On Monday, news reports suggested that in a suspected act of cannibalism, a tiger may have killed and eaten a tigress in Kanha Tiger Reserve of Madhya Pradesh. The news agency PTI quoted Kanha field director K Krishnamurthy as saying that "circumstantial evidence suggests that the tiger, during a territorial fight, dragged the tigress for about 700 metres". How frequently do animals feed on their own?
First thing first. The deceased Kanha tigress was unlikely to have been the victim of a tiger. A male tiger has no reason to eliminate a mating option, unless she was defending her cubs.
The remains showed that even the innards and almost the entire skin were missing. Tigers may not be picky, but they do not eat dirty. Barely anything was left of the carcass; even the large bones were picked clean. That would require a range of scavengers to take turns, but the freshness of the skull did not allow for so much time. The carcass looked a mystery, but it did not justify a cannibal tale. Because cannibalism is rare - and often occurs, when it does, under unusual circumstances.
Eating each other
Cannibalistic behaviour has been recorded in less than 2,000 out of over a million formally described species on earth. In species that are not naturally cannibalistic, it can be triggered by a scarcity of resources or the urge to push one's genes.
Yet, cannibalism is not unnatural. It is well known that praying mantises eat their partners during sex to maximise egg output. Cane toad tadpoles gorge on the eggs of their species to preempt competition. Every desert spider mom regurgitates food to help her young ones grow until she serves herself up to be devoured alive.
Evidently, nature does not consider it as "ungodly" as we do. The cannibal morph of tiger salamanders feed on the non-cannibal ones for extra nutrition. Embryonic Lamnoid sharks feast on their smaller siblings inside the mother's womb to grow fast and maximise their chances of survival after birth.
Particularly among large carnivores, though, the risk of pathogen transmission limits cannibalistic behaviour. Recent studies, however, suggest that cannibalism may actually reduce the prevalence of parasites by reducing the number of susceptible hosts. While that debate continues, cannibalistic behaviour is well documented among cats, both domestic and wild, under certain circumstances.
Cats eating cats
All male cats are wired to kill the offspring of another cat. The purpose is to deny rival male cats reproductive success and establish one's own bloodline. A female cat returns to oestrus (a sexually receptive and fertile state) immediately after losing her cubs and the murderous male can mate to give his genes a chance. When a male kills his rival's cubs, records show, he often ends up consuming them.
A cat mother, though, will fight tooth and nail to defend her kittens or cubs. While a tiger has no incentive for killing a tigress and reduce his breeding options, a defending mother may push it and fight to death. In April 2009, Ranthambhore's Berdha female (T4) died defending her adolescent cubs. Her sacrifice was not wasted as both her offspring - T40 male and T41 female - survived.
Fights among two adult tigers of the same sex may also lead to cannibalism. A dominant tiger seeks to eliminate weaker males and become the only mating option for the tigresses in the vicinity. Tigresses may fight over prime territories and access to resources but these battles rarely turn fatal.
Cat moms may themselves kill their offspring under unusual conditions. If resources are limited, she may eliminate the weaker cubs to focus on the survival of those that stand a better chance. It is also possible that a cat under stress will reflexively direct the aggression to her cubs. There are instances of captive leopards chewing up their cubs delivered inside trap cages exposed to people.
In none of these cases, cannibalism is driven by hunger. Carnivores rarely consume another carnivore as food. But the very act of killing involves a heightened aggression that can make a predator get into an involuntary mode where it starts eating what it has killed. Going by eyewitness accounts, Ranthambhore's tigress Machhli partially consumed a marsh crocodile it famously vanquished. There are recorded instances of tigers and leopards biting into a territorial rival they killed.
In most of these recorded instances, the big cats did not finish the meal and, probably as the hormones settled, moved on. In a rare case or two, leopards did return to feed on leopard carcasses. But there is not enough to suggest that the predatory behaviour of big cats include cannibalism.
That is why Kanha's tigress carcass, whether or not consumed by a big cat, makes an unlikely case for tiger-eating tigers in the prowl. Conservation is anyway a fraught battle and does not require imaginary threats.