Squirrels of North America
The golden-mantled ground squirrel (Callospermophilus lateralis), which is found in the western half of the U.S. and in the Canadian Rocky Mountains, is certainly one of the most beautiful squirrel species in the world. – This one is sitting on a log in Yosemite National Park, California. (Photo copyright © by Kaj Halberg)
In 1803, U.S. President Jefferson ordered two officers, Colonel Meriwether Lewis and Captain William Clark, to undertake an expedition across the North American West. The purpose of this journey was to describe the area, which was unknown to the white man, and to possibly find an easy access to the American West Coast.
During their three-year long expedition, Lewis and Clark sent various items to President Jefferson in Washington. Among these was a parcel, containing a small animal which they had encountered on the prairie. They found that the warning call of this animal sounded like a dog, so they labelled the parcel, “Wild dog of the prairie.”
The black-tailed prairie dog (Cynomys ludovicianus) is the most numerous of the five species of prairie dog. This picture is from Badlands National Park, South Dakota. (Photo copyright © by Kaj Halberg)
Young black-tailed prairie dog, grooming its mother, Devil’s Tower National Monument, Wyoming. (Photo copyright © by Kaj Halberg)
Dog mouse of the prairie
Prairie dogs are not at all dogs, but a type of ground squirrel. Their warning call is indeed slightly reminiscent of a barking dog, and when they sit on their haunches outside their den, keeping a lookout for enemies, they do look a bit like a little, fat dog. Their generic name, Cynomys, means ‘dog mouse’ in the Greek.
There are five species of prairie dog, of which the most common is black-tailed (Cynomys ludovicianus), which, like Mexican (C. mexicanus), has a black tip to the tail. Three other species, white-tailed (C. leucurus), Utah (C. parvidens), and Gunnison’s (C. gunnisoni), all have white tip to the tail. The Utah prairie dog lives at higher altitudes than the other species, at 1,500 to 2,700 metres altitude, hibernating about six months of the year. The other species do not hibernate, but during harsh winter weather, they undergo a mild stupor for a few days at a time.
Prairie dogs live in large underground colonies on the prairie, popularly called ‘prairie dog towns’. Each family has several entrances to their ‘apartment’. These entrances are at different levels, causing an air current to flow through the tunnels, which will supply fresh oxygen to the animals.
Their diet consists of grasses and various herbs, and each animal consumes more than twice its own weight every month. They also eat insects and other invertebrates, and research has revealed that no less than 39% of young prairie dogs fall victim to cannibalism.
Prairie dog droppings deliver nutrients for a number of plant species to grow, and many larger herbivores benefit from this, e.g. the American bison (Bos bison) and the pronghorn (Antilocapra americana). Carnivores like bobcat (Lynx rufus), coyote (Canis latrans), American badger (Taxidea taxus), and kit fox (Vulpes macrotis), and birds like eagles, prairie falcon (Falco mexicanus), and ferruginous hawk (Buteo regalis) feed on prairie dogs. One species, the burrowing owl (Athene cunicularia), depends on the squirrels for nesting holes. In this way, prairie dogs create a unique ecosystem.
The black-footed ferret (Mustela nigripes) is a mustelid, which used to be common in prairie dog towns, feeding on the squirrels in their underground tunnels. By 1970, it was feared that this interesting animal had become extinct. However, a small population was found in Wyoming in 1981, and since then, through captive breeding, its numbers have increased tremendously. It has been released in the wild at a number of locations, and seems to thrive, so it may still be possible to save this unique animal.
Sitting on its haunches outside its burrow in Badlands National Park, South Dakota, keeping a lookout for enemies, this black-tailed prairie dog does indeed look a bit like a little fat dog. (Photo copyright © by Kaj Halberg)
Female black-tailed prairie dog with young outside their den, Tucson Desert Zoo, Arizona. Research has revealed that no less than 39% of young prairie dogs fall victim to cannibalism. (Photos copyright © by Kaj Halberg)
Declining populations of prairie dogs
Formerly, prairie dogs were unbelievably numerous. Towards the end of the 19th Century, a population of five billion was estimated, the largest prairie dog towns covering tens of thousands of square kilometres. Following the arrival of European settlers, most of the prairie was cultivated, or utilized for grazing, and prairie dogs were regarded as a pest, as they would undermine the fields, eat the crops, and compete with cattle for fodder. Farmers began a large-scale eradication of prairie dogs, using diverse methods like poison, dynamite, drowning, shooting, gassing, and spreading of contagious diseases.
A hundred years later, prairie dog numbers were down by more than 90%, and today only scattered populations exist. By far the largest colony is in the Janos Region of Chihuahua State in Mexico, where hundreds of thousands of black-tailed prairie dogs survive, although their numbers are declining, mainly due to increasing cultivation of the area.
