Shrinking Shrews

One of the challenges facing animals living in the world's temperate zones is how to survive winter, a time when food is often in short supply. Some deal with the issue by hibernating or migrating to warmer climes, and some invertebrates simply die off, leaving their eggs behind to hatch in the spring. The rest struggle through, something which can often lead to them losing body weight over the course of the season.

This is perhaps most obvious in animals that are naturally large to begin with. But, in 1938, German zoologist Georg Stein studied how winter affected the body weight of the smallest of mammals: shrews. He confirmed that they do, indeed, lose weight through the winter, despite already being unusually small. He was, in fact, impressed that they managed to survive at all, given how much food they normally require just to stay alive, their size requiring them to burn calories at a furious rate just to maintain their body temperature.