American red squirrel

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American red squirrel
Tamiasciurus hudsonicus CT.jpg
At Cap Tourmente National Wildlife Area, Quebec
Status TNC G5.svg
Secure  (NatureServe) [2]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Sciuridae
Genus: Tamiasciurus
Species:
T. hudsonicus
Binomial name
Tamiasciurus hudsonicus
(Erxleben, 1777)
Subspecies [3]
  • T. h. hudsonicus
  • T. h. abieticola
  • T. h. baileyi
  • T. h. columbiensis
  • T. h. dakotensis
  • T. h. dixiensis
  • T. h. fremonti
  • T. h. gymnicus
  • T. h. kenaiensis
  • T. h. lanuginosus
  • T. h. laurentianus
  • T. h. loquax
  • T. h. lychnuchus
  • T. h. minnesota
  • T. h. pallescens
  • T. h. petulans
  • T. h. picatus
  • T. h. preblei
  • T. h. regalis
  • T. h. richardsoni
  • T. h. streatori
  • T. h. ungavensis
  • T. h. ventorum
Tamiasciurus hudsonicus range map.png
Distribution (including T. fremonti )

The American red squirrel (Tamiasciurus hudsonicus) is one of three species of tree squirrels currently classified in the genus Tamiasciurus , known as the pine squirrels (the others are the Douglas squirrel, T. douglasii, and the southwestern red squirrel, T. fremonti). The American red squirrel is variously known as the pine squirrel or piney squirrel, North American red squirrel, chickaree, boomer, or simply red squirrel. The squirrel is a small, 200–250 g (7.1–8.8 oz), diurnal mammal that defends a year-round exclusive territory. It feeds primarily on the seeds of conifer cones, and is widely distributed across much of the United States and Canada wherever conifers are common, except in the southwestern United States, where it is replaced by the formerly conspecific southwestern red squirrel, and along the Pacific coast of the United States, where its cousin the Douglas squirrel is found instead.

Contents

The squirrel has been expanding its range into hardwood forests. [4]

Taxonomy

American red squirrels 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 simply "red squirrel" 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; [5] accordingly, the species was formerly sometimes known as Hudson's Bay squirrel, such as in John James Audubon's work The Viviparous Quadrupeds of North America. A recent phylogeny suggests the squirrels as a family can be divided into five major lineages. Red squirrels (Tamiasciurus) fall within the clade that includes flying squirrels and other tree squirrels (e.g., Sciurus ). [6] There are 25 recognized subspecies of the American red squirrel. [7]

The southwestern red squirrel (T. fremonti) was long considered conspecific with T. hudsonicus, but a 2016 phylogenetic study found it to be a distinct species. [8]

Description

Red squirrels can be easily distinguished from other North American tree squirrels by their smaller size, 28–35 cm (11–14 in) total length (including tail), territorial behavior, and reddish fur with a white venter (underbelly). [7] Red squirrels are somewhat larger than chipmunks.

The Douglas squirrel is morphologically similar to the American red squirrels, but has a rust-colored venter and is restricted to the southwestern coast of British Columbia and in the Pacific Northwest of the United States. The ranges of the American red squirrel and the Douglas squirrel overlap in southern British Columbia, northwestern Washington and eastern Oregon. [9]

Distribution

Front view, Gatineau Park, Quebec Red squirrel.jpg
Front view, Gatineau Park, Quebec

American red squirrels are widely distributed across the North American continent. Their range includes: most of Canada, excluding northern areas with no tree cover, the southern half of Alberta and the southwestern coast of British Columbia; the southern half of Alaska; the Rocky Mountains area of the United States, and northern half of the eastern United States. [7] [10] American red squirrels are abundant and not of conservation concern throughout much of their range. American red squirrels were introduced on Newfoundland and have lived there in abundance for decades. [11] The endangered subspecies grahamensis , found only on Mt. Graham, Arizona, was formerly considered a member of this species, but is now considered a subspecies of the southwestern red squirrel Tamiasciurus fremonti. [8] [12]

Fresh Red Squirrel tracks in snow. Red Squirrel Tracks in Snow.jpg
Fresh Red Squirrel tracks in snow.

