American Red Squirrel

American Red Squirrel
Conservation status
Least Concern (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Family:	Sciuridae
Genus:	Tamiasciurus
Species:	T. hudsonicus
Binomial name
Tamiasciurus hudsonicus (Erxleben, 1777)

The American Red Squirrel (Tamiasciurus hudsonicus) is one of two species of tree squirrel currently classified in the genus Tamiasciurus and known as pine squirrels (the other is the Douglas Squirrel T. douglasii). It is a medium sized (200–250 g) diurnal mammal that defends a year-round exclusive territory. The diet of these tree squirrels is specialized on the seeds of conifer cones. As such, they are widely distributed across North America wherever conifers are common, except on the Pacific coasts where they are replaced by Douglas Squirrels. Recently American Red Squirrel have been expanding their range to include primarily hardwood areas.^[2]

Binomial Nomenclature and identification

Front view, Gatineau Park, Quebec

American Red Squirrels are also referred to as Pine Squirrels, North American Red Squirrels and Chickarees. They should not be confused with Eurasian Red Squirrels (Sciurus vulgaris); since the ranges of these species do not overlap, they are both commonly referred to as "red squirrels" in the areas where they are native. The specific epithet hudsonicus refers to Hudson Bay, Canada, where the species was first catalogued by Erxleben in 1771.^[3] Red squirrels can be easily identified from other North American tree squirrels by their smaller size, territorial behavior and reddish fur with a white venter (under-belly).^[4] Red squirrels are also somewhat larger than chipmunks. The Douglas Squirrel is morphologically similar to the American Red Squirrels but has a rust venter and is restricted to the southwestern coast of British Columbia and in the Pacific Northwest of the United States. These two species do not co-occur.

Evolution/Systematics

American Red Squirrels are widely distributed across North America. Their range includes most of Canada, and extends into the United States in the Rocky Mountains, the North Central and North East. There are 25 recognized sub-species of red squirrels.^[4] The sub-species of red squirrel found in the southwest Yukon is T. hudsonicus petulans.^[4][5] A recent phylogeny^[6] suggests that squirrels as a family can be divided into five major lineages. Two of these clades are monotypic. Red squirrels (Tamiasciurus) fall within one of three remaining clades that includes flying squirrels and other tree squirrels (e.g., Sciurus). This clade is thought to have diverged from ground squirrels, chipmunks and marmots. See Mercer and Roth^[6] for details and interesting discussion of the climatic and tectonic events associated with these diversifications.

Status

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 endangered.^{[citation needed]}

Food habits

Eating nut

American Red Squirrels are primarily granivores, but incorporate other food items into their diet opportunistically.^[4] In the Yukon, extensive behavioral observations suggest that white spruce seeds (Picea glauca) comprise over 50% of a red squirrel’s diet (McAdam & Boutin unpub. data), but squirrels have also been observed eating the following: spruce buds and needles, mushrooms, willow (Salix sp.) leaves, poplar (Populus sp.) buds and catkins, bearberry (Arctostaphylos sp.) flowers and berries, and animal material such as bird eggs.^[7] White spruce cones mature in late July and are harvested by red squirrels in August and September. These harvested cones are stored in a central cache and provide energy and nutrients for survival over the winter and reproduction the following spring. The fallen scales from consumed seed cones can collect in piles, called middens, more than a meter across. White spruce exhibits 2–6 year masting cycles, where a year of superabundant cone production (mast year)^[8] is followed by several years in which few cones are produced.^[9] American Red Squirrel territories may contain only one or several middens.

Red squirrels clip and gather truffles/mushrooms and place them amongst the branches of trees to dry them in the sun.^[10][11][12]

Nesting behavior

Nests are most commonly constructed of grass in the branches of spruce trees. Nests are also excavated from witches’ broom—abnormally dense vegetative growth resulting from a rust disease—or cavities in the trunks of spruce, poplar trees, and walnut. Kluane red squirrels rarely nest below ground. Each individual squirrel has several nests within its territory and females with young move offspring between nests. Some behavior has been reported within human dwellings using insulation as nesting fodder.^{[citation needed]}

Reproduction

American Red Squirrels are spontaneous ovulators.^[13][14] Females enter estrus for only one day, but venture from their territory prior to ovulation and these exploratory forays may serve to advertise their upcoming estrus. On the day of estrus, females are chased by several males in an extended mating chase. Males compete with one another for the opportunity to mate with the estrous female. Estrous females will mate with 4–16 males. Gestation has been reported to range from 31 to 35 days.^[15] Females can breed for the first time at one year of age but some females delay breeding until two years of age or older. Most females produce only one litter, but in some years reproduction is skipped while in other years some females attempted to breed twice. Litter sizes typically range from 1 to 5, but most litters contain 3 or 4 offspring. Offspring are pink and hairless at birth and weigh approximately 10 g. Offspring grow at approximately 1.8 g/day while nursing but do not reach adult body size until 125 days of age. Offspring first emerge from their natal nest at around 42 days of age but continue to nurse until approximately 70 days.

In the June 2008 issue of Animal Behavior, researchers, studying a population of red squirrels over a period of three years in southwest Yukon, reported that female red squirrels showed high levels of multi-male mating and would even mate with males that had similar genetic relatedness, basically mating with their relatives. While males mating with multiple females is quite common in the animal kingdom, females that multi-mate is much harder to explain. Through their observations, it was noted that when female red squirrels chose a mate to copulate with, genetic relatedness did not play a factor. The researchers also found that the relatedness of parents had no effect on the neonatal mass and growth rate of their offspring, nor did it affect the survival rate of offspring to one year of age.^[16]

Dispersal

Juvenile American Red Squirrels must acquire a territory and midden prior to their first winter. Juveniles without a midden do not survive their first winter. Offspring can acquire a territory by competing for a vacant territory, creating a new territory or by receiving all or part of a territory from their mother. This somewhat rare (15% of litters) female behavior is referred to as breeding dispersal or bequeathal and is a form of maternal investment in offspring.^[17] The prevalence of this behavior is related to the abundance of food resources and the age of the mother. In some cases females will acquire additional middens prior to reproduction, which they later bequeath to their offspring.^[18] Offspring that do not receive a midden from their mother typically settle within 150 m (3 territory diameters) from their natal territory.^[17]

Survival

American Red Squirrels experience severe early mortality (on average only 22% survive to one year of age). The survival probability, however, increases to age three at which point it begins to decrease again. Females that survive to one year of age have a life expectancy of 2.3 years and a maximum lifespan of eight years.

Predators

American Red Squirrels are preyed upon by Canadian Lynx (Lynx canadensis), Bobcat (Lynx rufus), Coyote (Canis latrans), Great Horned Owl (Bubo virginianus), Northern Goshawk (Accipiter gentilis), Red-tailed Hawk (Buteo jamaicensis), American Crow (Corvus brachyrynchos), American Marten (Martes americana), Red Fox (Vulpes vulpes), Gray Fox (Urocyon cinereoargenteus), Wolf (Canis lupus) and weasel (Mustela sp.). However, predation on adult American Red Squirrels is thought to be relatively low compared to other mammals living in the North (e.g., snowshoe hares).

Other

The American Red Squirrel has been found in a black phase and recently, a white phase (not albino) in Alaska.^{[citation needed]}

References

External links

Wikimedia Commons has media related to: American Red Squirrel

Wikispecies has information related to: American Red Squirrel

• Tamiasciurus hudsonicus (TSN 180166). Integrated Taxonomic Information System. Retrieved on 18 March 2006.
• Kluane Red Squirrel Project web page, Accessed on September 6, 2006.
• Smithsonian article on American Red Squirrel