Today, the Utah prairie dog is restricted to an area of about 1,850 square kilometres in southern Utah. The total population may be less than 8,000, and despite being strictly protected, its numbers are still declining. The Mexican prairie dog is endemic to north-central Mexico, only found in the states of Coahuila and San Luis Potosi, formerly also occurring in the states of Nuevo Leon and Zacatecas. The present number of this species is unknown, but its total area of distribution is less than 600 square kilometres. Both of these species are threatened with extinction. The populations of the white-tailed and Gunnison’s prairie dogs are declining, and both species are regarded as vulnerable.
Its snout and paws muddy from spring cleaning, this Utah prairie dog (Cynomys parvidens) is sitting outside its burrow in Bryce Canyon National Park, Utah. (Photo copyright © by Kaj Halberg)
Squirrels are a large family of rodents, numbering about 300 species worldwide, and found on all continents, except Australia and Antarctica. Most species live in tropical rainforests. Temperate Eurasia only harbours about 20 species, whereas the family is very diverse in North America, numbering altogether c. 84 species, belonging to seven distinct groups.
The scientific family name of squirrels, Sciuridae, is derived from Sciurus, the name given in 1758 to the Eurasian red squirrel by Swedish naturalist Carolus Linnaeus (1707-1778), also called Carl von Linné. Sciurus is a Latinized form of the Greek word skiouros, meaning ‘shadow-tailed’, from skia (‘shadow’) and oura (‘tail’), referring to the large, bushy tail of many squirrels. Some species have a habit of flicking their tail over their back, and in this way tropical species are able to use their tail as a protection against the fierce sunshine.
Squirrels are mainly vegetarians, but also eat various insects and other invertebrates, besides eggs and young of smaller birds. Larger squirrels are able to kill small mammals like mice, and a Mexican ground squirrel (Ictidomys mexicanus) was observed killing a young rabbit, which was almost a fourth of its own size. Cannibalism occurs in several species. Sometimes squirrels feed on dead animals.
Many of the North American species hibernate during winter, and some even aestivate during the hottest part of the summer. At higher altitudes, male Belding’s ground squirrels (Urocitellus beldingi) may hibernate as much as eight months a year. They emerge when snow is still covering the ground, looking for mates. After mating, they feed voraciously, so that their weight may be doubled, before they again start hibernating by late August. Larger males may even kill newly emerged young squirrels and feed on them.
Dead squirrels should be handled with care, as their fleas can carry bubonic plague.
Belding’s ground squirrel (Urocitellus beldingi), standing outside its den, Carson Pass, California. This species may hibernate as much as eight months a year. (Photo copyright © by Kaj Halberg)
In North America, 16 species of bushy-tailed tree squirrels are found, of which the eastern grey squirrel (Sciurus carolinensis) is the most widespread, found in the eastern half of the continent, and introduced to several areas in the West. It is very common in towns, as long as there are trees, where it can take shelter from dogs and other enemies. Grey squirrels are active throughout the year, and in autumn they store nuts and fruits in underground caches. They are not able to remember where the food was buried, but find it by smelling it under the snow. Grey squirrels are often a nuisance on bird feeders, where they consume most of the food, intended for birds. In parks and other places, where people regularly feed grey squirrels, they become very tame indeed.
The eastern grey squirrel has been successfully introduced to South Africa, Britain, and other places. In Britain, it is regarded as a pest, as it outcompetes the native European red squirrel (Sciurus vulgaris), which is now scarce south of Scotland. Extermination campaigns of grey squirrels have now been initiated in the U.K., causing the red squirrel to increase several places.
Eastern grey squirrel, Kew Botanical Gardens, London. (Photo copyright © by Kaj Halberg)
Eastern grey squirrels are often a nuisance on bird feeders, where they consume most of the food, as in this picture from Long Island, New York. (Photo copyright © by Kaj Halberg)
Where people regularly feed grey squirrels, they become very tame indeed, as this one in Kew Botanical Gardens, London. (Photo copyright © by Kaj Halberg)
The western grey squirrel (Sciurus griseus) has a larger and bushier tail than its eastern counterpart. It is distributed in the Pacific States, from northern Washington to southern California, just entering northern Baja California, Mexico.
Western grey squirrel, Yosemite National Park, California. (Photo copyright © by Kaj Halberg)
The fox squirrel (Sciurus niger) is distributed all over eastern U.S. and south-eastern Canada, west to the Dakotas, Colorado, and Texas. The colour of this species varies tremendously, western populations being mostly yellowish-brown, while eastern populations are darker, from dark brown to almost black.
