The feet, which include an often poorly developed thumb, have soft pads on the undersides[14] and versatile, sturdy claws for grasping and climbing.

They do so by rotating their ankles 180 degrees, enabling the hind feet to point backward and thus grip the tree bark from the opposite direction.

[20] When the squirrel sits upright, its tail folded up its back may stop predators looking from behind from seeing the characteristic shape of a small mammal.

[22] Premature death may occur when a nest falls from the tree, in which case the mother may abandon her young if their body temperature is not correct.

Squirrels mate either once or twice a year and, following a gestation period of three to six weeks, give birth to a number of offspring that varies by species.

[27] In temperate regions, squirrels commonly cache nuts beneath leaf litter, inside hollow trees, or underground.

[28] However, in subtropical and humid environments, traditional caching can lead to mold growth, decomposition, or premature germination.

[29] This behavior, believed to minimize fungal infections and reduce the risk of food loss, also inadvertently aids certain trees, like Cyclobalanopsis, in expanding their range, with forgotten or dislodged nuts sprouting in new locations, influencing forest ecology.

In temperate regions, early spring is the hardest time of year for squirrels because the nuts they buried are beginning to sprout (and thus are no longer available to eat), while many of the usual food sources are not yet available.

Squirrels, being primarily herbivores, eat a wide variety of plants, as well as nuts, seeds, conifer cones, fruits, fungi, and green vegetation.

This gradual process of successful interaction is called synurbanization, wherein squirrels lose their inherent fear of humans in an urban environment.

[34] When squirrels were almost completely eradicated during the Industrial Revolution in New York, they were later re-introduced to "entertain and remind" humans of nature.

The squirrel blended into the urban environment so efficiently that when synanthropic behavior stops (i.e. people do not leave trash outside during particularly cold winters), they can become aggressive in their search for food.

The distribution and diversity of such ancient and ancestral forms suggest the squirrels as a group may have originated in North America.