Geometrical aspects of the energetic effectiveness of huddling in small mammals

Reduced energy expenditure resulting from huddling in small mammals is mainly attributed to the reduced surface area/volume ratio of the huddling group. Here we propose a model to account for the reduction of the relative exposed area of grouped animals and for the diminution of metabolic rate during huddling. We attempt to explain mechanistically how changes in energy savings may operate. We applied our model to results obtained by grouping deformable bodies, and also laboratory measurements of oxygen consumption on huddling small mammals of four species, We found a small amount of diversity in the energetic efficiency of huddling. We estimate that the average relative area lost during huddling ranged between 28.7 and 39.1%. The average huddling effectiveness in the studied species was 42%, which is a significant fraction of the energy/matter budget of a small mammal, especially under winter conditions.