San Francisco garter snake
Encyclopedia
The San Francisco Garter Snake (Thamnophis sirtalis tetrataenia) is a slender multi-colored colubrid
snake
. Designated as an endangered species
since the year 1967, it is endemic to California and resides only in San Mateo County, California
, and the extreme northern part of coastal Santa Cruz County, California
. Some researchers estimate that there are only 1,000 to 2,000 adult snakes of the subspecies
T. s. tetrataenia remaining, however, the full extent of the snakes habitat has not been fully documented and many snakes may utilize creeks and other waterways that are currently unexplored. This garter snake prefers wet and marshy areas and is elusive to see or capture. It is a subspecies of the common garter snake
(Thamnophis sirtalis), a species found across the United States
and into southern Canada
.
, at least to the Upper Crystal Springs Reservoir
, and along the Pacific
coast south to Año Nuevo Point, and thence to Waddell Creek in Santa Cruz County. It is difficult to obtain reliable distribution information and population statistics for the San Francisco garter snake, because of the elusive nature of this reptile and the fact that much of the remaining suitable habitat is located on private property that has not been surveyed for the presence of the snake. This subspecies is extremely shy, difficult to locate and capture, and quick to flee to water or cover when disturbed. The U.S. Fish and Wildlife Service has stated that many locations that previously had healthy populations of garter snakes are now in decline due to land development pressure and the filling of wetland
s in San Mateo County over the last sixty years. However, in many areas where it still occurs it is not rare, and is actually quite common and can be viewed with good success once its behavior is understood.
The snake’s preferred habitat
is a densely vegetated pond near an open hillside where it can sun, feed, and find cover in rodent
burrow
s; however, markedly less suitable habitat can be successfully used. Temporary pond
s and other seasonal freshwater
bodies are also appropriate. This subspecies avoids brackish marsh
areas because its preferred prey, the California red-legged frog
(Rana aurora) cannot survive in saline water
. Emergent and bankside vegetation such as cattails, (Typha
spp.), bulrush
es (Scirpus
spp.) and spike rushes (Juncus
spp. and Eleocharis
spp.) apparently are preferred and used for cover. The zone between stream
and pond
habitats and grassland
s or bank sides is characteristically utilized for basking, while nearby dense vegetation or water often provide escape cover. The subspecies occasionally uses floating algal or rush mats, when available.
San Francisco garter snakes forage extensively in aquatic habitats
. Adult snakes feed primarily on California red-legged frogs, which are federally listed as threatened. They may also feed on juvenile
bullfrog
s (Rana catesbeiana), but they are unable to consume adults; in fact, adult bullfrogs prey on juvenile garter snakes, and may be a contributing factor in the population decline of the San Francisco garter snake. Newborn and juvenile San Francisco garter snakes depend heavily upon Pacific treefrogs (Hyla regilla) as prey. If newly metamorphosed Pacific treefrogs are not available, the young garter snakes may not survive. San Francisco garter snakes are one of the few animals capable of ingesting the toxic California newt
(Taricha torosa) without incurring sickness or death.
(enter a dormant state) in rodent
burrows during Fall and Spring. Along the Pacific Ocean
coast, snakes hibernate
during the winter, but further inland, if the weather is suitable, this species is known to be active year-round. Recent studies have documented San Francisco garter snake movement over several hundred meters from wetlands to hibernate in upland small mammal burrows. In spite of being reported as a diurnal
, captive and specimens housed in an exterior setting, as well as wild snakes were observed foraging nocturnally
or crepuscular
ly on warm evenings.
The San Francisco garter snake mates in the spring or autumn, and the females give birth to live young in June through September, numbering up to two dozen, but averaging about 16 offspring. The young are approximately 12 to 18 centimeters in length and mature in two years time.
(ICZN) to suppress the changes proposed in 1996 to merge two of these species. In 2000, the ICZN agreed and voted to retain the historical taxonomic
arrangement of subspecies within this evolutionary lineage. Accordingly, the subspecies tetrataenia was reaffirmed for the San Francisco garter snake and the races concinnus and infernalis retain their historical definition.
