Columbian Ground Squirrel

Taxobox
name = Columbian Ground Squirrel


status = LR/lc | status_system = IUCN2.3
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Rodentia
familia = Sciuridae
genus = "Spermophilus"
species = "S. columbianus"
binomial = "Spermophilus columbianus"
binomial_authority = (Ord, 1815)
synonyms = The Columbian Ground Squirrel ("Spermophilus columbianus") is a species of rodent in the Sciuridae family. It is found in Canada and the United States.

=Appearance=In comparison to other species of ground squirrel, "S. columbianus" is one of the largest (Manville, 1959; Eliot 1991). Adult "S. columbianus" can weigh anywhere from 400 grams to 680 grams, and typically finish growing by their third year (Manville, 1959; Eliot, 1991). The squirrel has a reddish brown head, which then transitions into a grayish or occasionally tawny body. They tail is also gray, and may have some white on the dorsal side. Its body is short and thick, and its tail is moderately bushy (Manville, 1959). The total body length may range from 325 millimeters to 410 millimeters (Eliot 1991).

=Habitat=The Columbian Ground Squirrel is found in the Northwestern United States and South Western Canada (Eliot 1991). Specifically, they are found in parts of Montana, Idaho, Oregon, and Washington in the United States. In Canada, they are found largely in British Columbia and on the western edges of Alberta. Within these regions "S. columbianus" can be found in alpine and sub-alpine elevations (Turner, 1972). In cases where "S. beldingi" is present, "S. columbianus" is found at a higher, wetter, location. However, when "S. beldingi" is not present, "S. columbianus" can be found at higher and lower elevations (Turner, 1972). In general though, Columbian ground squirrels are found between elevations of 300 and 2500 meters (Harris 1982). "S. columbianus" is found primarily in meadow and grassland that is prone to flooding, or is typically wet (Eliot, 1991). The squirrels will move between meadow, and light brush throughout their active season. Some have postulated that this movement between locations could be for social networking, and defense against predators (Weddell 1989). Columbian ground squirrels live in self constructed dens. Their burrow system is fairly elaborate and can be wide ranging. The burrow system can expand anywhere from five to seven meters each year (Eliot 1991). Burrow systems are typically used for day to day living, and hibernation, while nesting sites are on the periphery of the burrow system, and were distinctly separated (McLean 1978). Occasionally, a den separate from the active season will be constructed for hibernation (Eliot 1991).

=Predation=The Columbian ground squirrel faces a large number of predators from both the ground and air. Predators on the ground consist of: brown bears ("Ursus arctos"), coyotes ("Canis latrans"), marten ("Martes americana"), badgers ("Taxidea taxus"), lynx ("Felis lynx"), weasels ("Mustela" sp.), and mountain lions ("Felis concolor") (Eliot 1991). There are also numerous avian predators such as: golden eagles ("Aquila chryaetos"), red-tailed hawks ("Buteo jamaicensis"), and goshawks ("Accipiter gentilis") (Eliot 1991). Only predation by badgers has been studied in depth, in regards to its effects on the Columbian ground squirrel (Murie 1992). Badgers tend to attack juveniles in the nest. They do this because the young squirrels have not yet developed the ability to recognize and avoid predators (Murie 1992). Badgers have a significant effect on the population of the ground squirrels. Nests that got attacked only had one or more juvenile emerge 41% of the time (Murie 1992). In one year, badger predation eliminated 56% of the juveniles born (Murie 1992).

=Diet=The Columbian ground squirrel is a forager that has a very wide ranging diet. They typically eat vegetation such as roots, bulbs, stems, flowers and seed capsules, although they have also been documented eating insects as well (Manville, 1959). Early in their active period, the squirrels will eat a variety of grasses and sedges. Later on their active period, they will consume a large amount of fruit and seeds, such as currants, gooseberries, strawberries, and whortleberries (Manville, 1959). Despite their wide ranging diet, Columbian ground squirrels have to eat a very specific diet as their active period winds down in order to be prepared for their long hibernation period. Since their bodies survive off of fat stores during hibernation, the Columbian ground squirrels will greatly increase the amount of fat they eat, particularly polyunsaturated fat (Frank 1994). The squirrels get this polyunsaturated fat from plants that are high in cellulose.

=Spring emergence & Hibernation=Columbian ground squirrels hibernate for a majority of the year. The typical length of hibernation lasts 8 months (Murie, 1984). In most cases, "S. columbianus" goes into hibernation in early August and emerges in mid to late April. Thus, the average active season is about 90-100 days long (Eliot 1991). Unlike some species that will hibernate in groups to help reduce heat loss and maintain fat stores such as the alpine marmot, Columbian ground squirrels hibernate individually (Neuhaus 2000). Thus, with such a long hibernation, a great demand is put on the squirrels to eat an appropriate diet, and gain enough mass and fat stores to survive the hibernation season. Female squirrels are under a great deal of pressure to be prepared for hibernation if they are to successfully wean a litter of offspring. Adult females, on average, emerge from hibernation, a few weeks after their male counterparts; which on average is around the end of April (Harris, 1982). Females mate within the first few days of emerging from hibernation (Neuhaus 2000). If they are not successful initially, they will continue to mate for up to six more weeks (Eliot 1991). Depending on whether or not they are successful during mating will greatly affect the females’ activity during the active period. Male squirrels are the first to emerge from their hibernacula, typically in mid-April. They will mate with the females within a few days of their emergence, and then return to their own activity shortly thereafter. After mating season, the males focus particularly on gaining fat stores for their upcoming hibernation. Adult males typically enter hibernation in the first week of August (Neuhaus 2000). Females who successfully get pregnant will see their energy demands dramatically increase. As is the case with all pregnancies in the animal world, the pregnant female’s energy demands go up significantly while she is gestating. Upon giving birth, the female will need to care for her young for up to a month (Eliot 1991). After successfully weaning them, the female then needs to recover and replace any lost fat stores (Neuhaus 2000). Due to weight loss, and delayed weight gain and fat storage, females that successfully weaned a litter of offspring tend to enter hibernation more than a week later than their unsuccessful counterparts (Neuhaus 2000). Unsuccessful females will not have the added stress of having to wean a litter of offspring, and will focus on putting on enough weight to survive their hibernation. Unsuccessful females typically enter hibernation earlier than their successful counterparts (Neuhaus 2000). It has been postulated that the unsuccessful females will enter into hibernation in late July because food is becoming scarcer, and the risk of predation is increasing (Neuhaus 2000). Juveniles typically emerge from their nests in the first weeks of June (Harris 1982). This gives them a very limited amount of time to accumulate the necessary body fat reserves to survive their first hibernation. This type of time constraint impacts the rate of survival for juveniles (Harris 1982). Juveniles that are lighter than normal from lack of fat storage tend to have a significantly lower survival rate than those that are at the average, or above it (Murie 1984). Thus, juveniles are at a distinct disadvantage when compared to adults in preparing for hibernation.

References

* Rodent Specialist Group 1996. [http://www.iucnredlist.org/search/details.php/42466/all Spermophilus columbianus] . [http://www.iucnredlist.org 2006 IUCN Red List of Threatened Species. ] Downloaded on 30 July 2007.