Squirrels: The Animal Answer Guide

5 Squirrel Ecology

Where do squirrels sleep? As we mentioned in the first chapter, squirrels live in an extraordinarily diverse range of habitats, from rain forests to deserts and valleys to high mountains. Within these habitats, all squirrels require a safe place to sleep, to give birth to and raise young, and to take shelter from inclement weather and predators. For many tree squirrels such a place is a nest in a tree or in a hollow of a tree. Leaf nests are usually built at least 4.5 meters (15 feet) up, in a solid location, such as the crook of a branch or against the trunk. Squirrels take the architecture of their nests seriously, using twigs, damp leaves, and moss compressed to create a solid base. They build up from there, creating supports with more twigs and filling in with leaves. These circular nests usually average 46 cm (1.5 feet) in diameter but necessarily are larger for larger species. Nests are lined with soft material, such as stripped bark, moss, fur, or even cotton batting from porch pillows. Leaf nests are quite sturdy, despite their outward appearance, and also are waterproof. Most tree squirrels have multiple nests within their home range—typically a well constructed one that is their primary nest and several other less sturdy ones that are used for midday resting or convenient escape from predators. Nests in tree hollows are the homes of choice for flying squirrels and for many tree squirrels if they are available. Tree hollows provide better protection from the elements than leaf nests and, when lined with soft material, are an ideal place to raise young. Some tree and flying squirrels will occasionally nest in unique locations. The woolly flying squirrel nests in caves, and there have been reports of the North American red squirrel nesting underground. Chapter 5 Squirrel Ecology 70 Squirrels: The Animal Answer Guide Most ground squirrels nest in burrows, though the structure and complexity of burrows varies widely across species. Black-tailed prairie dog burrows can be quite large and complex. Although they average 5–10 meters (16–33 feet) long and 2–3 meters (6.5–10 feet) deep, there are records of ones 33 meters (108 feet) long and 5 meters (16 feet) deep. Inside primary burrows are nest chambers, which are lined with grass and average around 30 cm (12 inches) high. These chambers are used for sleeping or for raising young. There are multiple entrances to burrows within a prairie dog coterie, and there are also different types of entrances. All five species of prairie dog create “dome-crater” entrances and entrances with no mound. The entrances with no mounds of dirt outside them are typically found on the edge of their territory and used to escape predators or take temporary shelter. Dome-crater entrances and their mounds are found more centrally and lead to primary burrows. These mounds are used as lookout points, to help prevent the flooding of the burrow by encouraging rainwater runoff and to help promote ventilation. The black-tailed prairie dog and the Mexican prairie dog both create an additional entrance type, called a rim crater, which resembles a small volcano and plays the same role as the dome crater. The antelope ground squirrel has many burrows distributed across its home range. Females do use a nest burrow, in which they raise young, but otherwise, these squirrels are not selective and will sleep in different burrows on different nights. Because the antelope ground squirrel lives in the desert, these multiple burrows offer convenient shelter during the heat of the day. Idaho ground squirrels have three different burrows: hibernation burrows, nest burrows, and auxiliary burrows. Nest burrows are rather complicated, containing up to thirteen tunnels, eleven openings, and seven chambers. Nests are usually located at the deepest part of the burrow. On the other hand, hibernation burrows consist of a single, steep tunnel ending in a nest chamber. Auxiliary burrows are simple, shallow burrows used primarily for shelter while foraging. Some ground squirrel burrows, such as those of Belding’s ground squirrels, are used for only a season, whereas other burrows, like those of the black-tailed prairie dog, can persist for many generations. The eastern chipmunk (Tamias striatus) has burrows that range from simple tunnels to complex systems involving many separate chambers, some for food storage, others for debris, and one for a nest chamber. They may be up to 10 meters (33 feet) in length. The burrows of the...