(Thamnophis sirtalis tetrataenia)
Family: Colubrid Snakes (Colubridae)
Order: Scaly Reptiles or Squamates (Squamata)
| |
San Francisco Garter Snake
(Thamnophis sirtalis tetrataenia) Family: Colubrid Snakes (Colubridae) Order: Scaly Reptiles or Squamates (Squamata) |
|
|
Size: Maximum length for the species is 140 cm, but whether the San Francisco Garter Snake reaches this size is uncertain. Distribution: This Garter Snake is found in only two counties in California, near San Francisco. It is a subspecies (race) of the Common Garter Snake (T. sirtalis), which in general is found from southern Alaska (the only native snake species in Alaska) through southern Canada, large parts of USA, south to northern Mexico. It is the most widely distributed snake species in North America. Habitat: The species in general occupies a wide range of aquatic, wetland, and upland habitats. The San Francisco Garter Snake prefers densely vegetated, wet, marshy areas, often near exposed hillsides, where it can sun and feed. It can also be observed basking on floating algal or rush mats. Food: Primarily small frogs, particularly the California Red-legged Frog (Rana aurora), which is federally listed as endangered. The youngs feed on Pacific Treefrogs (Hyla regilla) and are so dependent on this food source that they may not survive where treefrogs are not present. Also juvenile Bullfrogs (Rana catesbeiana) may be eaten. The toxic California Newt (Taricha torosa) is also taken, and the garter snake is one of the few animals which can eat these newts without resulting sickness or death. Reproduction: Mating takes place in spring or autumn, and the female gives birth to as many as two dozen (average 16) youngs in June to September, which measure 12-18 cm at birth. In other populations clutches may contain as many as 85 youngs, making it one of the most prolific snakes known. The youngs mature after two years. In Manitoba, Canada, huge aggregations of snakes which could number tens of thousands of snakes, could earlier be observed as the snakes were coming out from hibernation to mate. However, the number of snakes in these aggregations have declined alarmingly in recent years. Activity and behaviour: Mainly diurnal, but may be crespuscular or nocturnal during warm summer nights. This subspecies hibernates during winter, but some other populations of the species are active all through the year. They wander up to several hundred meters upland to hibernate in small mammal burrows. Enemies and defense: Adults of the introduced Bullfrog (Rana catesbeiana) prey on garter snakes and may be a cause of decline in this endangered snake subspecies. Longevity: Record longevity for the species is about 10 years. Sexual differences: Females are bigger than males. Status: The species in general is widely distributed, common over much of its range, and unlikely to be declining. In some northern populations, very large aggregations may be encountered during mating season. Total population is unknown, but has been estimated to more than 1 million. IUCN Red List Category rating: Least Concern. However, the San Francisco Garter Snake has been listed as an endangered snake since 1967. The wild population is, at least partially, in decline and has been estimated to 1,000-2,000 individuals, but may be larger, due to its elusive and extremely shy nature, which makes it difficult to obtain reliable population statistics. Moreover, much of the remaining suitable habitats are on private property which has not been surveyed. In many areas where it still occurs it is quite common, though, and not necessarily difficult to observe. Major threats are habitat destruction, due to land development, illegal collecting for the pet trade, and possibly the introduced predator, the Bullfrog. Notes: The San Francisco Garter Snake has previously been confused with the California Red-sided Garter Snake (T. s. infernalis) and the Oregon Red-spotted Garter Snake (T. s. concinnus), and although currently recognized as valid subspecies, the status of he subspecies is still unresolved. References: Anonymous. 1980. Survival of the San Francisco garter snake. Herpetology (Pasadena) 10(3): 3-4. Banks, R.C.; McDiarmid, R.W.; Gardner, A.L. (eds.). 