When a mother squirrel gives birth, she will usually have one or more extra nests prepared in addition to her birth nest. This way, if the birth nest becomes damaged or infested, or if a predator comes too close, she can quickly move her young to a new, safer location. The extra nests will be close enough for her to quickly make the move, but at a great enough distance to offer a safe refuge from a predator.
How she accomplishes this is amazing. The mother squirrel will grasp each baby firmly but gently in her mouth, one at a time, by the abdomen. Instinctively, the baby will curl up and hold on to the mother's neck with its paws. The mother then carries the pup at a full run, up and down tree trunks and jumping from branch to branch, to the new nest. She can move an entire litter this way in less than ten minutes if necessary.