Appendix W Status and Life History of th e San Francisco Garter Snake ( Thamnophis sirtalis tetrataenia )

1.1 Species Listing Status

The San Francisco Garter Snake (SFGS) ( Thamnophis sirtalis tetrataenia ) was listed as endangered on March 11, 1967 (32 FR 4001; USFWS 1967) by the U.S. Fish and Wildlife Service (USFWS) and was grandf athered under the Endangered Species Act (ESA) when it was signed into law in 1973. A Recovery Plan for the SFGS was approved by the USFWS on September 11, 1985 (USFWS, 1985). In addition, a 5-year review, which provides an updated life hi story for the SFGS, was published by the USFWS in September of 2006 (USFWS, 2006).

1.2 Description

The SFGS is a thin and colorful snake in the Colubridae family, which includes most of the species of snakes found in the western U. S. (USFWS, 2007). SFG Ss range in length from 46 to 131 cm (18 to 51 inches) (USFWS , 1985 and Woodland Park Zoo). Female SFGS typically weigh about 8 oz. (227 g), whereas, males are usually smaller than females and can be half the length and wei ght of females (SF Zoo and Woodland Park Zoo). Garter snakes are usually about tw o inches in girth (Kaplan, 2002). Neonate snakes are 18 to 20 cm in length and disperse immediately after they are born. Juvenile SFGS grow quickly during their first year and spend most of their time feeding. These snakes are typically considered to be mature at two years of age when the males are about 46 cm and the females are about 55 cm; however, some snakes take longer to mature and may not reach maturity until they are three years old. It is estimated that SFGS live between 8 and 15 years (Woodland Park Zoo and Goals Project, 2000).

1.3 Distribution

SFGSs are endemic to the San Francisco Peninsula and San Mateo County and were historically found from San Francisco to Santa Cruz (USFWS, 1985 and 2005), including the San Francisco Peninsula from just north of the San Francisco-San Mateo County line near Lake Merced south along the easter n and western bases of the Santa Cruz Mountains, to the Upper Crystal Springs Rese rvoir, along the coast south to Ano Nuevo Point, in San Mateo County, and Waddell Creek , in the extreme northern portion of Santa Cruz County (USFWS, 1985, 2006, and 2007). Ho wever, the findings of SFGS in Waddell Creek in Santa Cruz County may be questionable (Goals Project, 2000) due to the reported presence of hybr id species in the area.

SFGS populations are thought to have primarily occupied habitat area s in the Buri Buri Ridge along the San Andres Rift Zone from n ear Pacifica, southeast to the Pulgas Water Temple, and in an arc from the San Georgio- Pescadero highlands west to the coast, and south to Ano Nuevo (USFWS, 2006 and Goals Project, 2000). Red-sided garter snake (RSGS) and SFGS hybrids have been found in eastern San Mateo C ounty (southeast of

1the Pulgas Water Temple) and in the extreme western part of Santa Clara County (Goals Project, 2000). The hybrids range from the Pulgas region near Upper Crystal Springs

Reservoir south to Palo Alto (USFWS, 2006).

The extreme northeastern part of the SFGS’ s range may have been represented by a population at San Bruno Mountain; however, it is possible that this population has been extirpated (USFWS, 2006). Th is population may not be natu ral as individual SFGSs may have been moved here in an attempt to protec t them because this area is protected under a Habitat Conservation Plan (HCP) (USFWS, 2006). It is possible that these attempted

conservation methods were also used farther south, resul ting in the population at Half Moon Bay (USFWS, 2006).

The historic range of the SFGS may have extend ed as far south as Stanford in Santa Clara County (USFWS, 2006). This assumption is based on observations of hybrids of the SFGS and other garter snake species in th is area (USFWS, 2006). The USFWS also

believes that areas on the coast west of the Santa Cruz Mountains may be inhabited by the SFGS; however, this cannot be confirme d because this area is privately owned (USFWS, 2006).