Behavior

Feeding

Eating nut, in Edmonton, Alberta American squirrel eating nut, 13 Jun 2013.JPG
Eating nut, in Edmonton, Alberta
Video of a red squirrel eating, in Quebec
Large midden constructed by American red squirrels, Kenai National Wildlife Refuge, Alaska Red squirrel midden.jpg
Large midden constructed by American red squirrels, Kenai National Wildlife Refuge, Alaska

American red squirrels are primarily granivores, but incorporate other food items into their diets opportunistically. [7] In The Yukon, extensive behavioral observations suggest white spruce seeds (Picea glauca) comprise more than 50% of a red squirrel's diet, but squirrels have also been observed eating 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 or even snowshoe hare leverets (young). [13] 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, up to twelve meters across. [14] White spruce exhibits two- to six-year masting cycles, where a year of superabundant cone production (mast year) [15] is followed by several years in which few cones are produced. [16] American red squirrel territories may contain one or several middens.

American red squirrels eat a variety of mushroom species, including some that are deadly to humans. [17]

Reproduction

American red squirrels are spontaneous ovulators. [18] [19] 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 to 16 males. Gestation has been reported to range from 31 to 35 days. [20] 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 one to five, but most litters contain three or four offspring. Offspring are pink and hairless at birth and weigh about 10 g. Offspring grow at approximately 1.8 g per day while nursing, and reach adult body size at 125 days. They first emerge from their natal nests 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. American red squirrels rarely nest below ground. Each individual squirrel has several nests within its territory, and females with young move them between nests. Some behavior has been reported within human dwellings using insulation as nest material.

A three-year study of a population of red squirrels in southwest Yukon reported female red squirrels showed high levels of multiple-male mating and would even mate with males with similar genetic relatedness. 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. [21]

Sociality

Red squirrels are highly territorial and asocial with very few non-reproductive physical interactions (0.6% of all recorded behaviours in one 19-year study). [22] The majority of physical interactions are in male-female matings and between females and their offspring before the offspring disperse to their own territories (see Dispersal and survival). The non-reproductive physical interactions recorded were all instances of chasing an intruder from a territory. [22]

Dispersal and survival

Red squirrel swimming Swimming red squirrel.jpg
Red squirrel swimming

If juvenile American red squirrels are to survive their first winter, they must acquire a territory and midden. They 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 mothers. 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. [23] 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. [24] Offspring that do not receive a midden from their mother typically settle within 150 m (3 territory diameters) of their natal territory. [23] Observations suggest that male red squirrels have environmentally induced, alternative reproductive strategies that result in higher incidences of sexually selected infanticide in years when food is plentiful. [25]

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, when it begins to decrease again. Females that survive to one year of age have a life expectancy of 3.5 years and a maximum lifespan of 8 years. [26] Increased maternal attention is correlated with increased offspring growth rate and higher lifetime reproductive success. [27]

Chief predators include Canada 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), pacific marten (Martes caurina), red fox (Vulpes vulpes), gray fox (Urocyon cinereoargenteus), wolf (Canis lupus), and weasel (Mustela sp.). [28]

Related Research Articles

<span class="mw-page-title-main">Behavioral ecology</span> Study of the evolutionary basis for animal behavior due to ecological pressures

Behavioral ecology, also spelled behavioural ecology, is the study of the evolutionary basis for animal behavior due to ecological pressures. Behavioral ecology emerged from ethology after Niko Tinbergen outlined four questions to address when studying animal behaviors: What are the proximate causes, ontogeny, survival value, and phylogeny of a behavior?

<span class="mw-page-title-main">American coot</span> Species of bird

The American coot, also known as a mud hen or pouldeau, is a bird of the family Rallidae. Though commonly mistaken for ducks, American coots are only distantly related to ducks, belonging to a separate order. Unlike the webbed feet of ducks, coots have broad, lobed scales on their lower legs and toes that fold back with each step to facilitate walking on dry land. Coots live near water, typically inhabiting wetlands and open water bodies in North America. Groups of coots are called covers or rafts. The oldest known coot lived to be 22 years old.

