American Red Squirrel

Tamiasciurus hudsonicus

Description

Red squirrels differ from other tree squirrels by their deep reddish color, territorial behavior, and their smaller body size. They are less than 30% the size of grey squirrels (Sciurus carolinensis). While size and pelage color can vary geographically, they generally have a reddish back and white underside that is demarcated by dark lateral lines, which are especially visible in summer. A white eye ring is present year-round and tufted ears are during the winter. Variation in the dorsal surface color can range from reddish to ferruginous brown to olivaceous gray, usually with a distinctive reddish or brownish lateral band running down the back. The tail is smaller and flatter than that of other tree squirrels and varies in color from yellowish-gray to rusty red, with a band of black often extending the entire length of tail. Where its range borders that of Douglas squirrels (Tamiasciurus douglasii), red squirrels are distinguished by color of their pelage. The underside of red squirrels is all white or cream, whereas Douglas squirrels are rust colored or with a blackish wash. Tail hairs have yellowish to rusty tips with a black band in red squirrels, whereas those ofDouglas squirrels are white-tipped with a black band, making them moderately easy to distinguish from a distance. Male and female red squirrels are very similar in appearance.

Behavior

Red squirrels are primarily diurnal, but on occasion exhibit nocturnal activity. During the spring and summer they are most active in the morning and afternoon, but as fall approaches they become highly active all day in preparation for the food shortages associated with winter. In the winter, red squirrels peak their activity around midday to take advantage of warmer temperatures. Adverse weather may result in reduced activity, but it is unlikely that squirrels will remain in the nest for more than 1 day without foraging. As the temperatures drop, squirrels become less active, and it has been reported that at temperatures of -31.6 degrees Celsius, red squirrels become completely inactive. This likely varies geographically because squirrels living in Fairbanks, Alaska would have to be actively foraging at these temperatures or they would be confined to their nest for weeks.

Throughout most of their range, and especially in coniferous forests, both male and female squirrels vigorously defend exclusive territories from competitors. Defense of these territories occurs year-round but is most obvious in autumn when squirrels are stockpiling cones and when competition from subordinate squirrels is at its peak. In New York forests, which are dominated by deciduous trees, squirrels often exhibit overlapping home ranges and occasionally defend only nests and caches from intruders. Their territories range from 2400 to 48000 square meters.

Habitat

Red squirrels occupy northern boreal coniferous forests abundant with conifer seeds, fungi, and interlocking canopies. This limits them to mountain ranges on the southern and eastern boundaries of their range. In the Rocky Mountains they have been found at elevations up to 2,500 ft (762 m). Populations of red squirrels occur in different habit conditions due to the vastness of their range. They occur in both temperate and polar environments and are considered to be primarily arboreal. They can be found in a mixed variety of forests including coniferous, deciduous, and mixed forests and they are also able to thrive in suburban and urban settings, as long as cool, coniferous forests with dense, interlocking canopies and abundant fungal resources are present.

Distribution

American red squirrels are widely distributed across North America. Their range includes most of Canada and east of the Rocky Mountains in the United States. American red squirrels are abundant and not of conservation concern throughout much of their range. However, an isolated population of red squirrels in Arizona has experienced considerable declines in population size. In 1987, this portion of the population was listed as an endangered species.

Reproduction

Red squirrels have a defined breeding season lasting 105 days that can occur either once or twice a year. They will mate in early spring from March to May and then again in August to early September. A second breeding period tends to occur in warmer areas of their range. Although mate pairings may occur, red squirrels are generally characterized as promiscuous. Animals in the best condition tend to breed more regularly and successfully than animals in poor condition. Red squirrels exhibit a scramble competition mating system, in which the main costs to males are locating receptive females. Males typically invade the territory of females in estrus and pursue them in obvious mate chases. During mate chasing, a single dominant male actively pursues a female and drives off other subordinate males using calls or direct chase.

Food Habits

Red squirrels are primarily granivorous, but they are also opportunistic omnivores in the absence of mast foods. Primary diet items vary with habitat and include the seeds of conifers and other tree types detailed below. They live in a resource pulse system, where foods (conifers like white spruce, Picea glauca) exhibit extreme annual variation. They consume a wide variety of mushrooms, including at least 45 species in the Cascade Mountains alone. Secondary food items include tree buds and flowers, fleshy fruits, tree sap, bark, insects, and other animal materials such as bird eggs or young snowshoe hares (Lepus americanus). During winter, spring, and early summer, bark stripping and tree girdling occurs commonly to access phloem and cambial tissues. Red squirrels are highly selective in their foraging behavior, harvesting cones from the tree species with the highest seed energy per cone first and systematically working their way through species of conifers by energy density per cone.

Red squirrels are primarily larder hoarders. In late summer through autumn, they harvest cones and store them in one or a few central middens. Middens are a central hoard that is easy to defend from competitors and provides a moist, cool environment that prevents cones from opening. Middens vary in size and number depending on habitat, food availability, and individual squirrel. However, they contain enough food to last one to two seasons and are often used by several generations of squirrels In the eastern United States and Canada, red squirrels frequently engage in scatter hoarding, which is a system involving many small hoards instead of a large midden. This accounts for 85% of all hoards and more than 50% of all cones stored in this area The downside to this type of storage is that middens only provides enough food for about 37 days. Red squirrels have a great sense of smell which they use when looking for middens during the winter. Some individuals store their food caches underground and are able to locate these seeds, even under 4 meters of snow. Whenever they do not recover a stockpile of food, the seeds are left to germinate.

Ecosystem Roles

Red squirrels impact the forest ecosystem by dispersing seeds and fungi through caching and forgetting about or otherwise failing to return to food caches. The diversity and abundance of beneficial ectomycorrhizal fungi in these caches helps young trees acquire nutrients and grow. They limit the regrowth of trees by eating the seeds and inner tissues of the trees, which can cause significant damage to tree survival and value. Red squirrels provide a feeding opportunity for porcupines (Erethizontidae) during the winter by peeling away the bark of lodgepole pines. Their feeding habits also cause conifers to grow multiple tops, which reduces their timber value but increases suitable nest sites for many arboreal rodents (Rodentia) and passerine birds (Passeriformes). The increased availability of nest sites sustains species richness.

Red squirrels are host to a variety of endoparasites and ectoparasites. Endoparasitic species include 9 species of nematodes, 9 species of tapeworms including the genus (Hymenolepis). Other endoparasites include tularemia bacteria (Francisella tularensis) and Emmonsia crescens), and some kinds of protists like sarocysts (Sarocystis), and (Haplosporanigium). They are also vulnerable to fungal lung disease infection via adiaspiromycosis (Emmonsia parva). Ectoparasites of red squirrels include 31 species of mites, ticks, and chiggers (Glycyphagidae and Acarina), 25 species of fleas including Siphonaptera, Opisodasys robustus, Orchopeas caedens, Orchopeas neotomae, Orchopeas leucopus, Oropsylla idahoensis, Ceratophyllus vison. They may also carry botfly larvae (Cuterebra emasculator). Viruses that infect red squirrels are silverwater virus, California encephalitis virus, and Powassan virus.