Hissing is your hamster's way of telling you to stop, to leave him alone. A hissing hamster is indicating he may bite if you attempt to interact further. In order to have a happy relationship with your hamster, you will have to identify the reason he is hissing and correct the problem that is causing his behavior.
The Threatened Hamster
Hissing is an aggressive behavior that serves as a warning to anything your hamster views as predatory. Your hamster will hiss when he feels threatened. It is his way of warning a predator that he is prepared to defend. Hissing can be a precursor to aggressive posturing, such as laying on his back and baring his teeth, if not to actual biting with or without posturing.
The Sick Hamster
On occasion, a well-socialized, normally happy pet hamster will begin displaying aggressive behavior without any apparent reason for doing so. If your typically social hamster unexpectedly becomes aggressive, hissing included or not, it is possible he is in pain or not feeling well. Take your hamster to the veterinarian to determine if there is a medical reason for his aggressive behavior. If a physical problem is the root cause of your hamster's hissing or otherwise aggressive behavior, your veterinarian should be able to find and treat the problem.
The Frightened Hamster
Its fairly normal for a hamster who is not used to being handled by people to react negatively when you try to interact with him. A frightened hamster with very limited places to run and hide will feel more threatened than one who has a large cage with hiding spaces. Being taken by hand from the safety of his home is frightening for your hamster, not to mention the hand is invading his private space. Your hamster's hiss is his way of telling you he is scared of what you are doing and he wants you to stop. Socializing him properly will help alleviate the problem.
The Unsociable Hamster
Some hamsters react aggressively to being handled, perhaps because humans have handled them badly, causing fear or pain. Hamsters that belong to poorly supervised children can become aggressive after repeatedly sloppy handling, being dropped, being played with inappropriately or being otherwise tormented. Hissing is a natural reaction for a hamster who expects misery to be the direct result of being handled. Attempting to socialize a hamster that has learned that people are not his friends can be difficult to impossible, depending on the age of the hamster and the severity of the abuse. Plenty of time and patience are required to rehabilitate a hamster with severe trust issues before he stops hissing at you, and possibly even more before he accepts your companionship.
Socializing Your Hamster
Socializing your hamster takes time, gentle handling and patience. Hamsters are naturally shy and timid creatures. From the moment you initially handle your hamster, you must ensure he is not threatened by your presence and strive to make him realize he's safe with you. Provide food, water and bedding, and let the hamster alone for a few days. Then, holding a treat, allow your hamster to sniff your hand. Gently stroke his back after a few times, if he allows you to do so. If your hamster shows any sign of aggression, including hissing, stop what you are doing and revert to behavior your hamster is comfortable with. If your hamster hisses when you reach into his cage, try spending time interacting with him through the sides of the cage without actually sticking your hand in it. Talk to your hamster and give him treats through the cage. Take as much time as necessary until your hamster views you as a friendly presence instead of a pest. Placing a treat in your palm should eventually lead a hamster to climb aboard when you reach in. Do not pick your hamster up until he is comfortable with your handling him within his cage. Socializing your hamster properly so that he is not afraid of you will do a lot to prevent him from hissing at you.
Preventing Aggressive Behavior
The key to preventing hissing and other aggressive behavior is modifying your own behavior. If your hamster reacts aggressively to something you're doing by hissing or baring his teeth, stop doing it. Your hamster cannot use words to tell you he doesn't like your hand in his cage or that he'd rather not be picked up by your elementary school student. His hiss is no different than your "Stop!"
The key to preventing aggressive behavior such as hissing is making sure your hamster feels safe. Proper socialization will lead to his becoming trusting and accepting of your handling. Don't wake your hamster from a sound sleep or attempt to lift him out of the cage without supporting his body. Do not startle your hamster; he will be able to hear you if you speak gently to him. A hamster is not a toy. Supervise children when they handle hamsters and prevent them from playing with them in a manner that is inappropriate or is uncomfortable for a live animal.
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