Some individuals of eastern populations of the fox squirrel are almost black, like this one, resting on a branch in Carolina Beach State Park, North Carolina. (Photo copyright © by Kaj Halberg)
Interestingly, the Grand Canyon seems to constitute a barrier between two subspecies of bushy-tailed squirrels, found on the Colorado Plateau. They are of similar size, with large bushy tails and long ear tufts – but their colouring is very different. Abert’s squirrel (Sciurus aberti ssp. aberti), which lives in coniferous forests south of the Grand Canyon, has white belly and grey tail, whereas the Kaibab squirrel (S. aberti ssp. kaibabensis), which is found in a similar habitat north of the canyon, has black belly and white tail.
Other bushy-tailed squirrels include the American red squirrel (Tamiasciurus hudsonicus), which has a very wide distribution, from Alaska across most of Canada to the north-eastern U.S., the Appalachians, and the Rocky Mountains, and Douglas’ squirrel (T. douglasii), which is found in coniferous forests along the Pacific Coast, from south-western British Columbia to the northern half of California. Both these species are much smaller than the Sciurus species.
American red squirrel, feeding on an acorn, Mackworth Island, Maine. (Photo copyright © by Kaj Halberg)
This Douglas’ squirrel is feeding on a cone of sugar pine (Pinus lambertiana), which is larger than itself. – Yosemite National Park, California. (Photo copyright © by Kaj Halberg)
Two species of flying squirrel are found in North America, the northern (Glaucomys sabrinus) and the southern (G. volans). Despite their name, flying squirrels cannot really fly, but between their forelegs and hindlegs is a large fold of skin, which, when spread out, assists them in gliding from one tree to another. This skin fold contains muscles, making it possible for the squirrel to manoeuvre in the air. Despite being fairly common, the two species are rarely observed, as they are strictly nocturnal, spending the daytime hours sleeping in their nest, which is often an abandoned woodpecker hole. They do not really hibernate in the winter, but spend long periods being inactive, in order to save energy. Often up to 6 animals huddle together to keep warm.
The remaining species of North American squirrels are mainly ground-dwellers. The prairie dogs are already dealt with above. 31 other species of ground squirrels – formerly all included in the genus Spermophilus, but today split into several genera – are distributed across North America, from Mexico to the Arctic. Most species are plain- or bi-coloured, a few with spots or stripes. However, the golden-mantled ground squirrel (Callospermophilus lateralis), which lives in the far West, is gorgeously coloured – certainly one of the most beautiful squirrel species in the world.
The generic name Spermophilus is from the Greek, sperma (‘seed’) and philos (‘fond of’), thus meaning ‘seed-lover’. Most ground squirrels do indeed eat mainly seeds. Arctic ground squirrels (Urocitellus parryii) are much hunted by Arctic people, who eat them and use their pelts to line their parkas.
From a coastal rock in Point Lobos State Natural Reserve, California, this Californian ground squirrel (Otospermophilus beecheyi) keeps a sharp lookout for enemies like coyotes (Canis latrans), hawks, and eagles. (Photo copyright © by Kaj Halberg)
As its name implies, the rock squirrel (Otospermophilus variegatus) is found in rocky areas. This one lives at the edge of the abyss of the Grand Canyon, Arizona. (Photo copyright © by Kaj Halberg)
Have you got a peanut for me? – Tourists often feed the rock squirrels at Grand Canyon. (Photo copyright © by Kaj Halberg)
Occasionally, rock squirrels climb trees. This one is eating flowers of a cottonwood tree (Populus) in Canyon de Chelly National Monument, Arizona. (Photo copyright © by Kaj Halberg)
Young Townsend’s ground squirrels (Urocitellus townsendii), peeping out from their den, Hart Mountains, Oregon. (Photo copyright © by Kaj Halberg)
The common name of the five species of antelope squirrel (Ammospermophilus) was given in allusion to their habit of flashing the white underside of their tail as a warning signal to other squirrels in case of danger – just like the pronghorn, or American antelope, which flashes the white hairs on its rump.
Antelope squirrels mainly live in hot desert areas. They are active during the day, but instead of getting rid of excess heat by evaporating precious water, they in fact store the heat in their body – they get fever! Only if their body temperature exceeds 45oC, will they move underground to cool off.
The white-tailed antelope squirrel (Ammospermophilus leucurus) is the most widespread of the five species within this genus. It can be identified by the reddish fur on its limbs. – Joshua Tree National Park, California. (Photo copyright © by Kaj Halberg)
Harris’s antelope squirrel (Ammospermophilus harrisii) is greyer than white-tailed, with brownish fur on its limbs. – Tucson Mountain Park, Arizona. (Photo copyright © by Kaj Halberg)
Chipmunks – the smallest
Formerly, all 25 species of the tiny chipmunks were placed in one genus, Tamias, but with the exception of the eastern chipmunk (Tamias striatus) and the Siberian chipmunk (Eutamias sibiricus), all species have now been moved to the genus Neotamias. Incidentally, the Siberian is the only chipmunk found outside America.
