The World of Polar Bears

Behavior

A. Daily activity cycle

1. Polar bears are most active the first third of the day and least active the final third of the day.
2. In the Canadian Arctic, adult female polar bears with cubs hunt about 19% of their time during the spring and about 38% of their time during the summer. Adult male polar bears hunt about 25% of their time during the spring and about 40% of their time during the summer (Stirling, 1978).
3. When not hunting, polar bears are often sleeping or resting.
   a. On warm days polar bears sprawl out on the ground or ice, sometimes on their backs with their feet in the air. They may also make temporary snow or earthen pits to lie in.
   b. On cold days polar bears curl up and often cover their muzzle area. During the winter, some polar bears excavate temporary dens or find natural shelters to stay warm. They may use these shelters for several months at a time.

B. Walking and running

1. Like humans, polar bears walk on the soles of their feet with their heels touching the ground first. Like other bears, they can also stand on their hind feet and walk upright for short distances.
2. Polar bears generally walk with a steady, lumbering gait. The front paws swing outward with each step, landing slightly pigeon-toed. The head swings gently from side to side. The walk has a four-beat pattern, first the right front foot touches the ground, then the left hind foot, then the left front foot, and lastly, the right hind foot.
3. The bulky build and swinging gait cause polar bears to use more than twice as much energy to move at a given speed than most other mammals (Stirling, 1988).
4. The average walking speed of a polar bear is 5.5 kph (3.4 mph) (Stirling, 1988).
5. When being chased or charging prey, polar bears can run as fast as 40 kph (25 mph) for short distances (Domico, 1988).

C. Social structure

1. Polar bears are basically solitary. Usually, only two social units exist: (1) adult females with cubs and (2) breeding pairs.
2. Polar bear aggregations.
   a. Polar bears will aggregate to feed on large whale carcasses and at dump sites.
   b. In some southern regions, like Hudson Bay, bears aggregate on land during the ice-free summer and autumn months.
3. On occasion, adult and sub adult (ages 30 months to five or six years) polar bear males will feed and travel together for short periods of time.

D. Social behaviour

1. The most constant social interaction occurs between mother and cubs. Polar bear mothers are attentive, frequently touching and grooming their cubs.
2. Polar bear breeding pairs remain together for one week or more, mating several times.
3. Aggression occurs between males during the breeding season and when males attempt to steal food caught by other polar bears.
4. Play fighting has been observed between aggregating sub adult and adult male polar bears.
5. Young polar bear cubs chase and tackle their siblings.

E. Hibernation

1. Hibernating means to pass the winter in a dormant or lethargic state. Animals that hibernate store body fat when food is plentiful. When food is scarce, they hibernate, living off their stored body fat.
2. Polar bears don’t enter deep hibernation. Deep hibernation applies to an animal whose body temperature drops to 5C (41F) for a period of days or weeks. Deep hibernators also show a marked drop in heart rate, and are slow to wake up when disturbed.
3. Only pregnant female polar bears hibernate.
   a. Polar bears aren’t deep hibernators, but enter a state of carnivore lethargy. Though hibernating females sleep soundly, they’re easily and quickly aroused.
   b. The female polar bear’s heart rate slows to about 27 beats per minute from a normal resting heart rate of about 46 beats per minute (Stirling, 1988).
   c. When hibernating, a female’s body temperature may drop slightly, perhaps to 35C (95F), or it may remain normal at 37C (98.6F). Unlike most other hibernators, female polar bears give birth while hibernating. High body temperature is needed to meet the demands of pregnancy, birth, and nursing (Stirling, 1988).
4. Researchers have found that nonhibernating polar bears, during times of food scarcity, can efficiently utilize their energy reserves much like hibernating bears (Stirling, 1988).

F. Tracking

1. Scientists use radio collars to track the movements of polar bears.
   a. Once a polar bear is fitted with a radio collar, the collar sends signals to a receiving station via satellite. Scientists can enter the data into a computer program that plots the polar bear’s path.
   b. Only female polar bears can be tracked using radio collars. Male polar bears have necks wider than their heads, and the collars simply fall off.
2. The movements of polar bears can also be studied by following their tracks in the snow, usually by aircraft.
3. Other behaviours are recorded by observing polar bears directly, or finding evidence of polar bears, such as a partially eaten seal.
4. Most polar bear research is conducted in the spring or summer when weather conditions are more favourable to humans.

G. Attacks on humans

1. Humans may encounter polar bears wherever human and polar bear habitats overlap. Polar bear attacks occur most often at sites of human habitation, such as hunting camps, weather stations, and towns. Compared to other bears, polar bears are more willing to consider humans as prey. Consequently, the person attacked is usually killed unless the polar bear is killed first.
2. Polar bear subadults and females with cubs attack most often. They’re also the chief scavengers (among polar bears) of human dump sites. Both groups tend to be thinner and hungrier; subadults are inexperienced hunters, and females with cubs must feed themselves and their young.