Historically, SFGSs were found in sag ponds, small seasonal ponds along the San Andreas Fault in the northern part of the San Francisco Peninsul a (USFWS, 1985). Some believe that the purest SFGS populations we re found on the coast around Sharp Park in Laguna Salada and along the ridge of the San Francisco Peninsula east of Sharp Park (USFWS, 1985). Habitat areas in the north ern and eastern portions of the SFGS’s historical range have been destroyed by urbanization and development, including the SFGS population co-located w ith the sag ponds along the ri dge of the San Francisco Peninsula east of Sharp Park (USFWS, 1985).

Although the SFGS’s geographical range seems extensive, field survey s performed by the USFWS and the California Department of Fish and Game (CDFG) indicate that their range is limited to and locali zed within San Mateo County (U SFWS, 1985). Six areas are known to contain significant populations of SFG S: 1) Ano Nuevo State Reserve (ANSR), 2) Pescadero Marsh Natural Preserve, 3) Sa n Francisco State Fish and Game Refuge (including both Upper and Lower Crystal Spri ngs Reservoirs), 4) Sharp Park (Laguna Salada), 5) Cascade Ranch, and 6) Milbrae or West of Bayshore (n ear the San Francisco Airport) (USFWS, 1985).

The current distribution of th e SFGS is unknown because most of their historic range is now privately owned; however, it appears that the SFGS can stil l be found in much of its historic range (USFWS, 2006 and 2007). SFGSs were found in Upper Crystal Springs Reservoir and Mud Dam in 1998 (San Fran cisco Planning Department, 2001). They

were also observed at “San Andreas Rese rvoir and in a sag po nd between San Andreas and Crystal Springs” (San Francisco Pla nning Department, 2001). Regardless, the number of locations that previously mainta ined healthy populations of the SFGS has declined and SFGS have been extirpated from individual locations within their historic

2range (USFWS, 2007). Currently, wild SFG S populations are limited to coastal San Mateo County and other small pockets (USFWS, 2005).

Some sources state that 65 “permanent” reproductive populations ranging from two to

over 500 adults were found on the San Fran cisco Peninsula (Kaplan, 2002 and Goals Project, 2000). The total SFGS population is believed to be around 1500 snakes over one year old (Kaplan, 2002 and Goals Project, 2000 ). All young under one year old are not included in population counts because the popu lation increases when the young are born and returns to around 1500 the following spring due to insufficient resources (Kaplan, 2002). It is thought that half of the populations are protected to some degree by refuges including preserves and state parks (Goals Project, 2000).

1.3.1 FWS Critical Habitat/ CNDDB Occurrence Data

No critical habitat for the SFGS has b een designated by the USFWS to date.

1.4 Habitat

Successful SFGS breeding populations are ty pically found in densely vegetated ponds near open hillsides where they can sun them selves, feed, and find shelter in rodent burrows; however, less ideal ha bitats can also be occupied (USFWS, 2007). These sites usually include emergent vegetation for c over, basking sites, food sources, upland hibernation sites, and corrido rs which allow for movement between the feeding grounds and the hibernation sites (USFWS, 1985 and 2007). SFGSs prefer shallow marshlands with emergent vegetation and breeding popul ations of both Pacific tree frogs and California red-legged frogs (CRLF) as well as open grassy uplands (USFWS, 2006). Breeding populations of SFGS are not known to exist where amphibians are not found (USFWS, 2006).

SFGSs are usually observed near standing ope n water, including ponds, lakes, marshes, slow-moving streams, and sloughs; however, th ey are also observed at temporary pools including stock ponds, channelized sloughs, and reservoirs (U SFWS, 1985 and 2007; NatureServe, 2007; Kaplan, 2002; and Goals Pr oject, 2000). It is speculated that SFGS remain close to open water to retain proximity to anuran species, their preferred prey (USFWS, 2006). These snakes avoid brackish water because their preferred prey, the CRLF, cannot survive in saline water (USFWS, 2007). In addition, Pa cific tree frogs and

their larvae cannot survive in water with a salinity of 7.0 ppt or greater (USFWS, 2006). However, SFGS may use ditches influenced by the tides as “migration corridors between

disconnected areas of freshwater we tland habitat” (Powers, 2003).

