Hamsters, natural foragers, have mostly preventive defenses against predators in the wild -- enough to survive the ages. They adopted behaviors that allow them to scavenge for food without attracting the attention of larger animals and allow them to flee to safety when danger arises. Your pet protects himself the same way to any perceived threats in his domestic environment. He'd rather flee than fight; if pressed he'll bite.
If you've ever accidentally set your hamster loose in your home or had one escape from his cage or hamster ball, you probably already know hamsters' first defense against predators is flight -- they run away and hide. Hamsters are generally timid when exploring new environments, quick to flee back to an area they consider safe at the first sign of a predator. They have poor eyesight, relying on smells and sound to evaluate risk. A spooked hamster will run from a threat if possible; it's a hamster's best chance for protecting himself from a predator such as a cat.
If you have spent any amount of time observing your hamster in his cage, you know hamsters like to burrow deep into their bedding to build nests. Hamsters in the wild dig burrows for protection from weather extremes and predators. Hamsters hidden in burrows are less likely to be spotted by predators such as felines and birds of prey. Your hamster has no predators, save the cat, but burrowing is instinctive even in a domesticated rodent.
Hissing and Aggressive Postures
Generally, a hamster who feels threatened will put on an aggressive act before a pre-emptive attack. A hamster who is trying to protect himself from a threat may stand on his hind legs with his front paws out for protection, while an actively aggressive hamster will roll onto his back and bare his teeth. His legs will be up and ready to push away from whatever being he perceives as a predator intent on attacking him. A threatened hamster may hiss as well, as a warning. If you notice your hamster behaving in any of these ways, immediately stop handling him and leave him to himself.
Biting, a hamster's most dangerous weapon, is generally a last resort for protecting himself. Startling your hamster or accidentally hurting him will get you bit. Waking him from a sound sleep by picking him up will get you bit; instead, blow on him and talk to him to wake him. Bites from a hamster are painful but rarely lethal to humans or other predators, though you'll want to employ your vet if your hamster bites your dog or cat. Hamsters can bite and kill one another, which is why in most cases hamsters should be kept separate from one another.
- hamster on a nut image by Silvia Ottaviano from Fotolia.com