1987. Checklist of vertebrates of the United States, the U.S. Territories, and Canada. U.S. Fish and Wildlife Service Resource Publication 166: 1-79. Barry, S.J.; Jennings, M.R. 1998. Case 3012. Coluber infernalis Blainville, 1835 and Eutaenia sirtalis tetrataenia Cope in Yarrow, 1875 (Currently Thamnophis sirtalis infernalis and T. s. tetrataenia; Reptilia, Squamata): proposed conservation of the subspecific names by the desig# Bulletin of Zoological Nomenclature 55(4): 224-228. Barry, S.J.; Jennings, M.R.; Smith, H.M. 1996. Current subspecific names for western Thamnophis sirtalis. Herpetological Review 27(4): 172-173. Behler, J.L.; King, F.W. 1979. The Audubon Society field guide to North American reptiles and amphibians. Alfred A. Knopf, New York. 719 pp. Bourguignon, T. 2002. Strumpfbandnattern: Herkunft - Pflege - Arten. Ulmer, Stuttgart. 125 pp. Brode, J.; Hansen, R.W.; Keel, P. 1994. San Francisco garter snake. pp. 280-281. In: Thelander, C.G. & Crabtree, M. (eds.): Life on the edge: a guide to California's endangered natural resources: wildlife. Biosystems Books, Santa Cruz, California. 550 pp. Cover, J.F.; Boyer, D.M. 1988. Captive reproduction of the San Francisco garter snake Thamnophis sirtalis tetrataenia. Herpetological Review 19(2): 29-30, 32-33. Ernst, C.H.; Ernst, E.M. 2003. Snakes of the United States and Canada. Smithsonian Books, Washington & London. 668 pp. Fisher, C.; Joynt, A.; Brooks, R.J. 2007. Reptiles and amphibians of Canada. Lone Pine Publishing, Edmonton. 208 pp. Frost, D.R., Hammerson, G.A. & Santos-Barrera, G. 2007. Thamnophis sirtalis. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. (Accessed 22nd April 2011). Gebauer, J. 2006. Strumpfbandnattern in der Wissenschaft. Draco 7(1) (25): 60-65. Hallmen, M. 1999. Aufzucht und Haltung der San Francisco Strumpfbandnatter Thamnophis sirtalis tetrataenia. Herpetofauna (Weinstadt) 21(120): 20-24. Hallmen, M. 2006. Altes und Neues von der San-Francisco-Strumpfbandnatter (Thamnophis sirtalis tetrataenia). Draco 7(1) (25): 25-31. Hallmen, M. 2006. Strumpfbandnattern im Freilandterrarium. Draco 7(1) (25): 102-111. Hallmen, M.; Chlebowy, J. 2001. Strumpfbandnattern. Natur und Tier-Verlag, Münster. 191 pp. Janzen, F.J.; Krenz, J.G.; Haselkorn, T.S.; Brodie, E.D.; Brodie, E.D. 2002. Molecular phylogeography of common garter snakes (Thamnophis sirtalis) in western North America: Implications for regional historical forces. Molecular Ecology 11(9): 1739-1751. Kaplan, M. 1995. Not-so-common garters. Litteratura Serpentium (English Edition) 15(5): 114-117. Liner, E.A. 2007. A checklist of the amphibians and reptiles of México. Occasional Papers of the Museum of Natural Science Louisiana State University 80: 1-60. Mutschmann, F. 1995. Die Strumpfbandnattern: Biologie, Verbreitung, Haltung. Westarp Wissenschaften, Magdeburg. 172 pp. Rightmire, J.E. 2001. Some threatened U.S. snakes: five species on the red list. Reptile & Amphibian Hobbyist 6(10): 27-32. Rogner, M. 1992. Strumpfbandnattern. TI-Magazin 110: 54-57. Rossman, D.A.; Ford, N.B.; Seigel, R.A. 1996. The garter snakes: evolution & ecology. Vol. 2. University of Oklahoma Press, Norman & London. 332 pp. Smith, H.M. 1999. Comment on the proposed conservation of Coluber infernalis Blainville, 1835 and Eutaenia sirtalis tetrataenia Cope in Yarrow, 1875 (currently Thamnophis sirtalis infernalis and T. s. tetrataenia; Reptilia, Squamata): proposed conservation of the s# Bulletin of Zoological Nomenclature 56(1): 71-72. Stanislawski, W. 1991. The San Francisco garter snake, Thamnophis sirtalis tetrataenia - the first experiences in maintaining at the Zoological Garden of Lodz. Zoologische Garten 61(4): 267-270. Stebbins, R.C. 2003. A field guide to western reptiles and amphibians. 3rd edition. Houghton Mifflin Company, Boston & New York. 533 pp. Tonge, S.J.; Bloxam, Q.M.C. 1986. The San Francisco garter snake Thamnophis sirtalis tetrataenia at the Jersey Wildlife Preservation Trust. Dodo 23: 112-114. Wikipedia. San Francisco Garter Snake. (http://en.wikipedia.org/wiki/San_Francisco_Garter_Snake). (Accessed 20th April 2011). Text & layout: Rune Midtgaard |
|
