The effect of ambient temperature on body temperature and on ultrasonic behaviour in litters of albino laboratory mice deprived of their mothers

Litters of mouse pups of various ages when deprived of their mother and kept for one hour at ambient temperatures of 3°C, 12°C and 22°C lose heat less rapidly than pups isolated individually at similar temperatures. The litters are able to maintain constant body temperatures of 35–37°C by day 8 at 22°C, by day 19 at 12°C and by day 21 at 3°C. Very little ultrasound is detected from litters of any age up to 21 days at 22°C while at 12°C ultrasound is mainly detected from pups of 4 and 6 days; very few calls are produced by older pups at this temperature. Considerably more calls are emitted at 3°C than at either of the two higher temperatures. At 3°C the total number of calls emitted during the hour-long exposure period varied markedly with age. There were two peaks of calling, one on day 6 and the other on day 16. The temporal pattern of calling throughout the hour-long exposure period at 3°C was similar in pups of 4 and 6 days and in pups of 8, 10, 12, 14 and 16 days, but differed between these two groups. In the younger group of pups the rate of calling rose to a peak and then decreased to zero as the pups became comatose; in the older pups the rate of calling was low initially then either rose throughout the rest of the hour or rose to a high level that was maintained. It is suggested that the various patterns of ultrasonic calling can be associated with the physiological development of mouse litters.