Season affects tolerance of cohabitation by deer mice

We measured the resting metabolic rates of Peromyscus maniculatus for 7 days before and 7 days following forced pairing in order to determine whether seasonal light cycles influenced the rates of behavioral and metabolic habituation of deer mice to cohabitation. We had earlier shown that winter photoperiod and/or huddling results in lower resting metabolic rates and core temperatures of deer mice. Seasonal photoperiods were simulated by conditioning wild-caught mice to 24-h light cycles with differing durations of light exposure during the 24 h day. These experiments demonstrated that winter mice adjusted their resting metabolic rates from solitary to huddling levels much more rapidly than summer mice. Initial, high metabolic rate responses of paired mice persisted much longer than expressions of agonistic behaviors between paired mice. We propose that winter photoperiod enables animals to more efficiently make the transition to spontaneous, amicable huddling as a winter acclimatization strategy.