Couple of things about animals in W4. All animals can break building signs, and if you're in a boat , they will turn around and run away. Obviously this is intended and it makes animals more interesting.
If the animal is trapped by signs before you engage it in combat from a boat, it will neither break the signs or run away, letting you sling them to death from safety. This is probably a bug, but as far a I know it's also standard hunting technique for people without combat stats.
Second, bears don't follow this behavior. If you're in a boat, they stand on the shore and stare at you like animals used to do in W3, but unlike in W3 they do not run at low HP. You can kill bears by just slinging them to death from the river without any complications, they just wait to die and hand you 18k LP. This has to be a bug, bears shouldn't be easier to hunt than boars or foxes.
*edit: Can't actually confirm they break fences too, I've only heard that anecdotally and haven't tried it myself. Best to be clear.