Polar bears, brown bears, and black bears are all known to sometimes kill and eat cubs, not just those of other fathers, but also their own. They’re known to commit infanticide and cannibalism to a certain degree.
Male bears kill cubs for various reasons.
They may kill the offspring of their competitors in order to mate with the females that become fertile soon after parting ways with their cubs or because there’s food scarcity, a common behavior seen in polar bears.
As cannibalistic animals, bears often fall victims to predatory and larger bears. For hungry bears, small cubs may be a nutritious and easy source of calories.
Infanticide isn’t only present in bears, but in other species like mountain lions and bobcats too.
Why Male Bears Commit Infanticide?
Bear infanticide happens during breeding season when male bears want to mate with the females that are fertile after leaving their cubs. It may also happen due to hunger, when bear cubs are sometimes the only source of calories.
Here are some of the theories proposed as potential explanations for this phenomenon:
1. To Gain Mating Advantage
Sexually selective infanticide is a theory that claims male bears kill and eat cubs to stop lactation in their mothers so the female bear could go back to heat and they could mate.
It’s only an SSI if certain requirements are met, i.e., the males kill the cubs which they haven’t fathered (otherwise it’s cannibalism), the mothers of the killed cubs go into estrus shortly after they’ve lost their offspring, and the male that commits the kill has a high chance of being the father of the mother’s next cubs.
This isn’t a flawless theory as there’s no guarantee that the male will achieve mating with the bear whose cubs it killed.
Moreover, a bear that goes back into the fertile phase isn’t a guarantee that the bear that committed the infanticide will be the one mating with the female.
Namely, there may be more potent male bears in their range that may fight the other male bear. What’s more, infanticide isn’t exclusive to the mating season.
Read More: Do Bears Mate for Life?
2. Extreme Hunger
Being cannibalistic animals, bears can eat cubs and smaller females when they’re extremely hungry. Cubs are smaller in size and less capable of defending themselves and therefore are a nutritious and easy caloric source of food for males.
This is a phenomenon long known to the natives of the Arctic.
During hard times, polar bear males cannibalize their cubs. A phenomenon studied since the 80s, it’s claimed by scientists to be committed by polar bears in late summer and autumn when seal availability drops.
Sometimes, the only thing they have to eat are the cubs, explains Ian Stirling, a biologist from the University of Alberta and Environment Canada.
Related Article: Do Bears Eat Wolves?
3. To Eliminate Competition
This hypothesis points out that infanticide among male bears could be a method of reducing competition.
One thing’s for sure: there’s plenty of competition in the world of bears, including competition for food, range, breeding, etc.
Some of the proponents of this hypothesis emphasize that sometimes bears may kill other bears that are younger and less dominant to lower their competition and ensure their own survival.
Joseph Classen, published author who runs the Wild Revelation blog notes that he personally witnessed this behavior while working in the coastal regions of Alaska.
An aggressive male brown bear killed several bears in the area during the summer. These bears weren’t cubs, there were a lot of fish in the rivers, and the bear didn’t eat its kills.
Maybe its goal was to decrease competition, but this can’t be known for sure.
This footage from Alaska shows a polar bear in Svalbard that committed infanticide and cannibalism:
Read Also: Rhino vs Bear
Do Female Bears Commit Infanticide?
Female bears don’t commit infanticide, this is exclusively seen in male bears during the mating season.
Female bears are actually highly protective of their cubs, especially in the period during which they care for them.
Mother bears are known to risk their own lives to keep their cubs safe, often from infanticide. Only a few sights are as scary as a strange male bear for mother bears.
Adult male bears often kill cubs that aren’t their own. After giving birth to her cubs, a female bear will often move far away from male territory and seek the best habitat for her and her cubs.
Related Article: Do Bears Get Stung by Bees?
Some researchers hypothesize that female bears often go near human regions with their cubs as a reproductive strategy: they’re far from the males whereas humans tend to fear them.
To test out this theory, Sam Steyaert, a wildlife biologist at NMBU led a study together with other scientists published in the Proceedings of the Royal Society B. It was concluded that the female bears remained closer to human areas with their cubs and in a way, they used humans as a shield.
Mother bears will choose dense vegetation, particularly when close to humans. In this way, they’re away from males and the humans don’t know they’re there. When hunting and killing bears, mothers and their cubs aren’t targeted by hunters.
This video shows how fiercely female bears fight to protect their cubs:
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It’s not uncommon for various species of male bears to kill cubs that aren’t their own; some even kill and eat their own cubs, like the polar bear. When food scarcity arises, the male polar bear will kill and eat its cubs.
Some scientists note that polar bears may resort to extreme cannibalism more and more due to climate change and food scarcity.
Bear infanticide is exclusive to male bears and it can be of various types, i.e., sexual infanticide (male bear kills cubs that aren’t his in order to mate with their mother), hunger (polar bears are known to kill and eat their own cubs when lacking food), or eliminating competition.
On the other hand, female bears aren’t known to eat cubs. They’re actually highly protective of them and often seek the best area to hide with the cubs and prevent infanticide.
This phenomenon isn’t the case in bears only; many other species commit it, including bobcats and mountain lions.
Stuart is the editor of Fauna Facts. He edits our writers’ work as well as contributing his own content. Stuart is passionate about sustainable farming and animal welfare and has written extensively on cows and geese for the site.