Between April and late June, as the snow starts to melt and days become longer, adult male polar bears begin to find mates on the sea ice by following scented trails left by footpads.
Males reach sexual maturity between ages six and ten, and females between ages four and six.
Mating takes place on the sea ice but the fertile eggs do not implant until the following fall, and only if the mother has enough fat to sustain herself and her cubs during long the denning season. This process is called delayed implantation. Adult males stay with the female for a few days before taking off on their own.
Denning (Fall & Winter)
After feeding throughout the summer and fall, a pregnant female polar bear starts to build a maternity den, where she will give birth to her cubs and nurse them until spring.
Pregnant polar bears will choose a den site in snowdrifts along coastal and river bluffs, in hills near sea ice, or in banks of snow on the frozen sea. Along Southern and Western Hudson Bay, mother bears will dig into raised peat soil found in palsa formations or along lakeshores and rivers.
To build her den, the female excavates a small snow cave—just large enough for her to turn around in. She then waits for the snow to close the entrance tunnel.
Wild polar bear cubs are most often born in December. The mother bear gives birth to one, two, or three cubs. Twins are most common.
The family remains in the den until March or early April. During her entire time in the den—four to eight months—the mother doesn't eat or drink. Her sole purpose is to provide for her cubs.
Newborns are 30-35 centimeters long (12 to 14 inches) and weigh little more than half a kilogram (one pound). They are blind, toothless, and covered with short, soft fur. They are completely dependent on their mother for warmth and food. They grow rapidly on their mother's rich milk (31% fat), and continue nursing for at least 20 months.
Emerging from the Den (Spring)
Polar bear families generally emerge from their dens in March or April when cubs are strong enough to survive outside and ready to make the trek to sea ice.
Now, mother bears can start teaching their young how to survive in the Arctic.
Today, cubs generally stay with their mother for 2 1/2 to three years, learning how to hunt, feed, swim, and survive.
Between the time they leave their mother and they are mature enough to mate, polar bears are called subadults.
Historically, polar bears in Hudson Bay weaned in half the current time, due in part to high productivity in that region. This is becoming less frequent as that ecosystem changes.
Watch polar bears as they travel across the sea ice to hunt seals.
Polar Bear FAQ
We answer the most frequently asked polar bear questions.