Mice do not readily cross open spaces, as confirmed by utilisation of cage space studies. Mice are capable of assuming a wide range of social organisations and intense territoriality may be seen in reproductively active males. Pregnant and lactating females may prove aggressive in nest defence. As mice, particularly albino strains, have poor sight they rely heavily on the sense of smell and create patterns of urine markings in their environment. Rat As the rat is a very much more social animal than the mouse disruption to social groups should be minimised.
Rats are excellent climbers, avoid open spaces, and use urine spotting as a territorial marker.
The senses of smell and hearing are highly developed, and these animals are particularly sensitive to ultrasound. Daylight vision is poor, but dim-light vision is effective in some pigmented strains. Activity is higher during hours of darkness. This species is very different from the rat and the mouse. The female is larger and more aggressive than the male.