Of the 24 North American species, only two, the eastern and the least (Neotamias minimus), are found in the eastern half of the continent, while the others are distributed in a variety of habitats in the West, many of them with a rather limited distribution. The name chipmunk was originally spelt chitmunk, from a native Ojibwa word, jidmoonh, meaning ‘red squirrel’.
All chipmunks have white and black (or dark brown) stripes in their face, and along the back are five dark and four white stripes. Their cheek pouches are very large. The generic name Tamias is from the Greek, meaning ‘house-keeper’, or ‘storer’, referring to the habit of these animals to deposit nuts and other seeds in several underground caches, in order to have a supply of food, should they wake up during the winter, and also when they emerge early in spring. One such cache contained 6 kilograms of food, including 3,000 hazelnuts and c. 1.5 kilos of wheat.
Eastern chipmunk (Tamias striatus), resting at the entrance to its nesting hole, Wildwood State Park, Long Island, New York. (Photo copyright © by Kaj Halberg)
Least chipmunk (Neotamias minimus), Black Hills, South Dakota. This tiny species has a very wide distribution, found in most of Canada (except Arctic areas), around the Great Lakes, and in the western half of the U.S. (Photo copyright © by Kaj Halberg)
Lodgepole chipmunk (Neotamias speciosus), sitting on a tree stump, Yosemite National Park, California. This handsome chipmunk is found in the Sierra Mountains of California, with isolated populations in the San Bernardino and San Jacinto Mountains near Los Angeles. (Photo copyright © by Kaj Halberg)
A confiding Townsend’s chipmunk (Neotamias townsendii), taking food from a trekker’s hand, Garibaldi Provincial Park, British Columbia. (Photo copyright © by Kaj Halberg)
This golden retriever, watching a confiding Townsend’s chipmunk, later sniffed it without harming it. – Reedsport, Oregon. (Photo copyright © by Kaj Halberg)
Yellow-pine chipmunk (Neotamias amoenus), feeding on a pine cone, Bend, Oregon. (Photo copyright © by Kaj Halberg)
Marmots – the largest
The remaining group of North American ground-dwelling squirrels are the marmots, comprising six species. They are the largest and fattest of squirrels, growing up to 60 centimetres long and weighing up to 7 kilograms. Five of the six species live mainly in open rocky areas in the West, but one species, the woodchuck (Marmota monax), is found in forests in the eastern and northern parts of the continent. In areas, where the woodchuck is not hunted, it also lives near fields and gardens, often doing damage to crops.
Marmots live in burrows up to 2 metres underground, digging tunnels up to 10 metres long. They often sit on their haunches outside their burrow, and their shrill warning whistles can be heard far away. Marmots are almost exclusively vegetarians. They do not make food deposits, but in autumn they have become extremely fat, and hibernate throughout the winter. Arctic hunters kill many hoary (M. caligata) and Alaskan marmots (M. broweri), eating their delicious meat and using their soft underfur to make parkas.
In his book My First Summer in the Sierra, published in 1911, Scottish-American writer and environmentalist John Muir (1838-1914) writes: “The (marmot) of the bleak mountains is a very different sort of mountaineer – the most bovine of rodents, a heavy eater, fat, aldermanic in bulk and fairly bloated, in his high pastures, like a cow in a clover field. One woodchuck would outweigh a hundred chipmunks, and yet he is by no means a dull animal. In the midst of what we regard as storm-beaten desolation he pipes and whistles right cheerily, and enjoys long life in his skyland homes.”
Yellow-bellied marmot (Marmota flaviventris), resting on a rock, Sequoia National Park, California. (Photo copyright © by Kaj Halberg)
IUCN Red List of Threatened Species, 2017: Cynomys gunnisoni, C. leucurus, C. mexicanus, C. parvidens, website: iucnredlist.org
Macdonald, D. (ed.) 1984. The Encyclopedia of Mammals. Facts on File
Truett, J.C. et al. 2014. Prairie Dogs in the Chihuahuan Desert: History, Ecology, Conservation. In: C.A. Hoyt & J. Karges (eds.). Proceedings of the Sixth Symposium on the Natural Resources of the Chihuahuan Desert Region, October 14-17, 2004, pp. 211-240. The Chihuahuan Desert Research Institute, Fort Davis, Texas
Whitaker, J.O. 1980. The Audobon Society Field Guide to North American Mammals. Alfred A. Knopf
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(Revised October 2018)