To keep warm and not fall too deeply asleep at night, she had to listen to the wisdom of the squirrels. In the fall, squirrels built a nest inside a hollow tree and lined it with leaves. The more leaves they put in, the warmer it was. This was the learning passed down through the tribe from the first ones.

It took a long time to find a hollow tree big enough for LittlestOne. When she crawled inside, she had just enough room to lie down curled up in a ball. She collected lots of leaves and dry grass from beneath the snow and stuffed them inside.

--from Long Winter's Nap, originally published in Analog Science Fiction and Fact, December, 2006