The Contributions of Local Heating and Reducing Exposed Surface Area to the Energetic Benefits of Huddling by Short-Tailed Field Voles (Microtus agrestis)

Many small mammals save energy by huddling. Huddling reduces the collective surface area exposed to the local environment and may heat the local environment. Consequently, huddling groups save energy, but the relative importance of reducing exposed surface area and local heating is largely undocumented. Oxygen consumption was measured in groups of Microtus agrestis Linnaeus consisting of five individuals, over a range of temperatures below thermoneutrality. Behavior was recorded simultaneously. Each group was measured when allowed to huddle and when prevented from huddling by partitions in the metabolism chamber. Local heating of the environment was correlated with temperature outside the metabolism chamber (outside temperature)for both huddling and separated groups, but local heating by huddling groups was significantly greater. At 0° C, local heating was 11.8° C and 5.8° C for huddling and separated groups, respectively. At the same outside temperature, O₂ consumption of huddling groups was lower than for separated groups (23% lower at 0° C). At 0° C, local heating accounted for about 55% of the total energy savings of the huddling group. Thus, local heating is a major component of the energy savings associated with huddling