Male polar bears (boars) do not participate in raising their offspring at any point in their lives. This absence of paternal care highlights the species’ solitary nature. The mother (sow) shoulders the entire responsibility of denning, nursing, and teaching the cubs to survive in the harsh Arctic environment.
The Solitary Life of the Male
The male polar bear’s involvement in the reproductive process effectively ends shortly after conception. He is a nomadic hunter, primarily focused on locating seals on the sea ice. This is necessary to maintain his considerable body mass, which can range from 775 to 1,300 pounds in adulthood. His life is generally one of solitude, defined by the extensive distances he roams in search of food and mates.
This solitary lifestyle means the male has no inclination to join a family unit. Adult males pose a serious threat to young cubs through infanticide, the killing of cubs. This behavior is common among male polar bears.
The male perpetrates infanticide to bring the female back into estrus, or breeding condition, more quickly. A female with dependent cubs will not be ready to mate, but the loss of her litter allows her reproductive cycle to reset. This sexually selected behavior provides the male with an earlier opportunity to pass on his genes. Therefore, mothers with cubs must be vigilant, actively avoiding any encounter with adult males.
The Mother’s Extensive Commitment
The mother makes an extraordinary commitment to her offspring, which begins with the denning period. A pregnant female enters a maternity den, typically dug into a snowdrift on land or sea ice, sometime in the autumn. She remains in this den for approximately four to five months. During this time, she survives without eating or drinking, relying entirely on her fat reserves to sustain herself and her litter.
Cubs, usually one or two, are born blind, toothless, and helpless, weighing less than one kilogram, typically in December or January. They grow rapidly on their mother’s rich milk, which contains over 30% fat. The family emerges from the den in late March or April, with the cubs having gained up to 25 times their birth weight.
Once out of the den, the mother teaches her young the necessary skills for survival in the Arctic. She instructs them on how to hunt seals on the sea ice and how to find new den sites. The cubs remain completely dependent on their mother for about 2.5 years, sometimes longer. This prolonged maternal investment means a female polar bear usually reproduces only once every three years.
Reproduction and Mating Season
Adult males and females intentionally interact only during the mating season, which occurs on the sea ice between late March and June. Males locate potential mates by following scent trails left by the females’ footpads. They may engage in battles with other males for access to a receptive female.
Once a male finds a mate, they form a temporary pair bond lasting from a few days up to two weeks, during which multiple mating attempts occur. Following this courtship, the pair separates, and the male returns to his solitary routine.
The female’s reproductive cycle includes delayed implantation, or embryonic diapause. The fertilized egg divides into a blastocyst, but its development is paused for several months. The egg will not implant in the uterine wall until the following autumn, and only if the female has built up sufficient fat reserves. This process ensures that the birth of the cubs is timed to coincide with favorable environmental conditions for their survival.