General: The Red Squirrel (Tamiasciurus hudsonicus) may be distinguished by its small size and its extreme territorial behavior, relative to other species of squirrels. Classified by the IUCN Red List as Least Concern, this widespread species is a common staple in ecosystems across North America. Spending its time hoarding massive amounts of cones and seeds for cold winter months, these squirrels are territorial of their nests and stockpiles and play an important role in seed distribution in their forest habitats.
Description: The Red Squirrel may be identified from other squirrels by their color, territorial behavior, and small size. Male and female squirrels are of a similar size and coloration, although regional variations can include color and size differences. The dorsal coloration can range from dark reddish brown, to brown or reddish-grey, contrasted by white or cream undersides. Unique markings include dark lateral lines on the body (which turn nearly black in the summer, separating the light underside from the dark upper,) white eye- rings, and tufted ears (evident during the winter.) The tail, flatter and 30% smaller than that of gray squirrels, may be yellowish-grey or deep red, with white or yellow tips on the hair and banded by black the length of the entire tail. Red Squirrels may weigh 197 to 282 grams, and be 6.5” to 9” long less than half the size of a fox squirrel. The tail makes up most of the body length, ranging from 3.5” to 6.5” in length. The Red Squirrel molts twice a year, once in the spring (between March and August, starting at the nose and ending at the posterior,) and once in the fall between August and December (starting at the tail and ending at the front legs)1. The tail of the Red Squirrel only molts in the fall. The body of the Red Squirrel is suited for climbing, with powerful rear legs and curved front claws used to grip bark.
In the wild, the Red Squirrel may live up to ten years; however, fewer than 25% of Red Squirrels live past the first year. The average lifespan of the Red Squirrel is three to seven years2 in the wild and five years in captivity.
The Red Squirrel has highly developed senses of smell, hearing and sight, making them well suited for foraging, climbing, and alluding predators.
Health: Red Squirrels are susceptible to a number of physical ailments, including parasites, fungal diseases, and viruses. Endoparasites (internal) include nematodes, tapeworms, tularemia bacteria, and sarocysts. Ectoparasties (external) include mites, ticks, fleas, and botfly larvae. They may develop a fungal lung disease infection by hosting adiaspiromycosis3. They are also prone to a number of viruses, including the silverwater virus, California encephalitis virus and Powassan virus4.
Behavior: Red Squirrels are a primarily diurnal species, most active during the early morning and in the late afternoon. During the fall red squirrels are generally more active in preparation of the winter.
During the winter, squirrels take advantage of mid-day temperature spikes, using this time to forage. These squirrels do not hibernate, despite common belief. Instead, they slow their activity levels according to temperatures. During the winter it is uncommon for a squirrel to stay inside a nest for more than one day without leaving to search for food. As temperatures dip below freezing, Red Squirrels become relatively inactive, taking refuge in a tree cavity, underground, or in a loosely constructed nest in a tree5.
The Red Squirrel is one of the most territorial squirrels of North America, using a variety of noises to defend their territory and food or fend off threats from predators. They are also very agile making them difficult to capture, but if cornered, they will defend themselves6. The Red Squirrel is known for its communication abilities, with noises ranging from rattles, chirps, screeches, and growls, to buzzes7. During mating season, males will use low aggressive, territorial calls to fend off other males. In response to threats, squirrels will give-off specific calls depending on the type of predator, a high frequency call for aerial attackers, or a sharp, bark for predators on the ground8.
In addition to vocal communication, Red Squirrels also use scent marking to aid in protection of territory or defense from predators, including snakes, birds of prey, and a variety of mammals9.
Habitat: Red Squirrels are primarily an arboreal species, inhabiting boreal coniferous, deciduous, or mixed northern forests. They may also reside in temperate or polar environments, in second-growth forests, suburban or urban areas, assuming coniferous trees are present with interlocking canopies and fungal resources10. Red Squirrels are found in a variety of ecosystems, with some populations living in mountainous regions up to 2500’. Territories, on average, are 2400 to 48000 square meters and are fiercely defended11.
