Infanticide and cannibalism are rare but documented behaviors among polar bears. This disturbing intraspecies aggression is not a sign of malice, but rather an extreme response to severe environmental or biological pressures. The acts of killing and eating a conspecific, particularly a cub, are typically driven by a desperate need for calories or a powerful reproductive strategy.
Resource Scarcity and Survival
Cannibalism in polar bears is often an opportunistic event directly connected to nutritional stress, where the bear acts as a predator of convenience. These large carnivores rely almost entirely on hunting seals from the sea ice to maintain the massive fat reserves necessary for survival. When hunting opportunities fail, the resulting extreme hunger and energy deficit can lead a bear to view smaller conspecifics as a potential meal.
The consumption of a cub, which is an easy target with limited defense, provides a sudden, necessary intake of protein and fat that can sustain a starving adult bear. While large adult males are the most frequent perpetrators, nutritional stress is the primary reason for these attacks outside of the mating season. In extremely rare instances, a mother may consume her own cub, known as filicide, although this is usually only observed when the cub is already dead or dying due to other factors, suggesting a desperate attempt to recoup lost energy.
Reproductive Motivation in Males
Infanticide is also driven by the reproductive strategy of adult male polar bears. A female caring for cubs remains non-receptive to mating for an extended period, often two to three years, due to a hormonal state known as lactational amenorrhea. During the spring mating season, an adult male may kill unrelated dependent offspring to force the female back into estrus.
By eliminating the cubs, the male gains an immediate opportunity to mate and pass on his own genes. This sexually selected infanticide is a brutal but common strategy seen across many large carnivore species, including other bears and lions. The female’s ability to defend her young is a major determining factor in the success of the male’s attack, with larger and more experienced females having a better chance of warding off the threat.
Intensifying Factors: The Impact of Climate Change
The current climate crisis acts not as a direct cause of these behaviors, but as a powerful intensifier that increases their frequency and opportunity. Polar bears depend on stable, extensive sea ice as a platform for hunting seals. As the sea ice melts earlier and freezes later, the bears are forced to spend significantly more time on shore, away from their primary hunting grounds.
This extended period onshore intensifies nutritional stress by increasing the time bears must fast, pushing more individuals into the extreme hunger that drives opportunistic cannibalism. The loss of vast ice territories concentrates bears into smaller, fragmented habitats, leading to an increased proximity between unrelated adults and cubs. This greater interaction frequency provides more opportunities for adult males to encounter and kill cubs, leading to a documented increase in observed cases of infanticide and cannibalism in regions experiencing rapid sea ice loss.