Infanticide, the killing of dependent young by an adult of the same species, is a documented behavior in large solitary predators, including the tiger (Panthera tigris). This act, which seems contrary to the instinct for species survival, is rooted in complex evolutionary and biological drivers. The behavior is not random violence but a severe form of competition that profoundly influences the social ecology and reproductive success of tigers in the wild. This exploration dissects the scientific reasons behind tiger infanticide, examining the ultimate causes of this lethal interaction.
The Biological Context of Infanticide in Tigers
Tigers do kill cubs, and this behavior contributes to high mortality rates among young tigers in their natural habitats. Across various tiger populations, cub mortality can be 50% or more, with infanticide being a leading cause alongside starvation and disease. Observations primarily occur in the wild, providing the context of territoriality and reproductive pressure. This phenomenon is a recurring pattern observed throughout the Felidae family and other large carnivores. The scientific focus is on understanding the adaptive logic that drives an adult tiger to eliminate the offspring, linking the behavior to reproductive cycles and competitive strategies.
The Primary Strategy: Infanticide by Unrelated Males
The most frequent and scientifically studied form of infanticide in tigers is perpetrated by a male against cubs he did not father. This behavior is a direct manifestation of the “sexually selected infanticide” hypothesis, serving as an effective reproductive strategy for the male. When a new male takes over a territory, often displacing or killing the previous resident, he encounters a female whose cubs are genetically linked to his rival. The presence of suckling cubs prevents the female from entering estrus, the period when she is receptive to mating.
Tiger females typically have a long investment period, with a gestation of around 103 days and cubs remaining dependent for up to two years. As long as the mother is nursing, her body is physiologically incapable of becoming pregnant again, a condition called lactational anestrus. By killing the cubs, the male instantly terminates the mother’s lactation, which removes the hormonal block and prematurely triggers her estrus cycle. This lethal intervention can shorten the interval until the female is ready to conceive, potentially making her receptive again within five months of losing the litter.
This strategy dramatically increases the new male’s reproductive fitness by accelerating his opportunity to pass on his own genes. The act is purely a mechanism of genetic competition, ensuring the male does not waste time guarding a territory with a female who is raising another male’s offspring. For the mother, the death of her litter is a massive loss of energy and time, but from the male’s perspective, it is an efficient way to consolidate his territory and reproductive monopoly. This intense evolutionary pressure results in an ongoing conflict between the reproductive interests of the males and the survival efforts of the females.
Secondary Causes and Environmental Pressures
While the male takeover strategy is the main driver, infanticide can also arise from proximate causes related to environmental and survival pressures. Resource scarcity is a significant factor, as a mother may selectively eliminate one or more cubs to conserve resources for the stronger littermates. This behavior acts as a form of resource management, ensuring that the remaining young have a higher probability of survival when prey is scarce. The mother essentially cuts her losses to maximize the overall genetic return from the current breeding attempt.
Cubs may also be killed accidentally, particularly when a mother is inexperienced or when she is forced to move her offspring frequently due to human disturbance or territorial shifts. During transport, the mother carries the small cubs in her mouth, and an accidental bite or misstep can result in fatal injury. Furthermore, if a cub is born with a severe physical disability or illness, the mother may kill it, preventing the investment of limited resources in an offspring with a low chance of survival. These instances are less frequent than male-driven infanticide but highlight the various pressures that influence cub mortality in the wild.
Maternal Infanticide and Protective Behaviors
Maternal infanticide, where a tigress kills her own cub, is the rarest form of this behavior and often occurs under extreme conditions. First-time mothers, for example, may be overwhelmed or stressed, leading to accidental injury or abandonment. Hormonal imbalances following birth can also disrupt maternal instincts, particularly in captive settings where environmental stressors are present. In the wild, a mother may also consume a dead cub to regain lost energy or to eliminate the carcass, preventing the scent from attracting other predators to the den site.
Paradoxically, the female tiger also invests heavily in counter-strategies to protect her lineage. Tigresses aggressively defend their dens and cubs against any intruder, including the resident male if he poses a threat to the offspring. They carefully select hidden den sites and frequently move the cubs to evade detection by infanticidal males. In some cases, a female may even mate with multiple males, a behavior that confuses paternity and may dissuade a potential killer, as a male is less likely to kill a cub that could potentially be his own. This struggle between male reproductive ambition and female protective defense is a defining feature of the tiger’s reproductive ecology.