In the second book of The Shiva Trilogy by Amish Tripathi, The Secret Of The Nagas , it is stated that animals kill for only two reasons - hunger and self-defence. This is a belief that many people seem to believe but it is not true. Here are a few instances where non-human animals (I presume that's what the novel is referring to) kill for reasons other than hunger and self-defense.
- Lions kill cheetah cubs left and right. Studies from Serengeti indicate that lions may be responsible for up to 57% of cheetah cub mortality! And they don't eat them. It is shown a number of times on the nature channels.
- Infanticide is a powerful tool in ensuring the survival of a species, researchers are increasingly finding. For many animal infants, the greatest threat to their survival is from their own kind. It has been recorded in a number of species including mammals such as rodents and primates, and fish, insects and amphibians. Among lions, male interlopers attempt to overthrow the fathers of the cubs in a pride. If they succeed, by hurting, chasing off or even killing the dominant male, and taking over the leadership of their group, then infants are suddenly placed at great risk. The mothers will come into heat only if the cubs are dead and if the males wait, they may be overthrown by other males which will mean that their genes will not be passed on.
- About 20 percent of younger blue-footed booby siblings die because of their elders’ attentions. The nearby brown boobies kill their younger siblings every time. Being born a second child in a brown booby household is nearly a death sentence (unless the elder dies of a disease or something). Probably the only reason the parents have two chicks is to have an insurance in case the elder one doesn't survive.
- Some species of birds thrive not by carefully rearing their own young, but by pawning that task off on adults of other species. The European Cuckoo is the bird in which this habit has been most thoroughly studied. Female European Cuckoos lay their eggs only in the nests of other species of birds. A cuckoo egg usually closely mimics the eggs of the host (one of whose eggs is often removed by the cuckoo). The host incubates and hatches the cuckoo egg. Shortly after hatching, the young European Cuckoo instinctively shoves over the edge of the nest any solid object that it contacts. With the disappearance of their eggs and rightful young, the foster parents are free to devote all of their care to the young cuckoo. The cuckoo chick often grows much larger than the host adults long before it can care for itself but the host doesn't seem to notice it. Here is a video of what is called brood parasitism.
- I saw a program (narrated by David Attenborough) in which a group of killer whales chase a gray whale and its calf across a vast expanse of ocean. The long chase made the calf tired and the killer whales managed to isolate it from the mother. They then tore the calf to shreds and swam away without eating anything. The killing had been for fun.