The squirrel family, Sciuridae, is a diverse group of rodents including over 280 recognized species. These animals range widely in size, from the tiny African pygmy squirrel to the much larger marmots. Understanding where squirrels are found requires examining their expansive global reach and the specific habitats dictated by their distinct lifestyles.
Global Presence and Diversity
Squirrels are native to nearly every terrestrial environment worldwide, demonstrating a remarkable capacity for habitat colonization. They are indigenous to the Americas, Eurasia, and Africa, having successfully diversified across temperate, tropical, and even polar regions. The only continents where squirrels are not naturally found are Australia, where a few species were introduced by humans, and the frigid expanse of Antarctica.
The Sciuridae family contains approximately 285 species, occupying habitats ranging from arctic tundra and high-altitude montane forests to tropical rainforests and arid grasslands. This global distribution highlights the family’s evolutionary success and its ability to adapt to extremely different climatic conditions and ecological niches.
Distribution by Ecological Group
The broad distribution of the Sciuridae family is best understood by dividing its members into three primary ecological groups: tree, ground, and flying squirrels. Each group has evolved specialized physical features and behaviors that confine its members to specific geographic and environmental zones.
Tree Squirrels
Tree squirrels, primarily represented by the genus Sciurus, are widely distributed in forested regions globally, excluding the Australasian and southern South American continents. Their presence is contingent upon the existence of trees, which they use for shelter, escape from predators, and foraging. These squirrels thrive in various canopy structures, from temperate forests dominated by oak and hickory to tropical rainforests and swamp environments.
The genus Sciurus has a significant presence in the New World, with numerous species ranging throughout North America, Central America, and the northern part of South America. In the Old World, tree squirrels are found across northern Eurasia, parts of the Middle East, and Japan. Their arboreal lifestyle requires forest habitats that provide a consistent supply of hard mast, such as nuts and acorns, which form the dietary basis for many species.
Ground Squirrels
Ground squirrels represent the most geographically diverse group, inhabiting open ecosystems across North America, Africa, and Eurasia. Unlike their tree-dwelling relatives, their distribution is centered on landscapes that permit burrowing and offer open sightlines for predator detection. This group includes well-known genera such as the marmots, prairie dogs, and chipmunks.
These fossorial species occupy expansive areas including arid grasslands, open pastures, rocky slopes, and arctic tundra. Marmots are often found in high-elevation alpine meadows and mountainous terrain. Prairie dogs are restricted to the short-grass and mixed-grass prairies of North America, where their complex burrow systems shape the ecosystem.
Chipmunks, while often seen climbing trees, spend most of their time foraging and nesting in underground burrows. They are distributed across forested and shrubland areas of North America and parts of Asia.
Flying Squirrels
The distribution of flying squirrels is tightly constrained by their reliance on continuous tree cover for their gliding locomotion. These nocturnal species are found in the dense forest canopies of North America, Eurasia, and especially the temperate and tropical forests of Asia. The presence of a gliding membrane necessitates a habitat structure that allows for long-distance travel between trees.
In North America, species like the northern and southern flying squirrels inhabit deciduous and coniferous forests from Canada down to the southern United States. However, the majority of the over 50 flying squirrel species are concentrated in Asia, occupying tropical rainforests and dense woodland environments. Their distribution is limited to areas with sufficiently tall and close-set trees to support long glides.
Specific Habitat Requirements and Adaptations
A squirrel’s ability to establish a territory is determined by micro-habitat conditions that satisfy its needs for shelter and food security. The structural complexity of a forest is important for arboreal species, requiring canopy connectivity for efficient movement and vertical escape routes from ground predators. Tree squirrels rely on natural tree cavities, snags, and abandoned woodpecker holes for nesting, or they construct spherical nests, known as dreys, from leaves and twigs on branches.
The requirements for ground-dwelling species are centered on soil composition and terrain features conducive to extensive burrow networks. Fossorial squirrels require soils that are well-drained and relatively easy to dig, which is why many species prefer dry, open areas like prairies and deserts. In contrast, the largest ground squirrels, the marmots, are adapted to the cold, high-altitude environment of alpine zones, where they use deep burrows for hibernation.
Climatic extremes also influence distribution, especially for species that must cope with prolonged periods of scarcity or cold. Ground squirrels in temperate zones, for example, exhibit a physiological adaptation called hibernation to survive winter, while some species in hot, arid regions enter a similar state called estivation during the hottest parts of the summer. This ability to regulate metabolism allows these animals to inhabit regions with marked seasonal variation, such as the arctic tundra or desert edges.
Many squirrel species have expanded their distribution into human-dominated landscapes through behavioral adjustment. Tree squirrels, particularly the eastern gray squirrel, utilize urban parks, gardens, and residential areas by adapting human structures as proxies for their natural habitat. They frequently use attics, roofs, and walls as den sites, substituting man-made cavities for natural tree hollows.
This adaptation includes a decrease in wariness toward humans, allowing them to exploit human-provided food sources. They thrive in environments where natural predation pressure is often reduced.