AppearanceRed squirrels can be easily identified from other North American tree squirrels by their smaller size, territorial behavior and reddish fur with a white venter . Red squirrels are 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 species' ranges do not overlap.
DistributionAmerican 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 endangered.
ReproductionAmerican red squirrels are spontaneous ovulators. 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. 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 one litter per year, but in some years reproduction is skipped while in other years some females 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 and reach adult body size at 125 days. Offspring first emerge from their natal nest at around 42 days but continue to nurse until approximately 70 days.
Nests are most commonly constructed of grass in the branches of 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, and walnut trees. 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.
A three-year study of a population of red squirrels 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. While males mating with multiple females is quite common in the animal kingdom, females that multi-mate is rarer. 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.
FoodAmerican red squirrels are primarily granivores, but incorporate other food items into their diet opportunistically. In the Yukon, extensive behavioral observations suggest that white spruce seeds comprise over 50% of a red squirrel's diet, but squirrels have also been observed eating spruce buds and needles, mushrooms, willow leaves, poplar buds and catkins, bearberry flowers and berries, and animal material such as bird eggs or even snowshoe hare leverets . 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 is followed by several years in which few cones are produced. American red squirrel territories may contain one or several middens.
Red squirrels clip and gather truffles and other fungi and place them amongst the branches of trees to dry them in the sun.
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