Richardson's Ground Squirrels

Species Description of Richardson's Ground Squirrels
(also known as gophers)

Richardson's ground squirrels (Urocitellus richardsonii, formerly Spermophilus richardsonii), colloquially known as gophers, are medium-sized rodents; they are larger than mice and voles, smaller than muskrats and beavers, and approximately the size of lab rats. Their closest relatives are chipmunks, prairie dogs, marmots, tree squirrels, and other species of ground squirrels. Because of superficial similarity in appearance between Richardson's ground squirrels and black-tailed prairie dogs (Cynomys ludovicianus), these two species are often confused, especially in the pet trade.  See Similar Species

Taxonomy

Richardson's ground squirrels are named in honour of Sir John Richardson, the surgeon-naturalist on two 19th century British naval expeditions charged with mapping the arctic coast of British North America (now Canada). These expeditions, led by Sir John Franklin, sailed into Hudson Bay and used a land route to reach the arctic coastline of regions now known as Nunavut and Northwest Territories in Canada. After wintering south of Hudson Bay and before heading north to the arctic, John Richardson explored along the Saskatchewan River to Fort Carlton (north of modern-day Saskatoon), where he collected specimens of a new rodent species in May 1820. He sent these specimens back to England, where Joseph Sabine of the Linnean Society assigned the specific epithet richardsonii in John Richardson's honour.

The first drawings of Richardson's ground squirrels were made by people in Europe in the early 1800s who had only seen dead specimens, so their depictions were not very accurate.

drawing of a ground squirrels

The scientific name that Joseph Sabine gave to the species in 1822 was Arctomys richardsonii. In the early 1800s, however, the science of taxonomy was still in its infancy and rapidity of communication amongst scientists was slow before the age of telegraph, telephone, text messaging, and email. The genus name Arctomys was soon replaced by two other names, Citellus and Spermophilus. Eventually, zoologists agreed that all the ground squirrels belonged in the genus Spermophilus. However, with the advent of molecular information that can be combined with cranio-dental variables and morphological characters in sophisticated statistical analyses, scientists now recognize that 1) North American ground squirrels do not form a monophyletic group with European and Asian species and 2) six clades occur within the North American species.  Those six clades have been given six different generic names.  Thus, since 2009, the scientific name of the Richardson's ground squirrel has changed from Spermophilus richardsonii to Urocitellus richardsonii.  The correct common name remains Richardson's ground squirrel, but local names such as gopher, prairie gopher, flickertail, and picket-pin persist in various parts of the geographic range of the species.

The complete taxonomy for Richardson's ground squirrels is:
Kingdom    Animalia
  Phylum     Chordata
    Subphylum   Vertebrata
      Class    Mammalia
        Order    Rodentia
          Family    Sciuridae
            Genus    Urocitellus
              Species    Urocitellus richardsonii

Appearance

Richardson's ground squirrels have an overall uniform appearance, with no spots or stripes anywhere on the body. Fur colour varies with age and season.

When 4- to 7-weeks old, juveniles have soft greyish tan fur. Juveniles then moult into a cinnamon tan coat.

litter of ground squirrels

Newly emerged litter of Richardson's ground squirrels.  These juveniles are 30 days old.

 

ground squirrel profile

Juvenile Richardson's ground squirrel aged 75 days that has moulted into its juvenile pelage.

 

Adults are buffy grey to sandy brown, with indistinct dappling on the uppersides and light tan or buff around the head and undersides. Shortly before entering hibernation, the fur coat of both juveniles and adults becomes paler, verging on light grey.

pre-hibernation ground squirrel

Adult female Richardson's ground squirrel immediately before entry into hibernation. 

 

Albino (pure white fur with red eyes and pink claws) and melanistic (jet black fur) Richardson's ground squirrels are occasionally reported; these color variants are due to recessive genes. 

albino ground squirrel

black ground squirrel

Albino and melanistic Richardson's ground squirrels from Alberta, Canada. 

 

An even rarer colour variant has mostly white fur with scattered black guard hairs and black eyes.

white ground squirrel

White (but not albino) Richardson's ground squirrel from Saskatchewan, Canada. 

 

Adult Richardson's ground squirrels measure approximately 30 cm from the tip of the nose to the tip of the tail. The tail is approximately 7.4 cm long, with dark brown hairs down the middle and light tan or buff hairs below. Compared with the bushy tails of tree squirrels, the fur on the tail is short, but the hairs fluff up somewhat when the animal is agitated.

The ears are small and closely appressed to the head. The eyes are black and place high on the head, enabling the animal to detect approaching danger from almost any direction.

The dental formula for Richardson's ground squirrels is:
i: 1/1 c: 0/0 p: 2/1 m: 3/3 total: 22

meaning that they have:

  • 1 pair of incisors in the upper jaw and 1 pair of incisors in the lower jaw;
  • no canine teeth in either jaw;
  • 2 pairs of premolars in the upper jaw and 1 pair in the lower jaw;
  • 3 pairs of molars in the upper jaw and 3 pairs of molars in the lower jaw

 

ground squirrel skull

ground squirrel jaw

As with other species in the rodent family, there is a gap (diastema) between the incisors and premolars due to the absence of canine teeth. The incisors grow continuously, with the upper and lower incisors continually wearing against each other during normal foraging, creating a beveled edge. The mandibles of the lower jaw are not fused, so the lower incisors can spread apart.

Male Richardson's ground squirrels are larger than females. Weight varies during the annual cycle, but typical weights of adults are 250-400 g for females and 350-500 g for males. (see annual weight cycle)

Related Pages:
Annual Weight Cycle
Evolutionary History

Source: PDF of this article can be downloaded from the Michener Publications page

  • Michener, G.R., and J. W. Koeppl. 1985. Spermophilus richardsonii. Mammalian Species, 243: 1-8.
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