The San Francisco garter snake cohabits ecosystems that host two other species of garter snake: the coast garter snake (Thamnophis elegans terrestris), a subspecies of Western Terrestrial Garter Snake
(T. elegans), and the Santa Cruz aquatic garter snake (Thamnophis atratus atratus) a subspecies of the aquatic garter snake
(T. atratus). These three subspecies are known to prey upon same foods; however, their preferences are slightly different. Herpetologist Sean Barry notes that they divide up the food resource as follows:
, Contra Costa County
, and Santa Clara County
into a separate group that exhibits an "elevated rate of molecular evolution". The authors suggest that sequencing nuclear DNA
may provide a more precise analytical tool to crack some of the ultimate taxonomic quandaries of the San Francisco garter snake and its relatives.
Due to the sensitive nature of this snake, no current localities where it is found will be cited in this article.
Colubrid
A colubrid is a member of the snake family Colubridae. This broad classification of snakes includes about two-thirds of all snake species on earth. The earliest species of the snake family date back to the Oligocene epoch. With 304 genera and 1,938 species, Colubridae is the largest snake family...
snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
. Designated as an endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
since the year 1967, it is endemic to California and resides only in San Mateo County, California
San Mateo County, California
San Mateo County is a county located in the San Francisco Bay Area of the U.S. state of California. It covers most of the San Francisco Peninsula just south of San Francisco, and north of Santa Clara County. San Francisco International Airport is located at the northern end of the county, and...
, and the extreme northern part of coastal Santa Cruz County, California
Santa Cruz County, California
Santa Cruz County is a county located on the Pacific coast of the U.S. state of California, on the California Central Coast. The county forms the northern coast of the Monterey Bay. . As of the 2010 U.S. Census, its population was 262,382. The county seat is Santa Cruz...
. Some researchers estimate that there are only 1,000 to 2,000 adult snakes of the subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
T. s. tetrataenia remaining, however, the full extent of the snakes habitat has not been fully documented and many snakes may utilize creeks and other waterways that are currently unexplored. This garter snake prefers wet and marshy areas and is elusive to see or capture. It is a subspecies of the common garter snake
Common Garter Snake
The Common Garter Snake is a snake indigenous to North America. Most garter snakes have a pattern of yellow stripes on a brown or green background and their average length is about , maximum about .-Subspecies:...
(Thamnophis sirtalis), a species found across the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and into southern Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
.
Range and habitat
This subspecies of the Common Garter Snake is found in scattered wetland areas on the San Francisco Peninsula from approximately the northern boundary of San Mateo County south along the eastern and western bases of the Santa Cruz MountainsSanta Cruz Mountains
The Santa Cruz Mountains, part of the Pacific Coast Ranges, are a mountain range in central California, United States. They form a ridge along the San Francisco Peninsula, south of San Francisco, separating the Pacific Ocean from San Francisco Bay and the Santa Clara Valley, and continuing south,...
, at least to the Upper Crystal Springs Reservoir
Crystal Springs Reservoir
Crystal Springs Reservoir is a pair of artificial lakes located in the northern Santa Cruz Mountains of San Mateo County, California situated in the rift valley created by the San Andreas Fault just to the west of the cities of San Mateo and Hillsborough, and I-280...
, and along the Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
coast south to Año Nuevo Point, and thence to Waddell Creek in Santa Cruz County. It is difficult to obtain reliable distribution information and population statistics for the San Francisco garter snake, because of the elusive nature of this reptile and the fact that much of the remaining suitable habitat is located on private property that has not been surveyed for the presence of the snake. This subspecies is extremely shy, difficult to locate and capture, and quick to flee to water or cover when disturbed. The U.S. Fish and Wildlife Service has stated that many locations that previously had healthy populations of garter snakes are now in decline due to land development pressure and the filling of wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....
s in San Mateo County over the last sixty years. However, in many areas where it still occurs it is not rare, and is actually quite common and can be viewed with good success once its behavior is understood.
The snake’s preferred habitat
Habitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...
is a densely vegetated pond near an open hillside where it can sun, feed, and find cover in rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
burrow
Burrow
A burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, so the burrowing way of life is quite popular among the...
s; however, markedly less suitable habitat can be successfully used. Temporary pond
Pond
A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens, water features and koi ponds; all designed for aesthetic ornamentation as landscape or architectural...
s and other seasonal freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
bodies are also appropriate. This subspecies avoids brackish marsh
Marsh
In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....
areas because its preferred prey, the California red-legged frog
California Red-legged Frog
The California red-legged frog, Rana draytonii, is a moderate to large species of frog. It is known under the scientific name Rana draytonii, after being long included with the northern red-legged frog The California red-legged frog, Rana draytonii, is a moderate to large (4.4–14 cm) species...
