Squirrels are often viewed as harmless backyard wildlife, commonly seen gathering nuts and scampering through parks. However, the idea that a mother or a rival squirrel might kill its own young is shocking. This behavior, known as infanticide, is a documented occurrence in various squirrel species and requires a factual explanation.
Infanticide and Cannibalism in Squirrel Populations
Squirrels do engage in infanticide, the killing of dependent young, but it is not a routine part of their life cycle. This behavior sometimes leads to cannibalism, the consumption of the killed offspring. It is important to separate these two actions, as the killing is primarily a behavioral strategy, while the eating is often a secondary act for nutritional gain.
The perpetrator of infanticide varies, involving the mother, a rival male, or an unrelated adult. Parental infanticide occurs when a female kills her own young, typically when the kits are sick, injured, or represent a drain on resources needed for her survival. Nonparental infanticide is also observed, where an unrelated adult kills another’s young to eliminate future competition.
In studies of California ground squirrels, a majority of observed infanticide cases were committed by females, often followed by cannibalization. The consumption of the pup provides a nutritional benefit, acting as an alternative feeding strategy, especially when food is scarce. These acts are rare and occur under specific, high-stress conditions or in times of abundance for evolutionary advantage.
Environmental and Biological Triggers
Infanticide is rooted in evolutionary and environmental pressures that dictate survival and reproductive success. One documented cause is sexually selected infanticide, typically carried out by a male. This behavior is seen in red squirrels during “mast years,” when food resources, such as white spruce cones, are unusually abundant.
During these years of surplus, female squirrels are capable of having a second litter. A male will kill the pups of a rival male from the first litter to bring the female back into estrus, or reproductive readiness, more quickly. This action increases the killer male’s chances of fathering the second, larger litter, thereby maximizing his genetic contribution to the population.
Other triggers relate to resource conservation and disease prevention. A mother may abandon or kill a litter during periods of extreme resource scarcity, such as drought, to ensure her own survival so she can breed again later. Removing a sick or compromised pup prevents the spread of illness to the remaining healthy litter members. Human interference, such as touching a nestling, can also lead the mother to reject or abandon the young.
Typical Dietary Habits of Squirrels
Infanticide and cannibalism contrast sharply with the typical, day-to-day diet of a squirrel. Squirrels are classified as opportunistic omnivores, consuming both plant and animal matter and adapting their diet based on what is available. While often observed eating nuts, seeds, and fruits, their nutritional needs extend beyond these common items.
Their diet includes leaf buds, fungi, tree bark, and various vegetables, which they forage for throughout their territory. Squirrels also require protein, obtained by consuming insects, bird eggs, and small vertebrates. California ground squirrels have been documented actively hunting and eating voles, demonstrating carnivorous flexibility.
This varied and adaptive diet explains why cannibalism, while rare, can occur under duress, providing a high-protein meal in a survival situation. The behavior is a function of their underlying nutritional requirements and their opportunistic nature. Their ability to take advantage of various food sources helps them persist in changing environments.