Surface area to volume ratio.

Example:- A hedgehog to a woodmouse.

There is a greater surface area to the woodmouse for the volume it has got.So if it is in a cold place it will call down quicker than the hedgehog. The hedgehog has less of a surface area but a greater volume to the woodmouse. So it is easier to keep the  core of the hedgehog warmer. So smaller animals will suffer more quickly. When we get a lot of snow bank and field voles and woodmice will stay under the snow as its actually warmer than being above it, they breathe by punching through the snow making little air holes. Stoats and weasels will suffer because they have lots of surface area to a very small volume.