(Rana aurora) cannot survive in saline water
Saline water
Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....
. Emergent and bankside vegetation such as cattails, (Typha
Typha
Typha is a genus of about eleven species of monocotyledonous flowering plants in the family Typhaceae. The genus has a largely Northern Hemisphere distribution, but is essentially cosmopolitan, being found in a variety of wetland habitats...
spp.), bulrush
Bulrush
-Wetland plants:* Bolboschoenus, a genus in the sedge family * Cyperus, a genus in the sedge family * Scirpus, a genus in the sedge family * Schoenoplectus, a genus in the sedge family...
es (Scirpus
Scirpus
The plant genus Scirpus consists of a large number of aquatic, grass-like species in the family Cyperaceae , many with the common names club-rush or bulrush . Other common names are deergrass or grassweed.The genus has a cosmopolitan distribution, and grows in wetlands and moist soil...
spp.) and spike rushes (Juncus
Juncus
Juncus is a genus in the plant family Juncaceae. It consists of some 200 to 300 or more species of grassy plants commonly called rushes...
spp. and Eleocharis
Eleocharis
Eleocharis is a genus of 250 or more species of flowering plants in the sedge family, Cyperaceae. They are known commonly as spikerushes, although spikesedges is a more technically appropriate name and most scientists who study them in earnest refer to them as such...
spp.) apparently are preferred and used for cover. The zone between stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
and pond
Pond
A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens, water features and koi ponds; all designed for aesthetic ornamentation as landscape or architectural...
habitats and grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
s or bank sides is characteristically utilized for basking, while nearby dense vegetation or water often provide escape cover. The subspecies occasionally uses floating algal or rush mats, when available.
San Francisco garter snakes forage extensively in aquatic habitats
Aquatic ecosystem
An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems....
. Adult snakes feed primarily on California red-legged frogs, which are federally listed as threatened. They may also feed on juvenile
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
bullfrog
Bullfrog
The American bullfrog , often simply known as the bullfrog in Canada and the United States, is an aquatic frog, a member of the family Ranidae, or “true frogs”, native to much of North America. This is a frog of larger, permanent water bodies, swamps, ponds, and lakes, where it is usually found...
s (Rana catesbeiana), but they are unable to consume adults; in fact, adult bullfrogs prey on juvenile garter snakes, and may be a contributing factor in the population decline of the San Francisco garter snake. Newborn and juvenile San Francisco garter snakes depend heavily upon Pacific treefrogs (Hyla regilla) as prey. If newly metamorphosed Pacific treefrogs are not available, the young garter snakes may not survive. San Francisco garter snakes are one of the few animals capable of ingesting the toxic California newt
California Newt
The California newt is a newt. It is also referred to as the orange bellied newt. They can grow to be in length.- Physical description :T. torosa adult length can range from to...
(Taricha torosa) without incurring sickness or death.
Life cycle
Adult snakes sometimes estivateEstivation
Aestivation is a state of animal dormancy, characterized by inactivity and a lowered metabolic rate, that is entered in response to high temperatures and arid conditions...
(enter a dormant state) in rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
burrows during Fall and Spring. Along the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
coast, snakes hibernate
Hibernation
Hibernation is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. Hibernating animals conserve food, especially during winter when food supplies are limited, tapping energy reserves, body fat, at a slow rate...
during the winter, but further inland, if the weather is suitable, this species is known to be active year-round. Recent studies have documented San Francisco garter snake movement over several hundred meters from wetlands to hibernate in upland small mammal burrows. In spite of being reported as a diurnal
Diurnal animal
Diurnality is a plant or animal behavior characterized by activity during the day and sleeping at night.-In animals:Animals that are not diurnal might be nocturnal or crepuscular . Many animal species are diurnal, including many mammals, insects, reptiles and birds...
, captive and specimens housed in an exterior setting, as well as wild snakes were observed foraging nocturnally
Nocturnal animal
Nocturnality is an animal behavior characterized by activity during the night and sleeping during the day. The common adjective is "nocturnal"....
or crepuscular
Crepuscular
Crepuscular animals are those that are active primarily during twilight, that is during dawn and dusk. The word is derived from the Latin word crepusculum, meaning "twilight." Crepuscular is, thus, in contrast with diurnal and nocturnal behavior. Crepuscular animals may also be active on a bright...
ly on warm evenings.
