Are there documented cases of mammals who have killed for apparently no reason (other than for fun)? Preferably cases that have a nice web-link to them?

Sorry for the dumb question. I've heard of cases of this happening (like with wolves), but was wondering if there were any well-documented cases of it.

I am not sure that you could say that an animal had killed for fun - as you do not know the animals motive for killing. I would say that most animals would kill through instinct, rather than for 'fun'.

I know when I was young, I had a few pet rabbits that were killed by a fox, one of the rabbits was eaten - so was clearly killed as prey, the other was just left. Although it seems as though the other rabbit was killed for fun as the fox did not eat it, it could be that the fox just has a killing instinct - and saw the rabbit as prey so killed it. Cats are also known to kill birds, rodents etc apparently for fun - although this may have the same reasons behind it as the fox that killed on instinct.

Animals may also kill for territorial reasons, or in defence.

In the wild, I am not sure there maybe some examples of this, but my gut feeling is that animals would only kill another animal if there was a reason for it.

I did find this article on the web, but I am not sure of it's scientific credibility... … ngdom.html

Killer whales are known to 'play' with seals and penguins before eating them.  However, I haven't hear of a case where the killer whale has played with it's food then left the carcass and not eaten in.

Peter's post made me think of something potentially important here.

It is actually quite common for predators to "play with their food". Watch any domestic cat that has cornered a mouse of bird and you'll see it happening. However, I'm not sure that we can really say that this is for "fun" which is obviously a human idea. "Play" is a way to learn and practise hunting skills, whether or not you want to say an animal also enjoys it depends on how far you are willing to accept/believe/argue that an animal's emotions can be stated in such human terms.

As another example there is also some great footage about of dolphins killing porpoises and appearing to "play" with them in the process. This is again thought to be functional behaviour in the sense that it gets rid of competitors (porpoises and dolphins both eat fish) and provides an opportunity for younger individuals to practice hunting/killing skills. To me it also looks like they are also having fun... but that may be just a human perspective (and is probably based in part on shape of a dolphin's mouth which always reminds people of a human smile!)

To add another anecdote, my family once raised quail and we had a cat that would spend a good deal of its time sitting by the quail cages. One day someone left a cage containing 20 quail unlocked. When we came back, we found that the cat had slaughtered all the quail, except for a couple that apparently managed to escape the carnage. Clearly, the cat did not eat all of them.

There have been a couple of studies that have demonstrated this sort of behavior in cats and attempted to explain it, although I can't lay my hands on them right now as they were done in the sixties (fifties?). In these studies, cats appeared to have an innnate hunting instinct that, if prevented from hunting for a long period of time, caused them, for want of a better word, to go crazy, whereupon when they were allowed to hunt, they killed far more than necessary or typical for them. It is worth noting that the cats that did this were ones that had been raised as hunters. Cats that had never hunted live prey growing up did not show this phenomenon.

I also had a couple of cats that would find crickets, tear their back legs off, and then bat them around until they died. These were adult, well-fed cats, and I think it significant that they lost interest in the crickets once the cricket stopped moving. From this and the dolphin/porpoise videos I have seen, I can only conclude that they are indeed just having fun. It can certainly be attributed to instinctual behavior that is training them to hunt or some other functional behavior just as Alistair says. However, it is also possible to attribute any action taken by humans in a similar manner. I conclude from this that either one accepts that human feelings are only instinctual responses, or that animals do sometimes enjoy assaulting and sometimes killing other animals just like humans do. It does not make sense to me to say that humans are unique in this respect.