COMPETITION - Sexual Dimorphism
When looking at male and female polar bears, one can see that they are much different in size. This is a case of sexual dimorphism, which is a common feature in species where males compete for females.
Males can be up to three times as big as females (Derocher et al., 2010), which comes in handy when males must fight each other for the right to mate with a breeding female. During breeding season, one female bear may be courted by multiple males, who will then fiercely fight each other until one successfully chases the rest away. These fights often aren't deadly, but males tend to have injuries and scars that accumulate throughout their life (Seaworld).
When looking at male and female polar bears, one can see that they are much different in size. This is a case of sexual dimorphism, which is a common feature in species where males compete for females.
Males can be up to three times as big as females (Derocher et al., 2010), which comes in handy when males must fight each other for the right to mate with a breeding female. During breeding season, one female bear may be courted by multiple males, who will then fiercely fight each other until one successfully chases the rest away. These fights often aren't deadly, but males tend to have injuries and scars that accumulate throughout their life (Seaworld).
![Picture](/uploads/1/3/6/4/136491154/editor/polar-bear-den.jpeg?1620091520)
BREEDING
Breeding season for polar bears typically occurs in the spring time between late March and early May, although there is evidence that they mate as late as June and July (Smith and Aars). As is common in bear species, actual pregnancy, or 'implantation,' doesn't occur until later in autumn.
In a process called delayed implantation, or diapause, the embryos formed after mating become metabolically dormant, and will not be implanted into the uterus until conditions are optimal for gestation and birth (Cha et al.). This delay allows mothers to find an environment that is just right, which increases the chances of survival for both offspring and parent.
Denning
- Before birth, pregnant females will dig a deep den somewhere in the habitat before beginning gestation. The location of this den is an important decision, as this den is the shelter that the mother and her cub will live in until next spring - almost half a year!
As mentioned, gestation and birth occur in the fall. Gestation occurs over 60 days, after which a litter of typically two cubs is produced (National Wildlife Federation). Although two cubs is expected, a litter can also have three, four cubs or even just one.
After birth, the mother enters a fasting period while also providing milk for her cubs. Newborn cubs are usually only 12-14 inches long, and weigh about one pound (Polar Bears International), yet grow quickly and require constant sustenance. To be able to provide for her offspring throughout the denning period, it's important that the female eats enough before gestation so that she has adequate fat and energy reserves. This largely explains why polar bears love to eat seals, because the animals are rich in fat and provide the blubber needed by polar bears for these long periods of denning.
Once spring arrives, the mother and her cubs finally leave their shelter. Over the next 2-3 years, the cubs begin to learn about the world and the skills required to survive, while the mother provides protection, hunts for herself and her children, and teaches her offspring how to live in their habitat. After this time, the cubs are fully grown, sexually mature and become independent of their mother.