The San Francisco garter snake mates in the spring or autumn, and the females give birth to live young in June through September, numbering up to two dozen, but averaging about 16 offspring. The young are approximately 12 to 18 centimeters in length and mature in two years time.
Taxonomy and relation to other garter snakes
For a brief period from 1996 to 2000 there was confusion over the differentiation of the San Francisco garter snake from two other subspecies, known as the California red-sided garter snake (T. s. infernalis) and the Oregon red-spotted garter snake (T. s. concinnus). Barry petitioned the International Commission on Zoological NomenclatureInternational Commission on Zoological Nomenclature
The International Commission on Zoological Nomenclature is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 28 members from 20 countries, mainly practicing zoological taxonomists...
(ICZN) to suppress the changes proposed in 1996 to merge two of these species. In 2000, the ICZN agreed and voted to retain the historical taxonomic
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
arrangement of subspecies within this evolutionary lineage. Accordingly, the subspecies tetrataenia was reaffirmed for the San Francisco garter snake and the races concinnus and infernalis retain their historical definition.
The San Francisco garter snake cohabits ecosystems that host two other species of garter snake: the coast garter snake (Thamnophis elegans terrestris), a subspecies of Western Terrestrial Garter Snake
Western Terrestrial Garter Snake
The Western terrestrial garter snake is a species of colubrid snake.Seven subspecies are currently recognized.-Description:...
(T. elegans), and the Santa Cruz aquatic garter snake (Thamnophis atratus atratus) a subspecies of the aquatic garter snake
Aquatic Garter Snake
The aquatic garter snake, Thamnophis atratus, is a species of colubrid snake. Three subspecies are currently recognized.- Description :Growing up to 18-40 inches long, this snake's dorsal coloration varies greatly...
(T. atratus). These three subspecies are known to prey upon same foods; however, their preferences are slightly different. Herpetologist Sean Barry notes that they divide up the food resource as follows:
- The San Francisco garter snake eats primarily small frogs;
- The coast garter snake eats principally slugs, and
- The Santa Cruz aquatic garter snake eats preferentially minute fish and amphibian larvae.
DNA analysis
While the findings of the ICZN have given the San Francisco garter snake unique taxonomic standing for now, a molecular study challenges the subspecific status of this population. Janzen analyzed sequences in mitochondrial DNA to determine relationships within the common garter snake (T. sirtalis). Janzen found that molecular evidence differed, often sharply, with the territorial boundaries of subspecies named on phenotypic variation. He further deduced that local environmental forces were more significant in shaping the color patterns shown by the garter snakes than shared common ancestry, and concluded all morphologically based subspecies in the western U.S. to be subject to revision. This result strongly suggests that the color traits that are diagnostic for (T.s. tetrataenia) are the result of local selection rather than long-term isolation from other races of (T. sirtalis) in central California. On the other hand, the article places the three nearest populations of T. s. infernalis to T.s. tetrataenia in Sonoma CountySonoma County, California
Sonoma County, located on the northern coast of the U.S. state of California, is the largest and northernmost of the nine San Francisco Bay Area counties. Its population at the 2010 census was 483,878. Its largest city and county seat is Santa Rosa....
, Contra Costa County
Contra Costa County, California
Contra Costa County is a primarily suburban county in the San Francisco Bay Area of the U.S. state of California. As of the 2010 census, it had a population of 1,049,025...
, and Santa Clara County
Santa Clara County, California
Santa Clara County is a county located at the southern end of the San Francisco Bay Area in the U.S. state of California. As of 2010 it had a population of 1,781,642. The county seat is San Jose. The highly urbanized Santa Clara Valley within Santa Clara County is also known as Silicon Valley...
into a separate group that exhibits an "elevated rate of molecular evolution". The authors suggest that sequencing nuclear DNA
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...
may provide a more precise analytical tool to crack some of the ultimate taxonomic quandaries of the San Francisco garter snake and its relatives.
Outlook for this subspecies
Many of the factors that led to the listing of the San Francisco garter snake in 1967 continue to impact the organism. These environmental elements include loss of habitat from agricultural, commercial and urban development as well as collection by reptile fanciers and breeders. Collection of these endangered animals by private citizens remains illegal.Due to the sensitive nature of this snake, no current localities where it is found will be cited in this article.