THE IMPORTANCE OF NEST UTILIZATION AS A BEHAVIORAL THERMOREGULATORY STRATEGY IN SOREX MINUTUS THE PYGMY SHREW

1. We examined the importance of the behavioural thermoregulatory mech anism of nest utilization in one of the smallest temperate endotherms, Sorer minutus, the pygmy shrew and in particular, if there were any s easonal variations in the effect of nest use on metabolic rate. 2. VO2 was highly significantly related to ambient temperature, nest presenc e and season in S. minutus (ANOVA). Shrews that had the opportunity to utilize nests showed a reduction in VO2 of up to 20%, depending on se ason and ambient temperature. 3. VO2 in winter acclimatized shrews was significantly reduced when nests were provided at temperatures below thermoneutrality. Nest utilization did not affect VO2 at any temperatu re in summer acclimatized shrews. In adult spring shrews of both sexes , VO2 was only significantly reduced at low temperatures (10 degrees C ) when nests were used. 4. Nest utilization is an important behavioura l thermoregulatory strategy in S. minutus which should be taken into a ccount in estimations of daily energy expenditure.