Reading, P., Reading, R., Branstone, C. 2020. Mirror, mirror, on the wall. Animal Technology and Welfare 19(1), 98-100.

When mice are grouped together for the first time, it is a novel experience filled with new sights and smells that will stress the animal too much and may cause aggression. By adding a mirror prior to grouping, they become accustomed to the sight of another mouse. Scents cling to bedding and nesting material so swapping over both between mice being grouped also allows for them to be habituated to each other’s smells. By the time the mice are introduced they should be used to the sights and smells of another animal reducing stress and the likelihood of fighting. A mirror is placed inside each cage in a central position hanging from the grid using a hook. A handful of bedding and nesting material should be swapped over daily and placed by the mirror. This should be repeated for 2-3 days. On the final day the mice should be placed together in a clean cage with no mirror. Their cage should be left off of the rack and observed regularly on the first day. This method currently has a 78% success rate and has been used across a variety of different strains including different strain pairing. The mirror has been proven to be a vital part of the strategy as only 16% of non-mirror pairings were successful.