<span class="mw-page-title-main">European pied flycatcher</span> Species of bird

The European pied flycatcher is a small passerine bird in the Old World flycatcher family. One of the four species of Western Palearctic black-and-white flycatchers, it hybridizes to a limited extent with the collared flycatcher. It breeds in most of Europe and across the Western Palearctic. It is migratory, wintering mainly in tropical Africa. It usually builds its nests in holes on oak trees. This species practices polygyny, usually bigamy, with the male travelling large distances to acquire a second mate. The male will mate with the secondary female and then return to the primary female in order to help with aspects of child rearing, such as feeding.

<span class="mw-page-title-main">Canada jay</span> Passerine bird of the family Corvidae

The Canada jay, also known as the gray jay, grey jay, camp robber, or whisky jack, is a passerine bird of the family Corvidae. It is found in boreal forests of North America north to the tree line, and in the Rocky Mountains subalpine zone south to New Mexico and Arizona. A fairly large songbird, the Canada jay has pale grey underparts, darker grey upperparts, and a grey-white head with a darker grey nape. It is one of three members of the genus Perisoreus, a genus more closely related to the magpie genus Cyanopica than to other birds known as jays. The Canada jay itself has nine recognized subspecies.

<span class="mw-page-title-main">Pine squirrel</span> Genus of rodents

Pine squirrels are squirrels of the genus Tamiasciurus, in the Sciurini tribe, of the large family Sciuridae.

<span class="mw-page-title-main">Eastern gray squirrel</span> Tree squirrel native to eastern and central North America

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<span class="mw-page-title-main">Blue-headed vireo</span> Species of bird

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<span class="mw-page-title-main">Boreal chickadee</span> Species of bird

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<span class="mw-page-title-main">Red squirrel</span> Species of tree squirrel common in Europe and Asia

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<span class="mw-page-title-main">Douglas squirrel</span> Species of rodent

The Douglas squirrel is a pine squirrel found in western North America, from the Pacific Northwest to central California, with an isolated subspecies in northern Baja California, Mexico. It is sometimes known as the chickaree or pine squirrel, although these names are also used for the American red squirrel. Variant spellings of the common name are Douglas' squirrel and Douglas's squirrel. The Native Americans of Kings River called it the "Pillillooeet", in imitation of its characteristic alarm call.

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<span class="mw-page-title-main">Abert's squirrel</span> Species of rodent

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<span class="mw-page-title-main">Belding's ground squirrel</span> Species of rodent

Belding's ground squirrel, also called pot gut, sage rat or picket-pin, is a squirrel that lives on mountains in the western United States. In California, it often is found at 6,500 to 11,800 feet (2,000–3,600 m) in meadows between Lake Tahoe and Kings Canyon. This species is not of conservation concern, and its range includes some protected areas.

<span class="mw-page-title-main">Infanticide (zoology)</span> Killing of young offspring by an adult animal of the same species

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<span class="mw-page-title-main">Arizona gray squirrel</span> Species of rodent

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<span class="mw-page-title-main">Mearns's squirrel</span> Subspecies of rodent

Mearns's squirrel is a subspecies of the Douglas squirrel endemic to Mexico. It is endangered and occurs in low densities, and is threatened by habitat loss. It is possibly also threatened by competition from the eastern gray squirrel, which was introduced to the range of Mearns's squirrel in 1946, but may not be present anymore. It is closely related to other subspecies of the Douglas squirrel, but far less is known about its behavior, which was first studied in detail in 2004. It is named for the 19th-century American naturalist Edgar Mearns.

<span class="mw-page-title-main">Mount Graham red squirrel</span> Subspecies of rodent

The Mount Graham red squirrel is an endangered subspecies of the southwestern red squirrel native to the Pinaleño Mountains of Arizona. It is smaller than most other subspecies of red squirrel, and also does not have the white-fringed tail that is common to the species. Its diet consists mainly of mixed seeds, conifer cones and air-dried fungi. It exhibits similar behavior to other squirrels in its species.

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<span class="mw-page-title-main">Southwestern red squirrel</span> Species of tree squirrel

The southwestern red squirrel or Fremont's squirrel is a species of tree squirrel endemic to high-altitude regions of the southwestern United States.

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