Polar Bear Lifecycle: From Birth to Death

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Polar Bear Lifecycle: From Birth to Death

Like most other bears, a polar bear has 4 main life stages; birth, cubs, subadults, and adults.

In this article, we’ll look at each of these life stages in detail to understand how their physical characteristics and behavior change throughout their lives.

Polar Bear Lifecycle

1. Birth

The first stage of a polar bear’s lifecycle is birth. Although polar bears don’t hibernate, pregnant females will enter a ‘hibernation-like’ state in a maternity den. Females will enter the den in early Winter and will give birth around 60 days later.

They will enter a low-energy state during which they will not eat, drink, urinate, or defecate, much like a traditional hibernation1 (source: Polar Bears: A Complete Guide to Their Biology and Behavior, A. E. Derocher, 2012).

A female will give birth to between 1-3 cubs. Polar bear cubs are about 30cm (12 inches) long when they are first born and weigh around 454-680g2 (source: The Polar Bear, A. Hemstock, 1999). They have a thin covering of fur and a tiny cry.

However, the mother will remain in the den until they weigh around 10kg and have learned to walk3 (source: Arctic Animals and Their Adaptations to Life on the Edge, A. S. Blix, 2005). The mother will typically spend anywhere from 5-7 months in the maternity den depending upon the region.


2. Cubs

Cubs will emerge from the den around March-April when they will closely follow their mother. She will teach them how to hunt and live in the wild.

Upon first emerging from the den, they will remain in the same area for 1-4 weeks before the mother will lead them across the sea ice and begin learning how to survive 4(source: Polar Bears: A Complete Guide to Their Biology and Behavior, A. E. Derocher, 2012).

Initially, the mother will attempt to lead them across land as they will be vulnerable to hypothermia if they attempt to swim in the sea5 (source: Marine Ecology Progress Series, A.E. Derocher, et al, 2011).

Cubs will stay with their mothers for a total of 2 ½ years before they must live by themselves6 (source: Polar Bears, K. Allen, 2013). This means that the interval between litters for a female polar bear is at least 3 years.

If the mother does not survive, other female polar bears have been known to adopt younger orphan cubs, either claiming them for their own or oftentimes because the cub has started following the mother who assumes it is hers7 (source: Polar Bears: A Complete Guide to Their Biology and Behavior, A. E. Derocher, 2012).


3. Subadults

Once polar bears have left their mothers at around 2½ years of age, they enter the subadult (adolescent) stage of their lifecycle. Subadults who have left their mothers often have difficulty finding food.

At this stage in their lives, they are still growing and have not perfected their hunting techniques. Subadult polar bears also have a low survival rate relative to other bear species.

Although there are few instances of polar bears attacking human settlements and campsites, those that do tend to be malnourished subadult males8 (source: Bears: Their Biology and Management, S. Herrero and S. Fleck, Vol 8, 1989).

Past the age of 4, the survival rates of polar bears are much higher at around 95% per year9 (source: Science Progress, Ø. Wiig, et al, Vol 21, No. 2, 2008).


4. Adults

The final stage is adulthood which is when the polar bears have become sexually mature and can have their own offspring.

Females mature before males, although most estimates of the age at which polar mature can vary widely, even when based on the same sub-population.

For example, A 2002 study in Greenland suggested that males became sexually mature in the spring after turning 5 whereas a 2007 study also in Greenland suggested it was from age 7. Both were reliable, published reviews in the same area.

In general, most studies suggest that males reach maturity sometime between ages 5-10 and females slightly younger between ages 4-6.

Polar bears that are malnourished may be nutritionally stressed, this can impact their reproductive success and survival10 (source: Science of the Total Environment, K.A. Patyk, et al, Vol 514, 2015).


Reproduction Cycle

The reproductive cycle of polar bears can be broken down into 4 key stages; mating (spring), denning (fall), birth (winter), and emerging from the den (winter).

Polar bears are often described as both polygynous and promiscuous. They will have many different mating partners during their lives and even during the same mating season11 (source: Canadian Journal of Zoology, E. Zeyl, et al, Vol 87, No. 12, 2009).

Male polar bears are not paternal and only stay with the female for a few days after mating. After giving birth, the female will remain with her litter for 2.5 years.

This means that females are only available for mating every 3 years, resulting in fierce competition among male polar bears during mating season. Fighting and injuries between males are very common.

Once their eggs have been fertilized, pregnant females will build up fat reserves ready to enter a maternity den as mentioned earlier. There is a delay between egg fertilization and implantation in the uterus for this reason (known as embryonic diapause).

This also means that multiple males can reproduce with the same female in a breeding cycle, so the female will often give birth to offspring from different fathers at the same time12 (source: Canadian Journal of Zoology, E. Zeyl, et al, Vol 87, No. 12, 2009). Most litters are between 1-3 cubs.


How Long Do Polar Bears Live?

Polar bears can live up to around 30 years in the wild. However, pup mortality is high and those that do make it to adulthood will rarely live past 15 years of age13 (source: Ursus, Ø. Wiig, Vol 10, 1998).

Common causes of death among polar bears are malnourishment, drowning, disease, and humans.

Additionally, cubs may die from hypothermia or cannibalism when they are hunted by adult male polar bears during times of food scarcity.

To find out more, see our full article on lifespan and causes of death among polar bears.


Related Questions

How Long Do Polar Bears Stay in their Dens?

Polar bears will stay in their dens for around 5-7 months during pregnancy. During this period they are in a hibernation-like state. Only pregnant female polar bears make dens, they are known as maternity dens.

How Many Babies Do Polar Bears Have?

Polar bears will usually have between 1-3 cubs in each litter. The mother stays with the cubs for 2.5 years after they are born so there are at least 3 years between each litter. Single-born cubs tend to be much larger than twins or triplets.