The image of a squirrel is often a small, bushy-tailed animal scampering up a tree trunk. This perception leads many to assume that all members of the squirrel family live exclusively in the canopy. However, the term “squirrel” is broad, encompassing many species with widely different lifestyles. A large and distinct group of these rodents are obligate burrowers, spending the majority of their lives beneath the surface.
Ground Squirrels and Their Habitats
The Sciuridae family includes the Marmotini tribe, which contains species known as ground squirrels, prairie dogs, marmots, and chipmunks. Unlike tree squirrels, these ground-dwelling species are adapted to a subterranean existence. Their physical form is less bushy-tailed and more robust, making them better suited for digging and navigating tunnels than for climbing trees.
These burrowing rodents are typically found in open, low-vegetation habitats such as fields, pastures, and rocky outcrops. They prefer environments where they can stand upright to scan for predators. Their reliance on open ground means they spend their lives close to their protective burrows. When threatened, a ground squirrel immediately darts to its nearest burrow entrance.
Structure and Purpose of Underground Burrows
Ground squirrels construct extensive, complex burrow systems that serve as a multi-purpose underground home. These networks consist of multiple tunnels and chambers, with systems commonly ranging from five to thirty feet in length, reaching depths of one to six feet below the surface. A single colony’s system may feature five to twenty entrances, providing multiple escape routes from predators.
The interior architecture of a burrow is highly specialized, containing distinct areas for different functions. There are chambers lined with grass for sleeping and rearing young, dedicated spaces for storing cached food supplies, and separate latrine areas. The burrow’s most significant function is providing a stable microclimate, offering protection from extreme temperatures and predators.
For many ground squirrel species, the burrow is also the site of deep hibernation, or torpor, which can last four to eight months, depending on the climate. When preparing for this long dormant period, the squirrel constructs a specific chamber called a hibernaculum. This specialized chamber maintains a consistent temperature and humidity, which is necessary for the animal to survive the winter with a drastically lowered metabolic rate.
The Alternative: Above-Ground Tree Nests
The more widely recognized tree squirrels, such as the Eastern Gray Squirrel, do not nest in the ground, instead constructing nests high in trees. The most common type of tree squirrel nest is called a drey, which is a spherical structure built from small twigs and leafy branches. The interior is lined with softer materials like grass, moss, and shredded bark for insulation and comfort.
These nests are strategically placed in the crotches of trees or close to the main trunk, often forty feet or more above the ground. Dreys serve primarily as shelter from weather and as a safe nursery for young, but they are generally less robust than a ground burrow. In colder months, tree squirrels often seek out natural tree cavities or hollow logs, which offer superior protection, as they remain active throughout the winter.
Identifying and Managing Ground Squirrel Activity
For homeowners, identifying ground squirrel activity involves looking for specific, tell-tale signs on the property. Burrows typically have entrances that are around three to four inches in diameter. Unlike the cone-shaped mounds created by gophers, ground squirrel entrances often have minimal or scattered piles of excavated dirt. Active burrows will usually look clean and well-maintained, sometimes with well-worn paths leading to them, as the animals are active during the day.
Management strategies for ground squirrels focus on making the environment less appealing and excluding the animals from vulnerable areas. Since ground squirrels prefer open areas for surveillance, removing debris piles and brush can make a property less desirable. Exclusion techniques, such as installing fencing made of hardware cloth, are effective if the barrier is buried at least twelve inches deep, preventing the squirrels from burrowing underneath.
Control measures are often most effective when timed to the squirrel’s life cycle. Trapping is most successful between February and October, when the animals are active and foraging. Fumigation of burrows is best performed in spring or when the soil is moist, as the dampness helps contain the gas within the tunnel system. Avoiding fumigation during the winter hibernation period is advised, as the squirrels often plug their burrows with soil, which can reduce the treatment’s effectiveness.