The Polish population of brown bears is classified as a nominative subspecies, Ursus arctos arctos L. They are the largest mammalian predator in Poland. Carpathian bears can weigh up to 350 kg (males) and 250 kg (females) and body length can reach more than 2 meters. Bears walk flat-footed and their hindfoot tracks resemble the footprints of human armed with long claws. These animals are only superficially slow and clumsy, and can run at a speed of about 50 km/h. They can jump, swim, climb on the rocks and trees, and their reactions are very fast. They are mainly nocturnal; if undisturbed, bears can become more diurnal. During the day, they usually rest at beds, usually a fresh place dug in the soil within a coniferous ticket.
These large predators do not actively defend their territories. Several individuals can coexist in the same area, especially during periods of food abundance. Adult males are solitary. The home range of adult males usually encompasses those of several adult females, and overlap with those of other males. In the spring, bears rub on the trees and scratch the tree bark to announce their presence and reproductive status. They also remove the bark and eat the phloem of some coniferous species of trees. Telemetry studies conducted in the Bieszczady Mountains revealed that the 9-month home range of an adult male was 1100 km2.
The mating season lasts from May to June. Males may fight over females during the breeding season. Both males and females mate promiscuously and both sexes roam to mate. The implantation of the fertilized egg is delayed; the effective development of the foetus lasts for 2 months. In the winter den, typically every two or three years, the female bear gives birth to 1 to 3 cubs (often twins, but up to 5) in January-February. At the time of birth the size of bear cubs is similar to that of a rat, weighing less than half kg; they are blind and hairless. However, they gain weight quickly by suckling the highly nutritious milk. The female at that time stays with them constantly, and leaves the winter den relatively late. The cubs remain in the den for about 4 months and then accompany the mother for 1.5- 3.5 years. Cubs weaned at 1.5 years of age. Sometimes older cubs from the previous litter accompany their mother after she gives birth to a new litter. A female with cubs may be dangerous, as she can attack in their defence. Sexually selected infanticide occurs in bears, with males killing the cubs which are not their offspring. A female which has lost her cubs, may re-enter the oestrus, which is an opportunity for the male to transfer his genes. Sexual maturity occurs at 5 years at the earliest. Immature bears may have paler fur on collar of neck. Except for females with young, bears are generally solitary, but may gather in large numbers at food resources.
The bear is a generalist species. It is omnivorous, with a highly seasonal diet. In early spring bears feed a lot on winter carcasses of ungulates and artificial food resources - cereals and vegetables used as bait for ungulates. In the Tatra Mountains, in their search of carcasses, bears patrol the avalanche sites, even on very high ridges. They also can be active predators of large animals, such as wild boar, deer and even bison, already weakened by severe conditions of winter. Reports of such cases, however, are not frequent. Later in the spring bears feed on green vegetation (grasses, forbs), young ungulates (actively preyed upon), and insects (mainly ants, wasps and bees). During late summer and autumn, when they store fat for the winter, they forage mainly on berries, tree fruits and beechnuts and hazelnuts. In the Bieszczady Mountains they often forage in the numerous abandoned orchards with cherry, apple and pear trees. One of their preferred delicacy is honey. Tasting this goody apparently makes the bears fall into euphoria.
The beginning and duration of the winter sleep depend much on weather conditions. Most often it starts in late autumn-early winter (in the Tatra Mountains could start earlier, even in October) and lasts till late winter-early spring (end of February-April). Bears sleep in the winter dens, which are secluded and inaccessible places. Winter dens can be located in rock cavities, cavities under fallen trees, hollow trunks of old trees, or they can construct a type of “tent” by placing and bending small trees in young dense coniferous forest. Bears line a comfortable bed inside the den with twigs, moss and grass. Bears’ winter sleep is not a true hibernating status (a state of physiological dormancy, as for example in marmots), and sometimes it can be interrupted during the winter. All the pregnant females sleep during the winter, but males and females which do not expect offspring may be more active in winter time, especially during low frost and high availability of food.