Cascade golden-mantled ground squirrel

Cascade golden-mantled ground squirrel
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Sciuridae
Genus: Callospermophilus
Species: C. saturatus
Binomial name
Callospermophilus saturatus
(Rhoads, 1895)
Synonyms

Spermophilus saturatus

The Cascade golden-mantled ground squirrel (Spermophilus saturatus) is a species of rodent in the family Sciuridae, in the order Rodentia.[2] It is the largest species of the three within the subgenus Callospermophilus.[2] It is found in the Cascade Mountains in the province of British Columbia, Canada and the state of Washington, United States.[1][3]

Morphology

Larger in size than its S. madrensis and S. lateralis counterparts, S. saturatus has a vague russet color outlining its head and shoulders and running down the length of its body (at least 286 mm).[2]

Distribution

S. saturatus occurs in the northwestern United States, north of the Columbia River, south of the Tulameen River in British Columbia, and west of the Similkameen River.[2] No fossils have yet been found.[2] S. saturatus is isolated from its sister species S. lateralis by the Columbia River; their differentiation is likely due to allopatric speciation.[4]

Physiology

At birth, S. saturatus are ectothermic.[5] Development of endothermy occurs gradually as individuals grow, increasing both body mass and amount of body fur.[5] Individuals removed from their mother at 6 days of age lost body temperature at a faster rate than at 36 days, when individuals were able to maintain a high internal body temperature and determined to be homeothermic.[5] This 36-day mark is conveniently the age at which offspring leave their burrows.[5] Individuals remained homeothermic in response to a 2-day removal of food and water at 2-week intervals.[5] Even with this drastically reduced body mass, torpor was not induced.[5] Smaller individuals did become hypothermic, however, and were returned to the mother to be re-warmed.[5]

Daily energy expenditures showed a small but significant increase of 10% as litter size increased, across a range of 3 to 5 offspring, the norm for the species.[6] Body mass, time spent above ground and time spent foraging were not correlated.[6] For the large amount energy contained in the mother’s milk, changes in metabolism were small.[6] Body mass and age of offspring was independent of litter size.[6] The fact that daily energy expenditure does not vary with litter size suggests that other factors, such as habitat quality, affect number of offspring.[6]

S. saturatus have been noted to move in two distinct ways – walking (mean speed of .21 m/s) and running (mean speed of 3.63 m/s).[7] 26.9% of total time spent daily above ground was spent walking, while only 3.6% was spent running.[7] It is noted that individuals run at their maximum aerobic speed of 3.6 m/s instead of the more maintainable minimum running pace of 2 m/s in order to minimize predation.[7] S. saturatus moved an average of 5 km/day – 1.5 km walking and 3.3 km running.[7] This considerable distance required 28.75 kJ/day of net added energy cost to do so, a 29% increase above BMR and 13% of daily energy expenditure.[7]

Behavior

Examination of alarm calls in response to Canis lupus familiaris among several species of ground squirrels showed that S. saturatus have a dialect of their own.[4] Vocalizations were distinct, and could be identified 100% of the time by a discriminant source.[4] This suggests that vocalizations can be used in addition to genetics and morphology to differentiate and designate species.[4]

A Cascade golden-mantled ground squirrel on Mount Rainier.

References

  1. 1 2 Linzey, A. V. & Hammerson, G. (2008). "Spermophilus saturatus". IUCN Red List of Threatened Species. Version 2008. International Union for Conservation of Nature. Retrieved 8 January 2009.
  2. 1 2 3 4 5 Trombulak, Stephen C. (27 December 1988). "Spermophilus saturatus" (PDF). Mammalian Species.
  3. ↑ Helgen, Kristofer M.; Cole, F. Russel; Helgen, Lauren E.; Wilson, Don E (2009). "Generic Revision in the Holarctic Ground Squirrel Genus Spermophilus" (PDF). Journal of Mammalogy. 90 (2): 270–305. doi:10.1644/07-MAMM-A-309.1. Archived from the original (PDF) on 22 October 2011.
  4. 1 2 3 4 Eiler, Karen Christine; Banack, Sandra Anne (Feb 2004). "Variability in the Alarm Call of Golden-Mantled Ground Squirrels (Spermophilus lateralis and S. saturatus)". Journal of Mammalogy. JSTOR 1383975.
  5. 1 2 3 4 5 6 7 Geiser, Fritz; Kenagy, G. J. (Aug 1990). "Development of Thermoregulation and Torpor in the Golden-Mantled Ground Squirrel Spermophilus saturatus". Journal of Mammalogy. JSTOR 1381938.
  6. 1 2 3 4 5 Kenagy, G. J.; Masman, D.; Sharbaugh, S. M.; Nagy, K. A. (Feb 1990). "Energy Expenditure During Lactation in Relation to Litter Size in Free-Living Golden-Mantled Ground Squirrels". Journal of Animal Ecology. JSTOR 5159.
  7. 1 2 3 4 5 Kenagy, G. J.; Hoyt, Donald F. (Dec 1989). "Speed and Time-Energy Budget for Locomotion in Golden-Mantled Ground Squirrels". Ecology. JSTOR 1938116.
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