The influence of nest sharing on the expression of daily torpor in the white-footed mouse

During winter the white-footed mouse, Peromyscus leucopus noveboracensis, often becomes torpid when huddled with other mice. While some mice become torpid on a regular basis, others only infrequently, or never, become torpid. Mice acclimated to cold and to short daylength were monitored by direct observation and with radiotelemetry equipment to determine the influence of sharing a nest on the occurrence and body temperature characteristics of daily torpor. Similar numbers of individually caged mice and mice caged in groups of three became torpid at least once. The frequency of torpor (how often mice become torpid) was also similar for solitary and huddled animals. When mice known to enter torpor were caged in groups of three, usually huddlemates all became torpid (54%) or all remained euthermic (32%) on any particular day. Observations of "mixed" huddles (14%) of torpid and euthermic mice were less common, suggesting that physical disturbance by euthermic mice inhibits the expression of torpor in huddlemates. The individual body temperature profiles of torpid huddlemates were similar and resemble the characteristic profile reported for solitary mice. Moreover, perturbation in body temperature during torpor in one mouse often coincided with a similar adjustment in a torpid huddlemate.