How Do Female Polar Bears Prepare to Reproduce?

In late autumn, a female polar bear will begin to dig a winter cave. If she mated in the early spring, she will have spent the entire summer eating in earnest, as she'll need to gain at least 400 pounds (181 kg) for a successful pregnancy. The den will protect her from the harsh Arctic wind and provide a safe place to sleep. In early winter, every three years or so, she’ll give birth there, usually to one or two cubs, and they’re amazingly small. A polar bear cub weighs about a pound (454 g) at birth, and is usually about one foot (30.5 cm) long.

Go, cubs, go:

• Polar bear cubs are born blind, toothless, and with only a very thin layer of fur. They usually open their eyes within the first month, and begin walking around the den a month after that.
• Cubs grow quickly, subsisting on a diet of their mother’s fat-rich milk. They begin eating solid food when their mother makes her first kill on the sea ice. Seal is the meal of choice.
• When her cubs are about 30 months old, the female polar bear is ready to breed again. She’ll shoo the cubs away, sending them off to start lives of their own.

Frequently Asked Questions

How do female polar bears find a suitable denning location for reproduction?

Female polar bears seek out areas with deep snowdrifts for denning, often on coastal banks or hillsides. They use their powerful paws to dig dens that provide insulation and protection from the elements. The chosen site is crucial for the survival of her cubs, as it must remain undisturbed and at a stable temperature throughout the denning period.

What is the significance of the female polar bear's weight before entering the den?

Before denning, female polar bears must accumulate substantial fat reserves, as they can fast for up to eight months during denning and nursing without eating or drinking. According to Polar Bears International, a pregnant female typically needs to weigh at least 500 pounds to ensure she has enough energy to sustain herself and her cubs until the spring.

How long does the gestation period last for polar bears, and when do they give birth?

The gestation period for polar bears lasts about eight months, including a period of delayed implantation. Actual embryonic development is only about two months. Females give birth during the winter months, usually between November and February, while they are in their dens in a state of reduced metabolic activity.

What adaptations do polar bear cubs have at birth?

Polar bear cubs are born extremely small, weighing just over a pound, blind, and with a light downy fur. Despite their vulnerability, they are well adapted to rapid growth, thanks to the rich milk provided by their mother, which can be up to 31% fat, as reported by the World Wildlife Fund. This allows them to quickly gain weight and insulation.

How do female polar bears care for their cubs after birth?

After birth, the mother's den becomes a nurturing sanctuary where she keeps her cubs warm and feeds them with her fat-rich milk. She remains in the den without food, relying on her fat reserves, and attentively cares for her cubs, stimulating them to breathe and keeping them close to maintain their body temperature until they are ready to venture outside.

When do polar bear cubs leave the den, and how do they survive the harsh conditions?

Polar bear cubs typically leave the den around March or April when they are strong enough to face the Arctic climate. Their mother teaches them vital survival skills, such as hunting and swimming, over the next two years. During this time, the cubs rely on their mother's protection and learn to navigate the challenging environment of the Arctic.