Excessive grooming sometimes occurs when rodents are nervous. A mouse may wash its face continually if it feels insecure. Whilst this looks cute, continuous, vigorous face washing is a sign that the mouse should be left undisturbed for a while. ‘Barbering’ occurs when a mouse nibbles away patches of fur – from its own body, or that of another mouse. You may notice short patches of fur, but no irritation to the skin. It is a habit, like nail-biting in humans, which tends to get worse when the animal is nervous.
Concentrate on keeping the affected mice happy (e.g. see section on ‘environmental enrichment’ in 2b), but do not worry about this habit. It is only a nuisance if you wish to breed or show mice. The habit is often hereditary, so ‘barbers’ should not be bred from. Mice groom each other with their teeth. Grooming can sometimes be a way of expressing dominance (working out who is boss), or friendship. You may see one mouse holding another with its hands, whilst appearing to nibble at its fur. This is nothing to worry about, even if the mouse which is being groomed squeaks and doesn’t appear to like it. Playing: no squeaks, or very quiet ones.
Mice may play ‘catch’ and chase each other, but no wounds, and no signs of stress or ill health, will be seen. Young mice tend to be more playful than older ones – it is rare for mice younger than 3 months or so to truly fight. When mice fight seriously enough for it to be a problem, you will usually hear loud squeaking and see blood or scratches on the skin when you stroke the fur against the direction of growth. Note that loud squeaking often occurs when mice scrap or argue, without serious fights occurring.
Fighting looks quite different from grooming behavior – the mice will usually run around, perhaps one or both jumping towards the other with tail twitching angrily, or fur fluffed up. One or both mice may run off to get ‘time out’ and may look fed up. One mouse may seem to chase the other constantly.
Fighting is most common when the cage has just been cleaned, as mice reestablish their individual territories and dominance within it. Female mice tend to fight for a few days after a newcomer is introduced, as each mouse has to reestablish her place in the hierarchy. Male mice often fight in attempts to move up the hierarchy.
It is common to hear regular banter coming from a cage of male mice. Give the community as much space as possible – at least 24″x12″ for between two and six male mice – and lots of small hiding places so that each mouse can have his own territory. Fighting is something of a hobby for male mice – you do not need to separate them unless one has a bleeding wound or appears stressed.
If the level of fighting is unacceptable, your first move should be to look for a larger home for the mice. Small wire cages can be extended by attaching other cages, for example.
Please think carefully before separating the community. You may be condemning one of your mice to a life of solitary confinement. Splitting the mice up for ‘time out’ is not a good idea – it will probably be much harder to reintroduce them, than it would have been to leave them all together.
If you have several male mice, and fighting or bullying is making one miserable, try removing the most aggressive mouse – the bully – and leaving the victim in with the others.
If you just remove the victim of bullying, the bully may find someone else to pick on.