Infanticide, where an adult zebra kills a young foal, is a documented behavior rooted in survival and reproductive strategies. Understanding this phenomenon requires examining the ecological pressures and biological drivers that shape animal actions.
Infanticide by New Stallions
A primary reason for infanticide among zebras involves the takeover of a harem by a new male. When a new stallion successfully displaces a resident male, he often targets the foals sired by his predecessor. This behavior is a reproductive strategy aimed at eliminating the offspring of a rival and accelerating the mares’ return to fertility. Mares that are nursing foals typically do not ovulate.
By killing a nursing foal, the new stallion causes the mare to cease lactation. This physiological change induces her to come into estrus sooner. This allows the new male to breed with the mare and sire his own offspring. Such actions directly increase the new stallion’s chances of passing on his genes, enhancing his reproductive success within the limited time he may hold dominance over the harem.
Maternal and Environmental Influences
Infanticide in zebras is not solely limited to male aggression; maternal and environmental influences also play a role. A mare might reject a foal that appears weak, sick, or deformed. This conserves resources by not investing energy in an offspring unlikely to survive, prioritizing the mare’s own survival and future reproductive potential.
Inexperienced young mothers may exhibit abnormal maternal behavior, contributing to the foal’s demise. Environmental stressors, such as drought, limited food availability, or predation pressure, can also influence a mare’s ability to sustain her foal. Under duress, a mare might abandon or harm her foal to improve her own chances of survival or to ensure the success of future offspring.
Understanding the Evolutionary Drivers
The occurrence of infanticide in zebras, particularly male-driven, is understood within the broader context of natural selection. This behavior, while appearing brutal, serves as an example of strategies that increase an individual’s reproductive fitness. For male zebras, quickly siring offspring outweighs the cost of killing existing young, ensuring their genetic contribution to future generations.
This behavior is not unique to zebras and is observed across various mammal species, including lions, primates, and rodents. In species where a few males compete for mating opportunities, infanticide becomes more common. Such actions highlight how evolutionary pressures favor traits that maximize an individual’s success in passing on genes, even if those traits involve aggressive interactions.