"All the world will be your enemy, Prince of a Thousand enemies. And when they catch you, they will kill you. But first they must catch you; digger, listener, runner, Prince with the swift warning. Be cunning, and full of tricks, and your people will never be destroyed."
- Frith

There a lot of predators out there Frith created to hunt and kill rabbits; like foxes, snakes, birds of prey, weasels, badgers, cats, dogs, stoats, and many other carnivores, and most of all, Man, who also hunt for rabbits.

Some of the predators somehow learned to talk in the same language as the rabbits or speak in hedgerow, like cats or weasels. And they could be the only enemy besides General Woundwort that would threaten a rabbit's life, or warren, in my opinion.