Location: The Red Squirrel can be found across North America, with populations widely spread in Canada, Alaska, and parts of the United States, including the Rocky and Appalachian Mountains, and the Eastern United States as far south as northern Georgia12. 25 subspecies of the Red Squirrel have been identified. Isolated populations of the Red Squirrel include a subspecies in Arizona’s Pinaleño Mountains and an introduced population on the island of Newfoundland13.
Diet: Because the Red Squirrel inhabits areas with resource pulse systems (habitats with extreme seasonal variation in food supplies)14, they are opportunistic feeders who have been known to migrate in search of sustenance. These squirrels are primarily granivorous15, consuming a diet consisting mainly of conifer cones and seeds, and nuts. Their diets also include fruit, flowers, fungi, and buds, and when food supplies are low, will expand to include insects, bird eggs and hatchlings, and small vertebrates such as mice. Red Squirrels have also been observed feeding on sap, bark, and underlying tree tissue16.
Red Squirrels systematically harvest cones and seeds from pine trees and other conifers, collecting those with the highest energy density per cone first. The cones and seeds are cut from trees and stored in huge stockpiles, called middens. These food stores contain, on average, 2,000 to 4,000 cones and can be found in hollow stumps, at the bases of trees, underground, or under logs. Middens may contain upwards of 18,000 cones and be used by several generations of squirrels17. A typical sized midden holds enough food to last at least one or two seasons. Red Squirrels have also been known to use a process called scatter hoarding, hiding several small stockpiles of food rather than one large midden18. Because of their tendency to scatter food stores, Red Squirrels play an important part in seed distribution in their habitats.
Reproduction: Red Squirrels reach sexual maturity in one year and typically breed annually, following the cyclical production of conifer seeds and cones19. The breeding season lasts about 100 days, occurring in the spring. In warmer climates a second breeding season may occur in the late summer or early fall. Regional distribution causes variations in breeding times. For example, a second breeding season is common in the eastern United States, occurring in late July. Red Squirrels tend to be characterized as promiscuous in their mating but mating pairs do exist. Because of this behavior, an estrus female (in her period of ovulation) will be pursued by and mate with several males, participating in mating chases that can last up to several hours20. The dominant male will fend off the other males in the chase with physical displays of dominance or through audible communication. Estrus only lasts one day during the breeding season,21 and females will initiate copulation, which will occur several times during that afternoon. Gestation lasts, on average, 35 days. Litters may contain 1 to 8 offspring weighing just over 7 grams each22. The young are born naked and are weaned by 8 weeks old, although lactation occurs for 70 days23. By 18 weeks old the young are independent, moving away to establish their own territories. Sometimes, the mother will allot some or all of her territory to one or more of her young, moving away herself to establish a new territory. This act increases the success rate of her young.
Nests may be built in a number of locations, including tree hollows, cavities in the ground, in fallen logs or in tree limb junctions, although Red Squirrels prefer natural cavities. Nests are located within 100’ of food storage and are constructed of leaves, grass, moss, feathers, fur, or bark, depending on geographic location and available materials. When constructed in a tree, nests can be built from 6’ to 60’ off the ground.
Notes of Interest
Alternate names for the Red Squirrel include the North American Red Squirrel, Pine Squirrel, chickaree, and the Mount Graham Red Squirrel24.
The Mount Graham Red Squirrel is an isolated subspecies of the Red Squirrel consisting of one small population of approximately 250 squirrels. This subspecies was thought to be extinct in the 1950’s, but was rediscovered in the 1970’s25. This subspecies is endangered, according to the U.S. Fish and Wildlife Service.
The Red Squirrel faces a number of threats and certain populations and subspecies have experienced a decline in numbers due to harvesting for fur (the Red Squirrel is the third most harvested furbearer in Canada,) fragmentation of habitats due to forestry, construction of roads and civic development, forest fires, drought, and invasive species26.
Red Squirrels are a destructive species and may affect tree species as well as property. By stripping the bark and removing cones and buds from trees, these squirrels may inhibit the healthy growth of individual trees and tree populations. It has been determined that this species consumes 60% to 100% of cone crops in certain locations27. However, they also contribute to the distribution of seeds, leaving neglected stockpiles to germinate. Squirrels may also cause damage to property by nesting in homes or gnawing on items.
Red Squirrels have been known to bite humans when provoked28.