Social thermoregulation in least shrews

Cryptotis parva exhibits a geographic range and ecological requirements unique among North American soricines: it possesses a latitudinal distribution, metabolism and communal nesting pattern more like the crocidurines of the eastern hemisphere. We utilized oxygen consumption (VO2) techniques to examine metabolic shifts and video to document activity patterns and dynamics of solitary and group nesting C. parva. Between ambient temperatures of 4°C and 34°C, solitary C. parva demonstrated an inverse relationship between ambient temperature (Ta) and resting metabolic rate (RMR); thermal neutral zone (TNZ) was very narrow, between a Ta of 34°C and 36°C. VO2 was measured in groups ranging in size from one to eight at Tas of 4°C, 14°C, 24°C and 34°C. The group size had a significant effect on the median RMR and median predicted Kleiber value and was more effective at reducing metabolic cost at a lower Ta. In a second experiment designed to assess the effects of huddling group size and incubator Ta on the Ta of the nest chamber, both had significant effects. Group size had significant effects on the Ta of the nest chamber at incubator temperatures of 5°C, 10°C, 15°C and 32°C, but not at 25°C. We found no behavioral or physiologic evidence of heterothermy.