It has been written that squirrels have the highest ratio of brain mass to total body mass of any mammal, including humans, so it should be no surprise that their interactions and ability to adapt are so advanced. They live happily in the densest wildernesses and the most populous cities, they can find their stashes of buried nuts months after caching them away, and they can manage to maintain both winter dens and summer dreys without forgetting what they need where.
Squirrels ordinarily bear their young in the Spring, when the gathering is good, but sometimes in the Fall. They live only eight to ten years, so they have to grow up fast.
Like humans’ forebears, squirrels spend most of their lives building or repairing their habitats, foraging for food, and trying to avoid being some other creature’s supper. They are herbivorous (again like humans’ forebears again), eating the nuts, buds, flowers and seeds of deciduous trees, the cones and new growth of pines and other conifers-- and the largesse of humans.
For Summer, squirrels build dreys near the ends of tree limbs and branches, made of interlaced twigs, leaves and whatever else comes to paw, and they are very securely rigged. (Did you ever see a squirrel’s nest that had fallen from a tree, as you do birds’ nests?) The dreys are waterproof and insulated with moss, bark, leaves, fur, feathers and other soft materials foraged from the local environment. But for Winter, squirrels make larger, better-insulated dreys closer in on tree limbs or, vacancies permitting, they make dens in cavities in the trunks of trees.
The most common squirrels in the United States are gray squirrels, which are indigenous. There also are black squirrels, which are said to have originated in Germany and Eastern Europe and are fairly rare in the United States. And then there are red squirrels, said to have arrived with early settlers from Scotland. Red squirrels are smaller than gray or black squirrels, are very rare indeed in the United States, and are endangered even in their native Scotland, where Glamis Castle hosts a “Save Scotland’s Red Squirrels” Week each October.