Cannibalism in the animal world is usually a result of a lack of nutrition. It can be witnessed when a dog or a cat that has recently given birth, may pick off and eat the runt of the litter - it is to recover some of the energy that they spent during the birthing process.

I used to raise hamsters, and it was normal to have a few of the tinies eaten.. until I started making sure tunafish was regularly available in their cages during the birthing days. Now instead of eating the babies they run for the tunafish, leaving all the babies alive. I figured out early on that the normal hamster food just doesn't have the protein they need during that time.