periods when the females are available for the couplings are little frequent, as the female does not copulate till when it has young to care and this means every three years; the oestrum lasts a few days and during this period, the male and the female form a pair. The period of pregnancy varies between 195-265 days, in this time the future mother builds up a lair in the snow and eats so much to double its weight. The lair is never too far from the coast in order to facilitate the food research. The polar bear female usually delivers two newborns per pregnancy, these come to life in the winter following the mating and inside the lair where the mother withdraws, without eating, when the delivery approaches.

When just born, the young are blind, naked and weigh about 1-2 kg, but the particular structure of this igloo and the heavy mass of the mother are sufficient to furnish them all the necessary heat. The milk, given for various weeks, is very rich in fats and proteins so much that, when the following spring comes, when they get out from the lair, they have reached about the 20-25 kg of weight.

So, the young come in contact with the outside world when having about 3-4 years of post-natal life, and the mother, very much thinner due the nursing and the fasting, takes them with itself while going out looking for food on the pack for recover the physiological weight.

The separation from the mother takes place only by the third year of life, rather late in the world of the mammals, but during all this time, the mother teaches them the hunting techniques, the dangers of the Pack, the capacity of managing and swimming in open seas and of finding a suitable lair.