Animal violence

People who love animals often think of animals as being aggressive but not violent. Only humans, they'll tell you, commit rapes, murders, or wage wars.
But that turns out not to be true. Some chimpanzees actually fight what Jaak Panksepp calls mini-wars. This is organized violent behavior.
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Many animals can be horrifically violent for no reason, it seems, other than the sheer desire to kill and maybe even to torture. It took many, many years for people to finally realize that dolphins, for instance, aren't he benign, perpetually smiling sea creatures they look like to us. Instead, dolphins are big-brained animal who commit gang rape, brutal killing of dolphin "children", and the mass murder of porpoises. In her book To Touch a Wild Dolphin, Rachel Smolker writes that male dolphins stick together in gangs and will chase a female down and forcibly mate her.

Temple Grandin: Animals in Translation