Mechanism

How does it work?

Mechanism of the infanticide behavior in Polar bears refers to the physiological factors driving this behavior.

While it is clear that polar bears primarily target large animals such as ringed seals, and at times walruses, infanticide is also observed due to the decline in primary food sources. This drive for survival, which will be discussed in greater length in the Survival Value page, is physiologically driven by the bear's need to maintain homeostasis. However, while infanticide is a form of food intake, young cubs are not nutritive, especially when compared to the fat-rich seals. What is interesting about cases of infanticide is that once the male has gone through the risk of injury and killed the cub, the male doesn’t seem to readily consume the carcass. From this observation, infanticide is also believed to be a mechanism of density-dependent population regulation (Amstrup 2011). The frequency of infanticide and harassment of young males is higher in more populated areas.

Figure 1. Population and distribution map of Polar bears.

Because Infanticide is a behavior whose mechanisms can increase a male's relative fitness, the behavior is believed to occur between the breeding period and the emergence of cubs, due to the fact that there is no selective advantage to killing the offspring the male fathered (Derocher et al., 1999). In order to maximize the effects of this behavior, the male must keep track of the female after the death of the cubs, to be present for the onset of estrus. However, there have been two known cases in the Beaufort Sea, in which the male did not stay behind for the onset of estrus. In the first case, the male and female were separated by dozens of kilometers the day after the infanticide occurred, and they were headed in opposite directions (Amstrup et al., 2006). In another case, by the end of two weeks, the male was found to be more than 200 kilometers away from the female and highly unlikely that breeding was a goal for the male. These are, however, isolated cases, and can, therefore, not totally disprove the idea that the desire to breed and the onset of female esterus mechanistically drive the infanticide behavior. Additionally, infanticide isn’t likely due to the risk of injury from the defending female, so it is not simply a result of threatening male behavior, but the intent to kill the cubs, perhaps due to the desire to breed.