Least chipmunk, Kootenai National Forest, Montana, United States (© Donald M. Jones/Minden Pictures)

In the world of woodland critters, the least chipmunk might seem like the 'under squirrel'—but don't count it out. With survival smarts and turbo-charged feet, this tiny rodent proves that being 'least' is no reason to squirrel away your potential. Weighing less than a deck of cards and measuring under 25 centimetres from nose to tail, this species is North America's smallest chipmunk.