Comments & suggestions  should be directed to jroese@lssu.edu Visit my website Behavior Mice are timid but social animals.  Contact with conspecifics (others of their species) is important and a mouse housed alone may become more aggressive.  Although wild mice are nocturnal, laboratory mice have active periods during both the day and night.  Categories of common behaviors of mice include: (1) maintenance behaviors (grooming, eating, drinking, nesting);  (2) investigative/exploratory behaviors (climbing, digging, chewing, sniffing); and (3) social interactions (huddling together, grooming one another, scent/territorial marking, aggression, defense, sexual behavior).  Mice spend a great deal of time manipulating their bedding material, and if the material allows they will build tunnels and nests.  Providing appropriate nesting materials to pregnant mice is important as the nesting behavior is very pronounced in mice. Behavior may be strain specific and variations in mouse behavior are becoming increasingly common with the advent of knockout and transgenic mouse strains.  In some strains, female mice will attack other females, a behavior that is normally uncommon.  Other strains may demonstrate poor nesting behavior, which results in decreased survival of the pups.  These behavior changes can affect the reproductive fitness of an individual strain and make production of additional genetically-modified animals difficult. “Barbering” is a common practice among mice caged together, especially males.  The socially dominant animal in the cage will selectively chew off the hair of its subordinates.  The missing hair is generally noticed on the head, neck and muzzle  but may also be missing from other parts of the body.  The skin of the barbered areas usually appears normal.  Barbering patterns may be strain related. Adult male mice housed together may be very aggressive towards one another.  Fighting among cage mates can result in bite wounds over the rump and back of the animal, and are generally more severe in the lowest ranking animals.  Separation of fighting animals is required and should be done immediately if a problem is suspected.  If male mice are to be housed together, they should be introduced to one another at the time of weaning, and not as mature adults. Mice that are startled or roughly handled may bite or pinch the handler's finger with their teeth, but in general mice are easy to handle (with some strain exceptions). Barbering - The socially dominant animal in a cage will often selectively chew off the hair of its subordinates. This is most common among males. The skin of the barbered areas usually appears normal. Bite wounds - Fighting among cage mates can result in bite wounds over the rump and back of the animal, and are generally more severe in the lowest ranking animals.