Shallow water near the shoreline is required fr om May to July, to allow the anuran prey to hatch and metamorphose (USFWS, 2006); SFGSs are unable to capture their prey effectively in water that is more than 5 cm deep (USFWS, 2006). Shallow water also exposes rocks, algal mats, and floating vegetation found around the edges of the pond which the SFGSs use as basking sites (USFWS , 2006). These sites may also be used by the anurans and allows the SFGS greater access to their prey (USFWS, 2006).

3SFGS prefer emergent vegetation, including catt ails, bulrushes, spike rushes, and water plantain, for cover (USFWS, 1985 and 2007); howe ver, they will also seek cover in the water if necessary (USFWS, 1985). If these ty pes of vegetation are not available, SFGSs can be found in aquatic areas surrounded by willow trees as long as there is only a small distance between the overhanging vegetation and the ground (USFWS, 2006). SFGSs sun themselves at the edges of ponds or st reams and will also use the area between the aquatic habitat required for their prey and th e grasslands where they aestivate (become inactive or dormant) for basking (USFWS, 1985).

Upland grassy hillsides near ponds are also used for basking (USF WS, 1985). It is thought that SFGS may prefer hillsides that f ace south or west because they receive more sun (USFWS, 2006). Coyote bush, wild oat, w ild barley, and other brome species may be found in the SFGS’s upland habitat (USF WS, 2006). SFGS “prefer a grassland/shrub matrix with brush densities ranging from 1 averaged sized bush/30 square meters to 1 large bush/20 square meters” (USFWS, 2006) . This mix provides both cover from predators and also exposed surfaces to allow the SFGS sun themselves, an important part of their thermoregulat ion (USFWS, 2006). The preferred brush to grassland ratios are maintained or can be achieved by allowing livestock grazing (USFWS, 2006). Large SFGS populations have been found to coincide w ith areas of land that are used for cattle grazing (USFWS, 2006). Gopher activity, whic h moves nitrogen-poor subsoil to the surface, has also been shown to stimulate ear ly successional conditi ons (open grassland) required by the SFGS (USFWS, 2006). Alt hough grazing appears to have a positive impact on the SFGS, overgrazing can be detrim ental to this species as SFGS habitat may no longer be useful if the vegetative cover falls below 20 cm (USFWS, 2006).

Rodent burrows and thick grass mats near th e ponds are used for shelter and aestivation when the ponds become dry (USFWS, 1985 a nd 2007 and NatureServe, 2007). SFGSs may also forage for amphibians in the rodent burrows during the summer (Goals Project, 2000). These burrows are also used for hi bernation, since SFGSs found along the coast will hibernate during the winter (USFWS, 2006 and 2007). However, SFGS have been observed emerging from their burrows to bask in the winter indicat ing that SFGS may not truly hibernate (USFWS, 2006). This could also be due to the relativ ely warm climate of the San Francisco Bay area (USFWS, 2006). SFGSs that are farther inland are more likely to be active year-round (USFWS, 2007).

Recapture studies have indicat ed that SFGS have small home ranges that are determined by the availability of food a nd cover (USFWS, 1985). Most individuals remain within

one or two hundred meters of their aquatic and upland habitats (USFWS, 2006). However, some snakes may be able to travel up to two km or more in a short period of time (Goals Project, 2000). Although SFGS typically do not tr avel far, they may follow their prey to new areas (USFWS , 2006). It is in pursuit of their prey that SFGS may be adversely affected by creek channelizati on, removal of vegetation, and other flood control measures that are sometimes impl emented in riparian areas (USFWS, 2006). Garter snakes are typically found from sea level to 2400 m (8000 feet) (Morey, 2005).

41.5. Life History and Reproduction

SFGSs mate in the spring (March and Apr il) and fall (September through November); however, mating is “concentrated in the first few warm da ys of March” (USFWS, 1985 and 2006 and Goals Project, 2000). The increase d mating in the spring is correlated with SFGSs emerging from their burrows and c ongregating at the aquatic feeding areas (USFWS, 2006). Aggregations of mating adu lt SFGSs have also been observed on open grassy slopes on warm sunny mornings in la te October and early November (USFWS, 1985). It is thought that the female’s role in mating is re latively passive. Females release pheromones to attract males, males actively seek out the females primarily using scent, and several males may court the same female simultaneously. These types of behaviors have been identified in other subspecies of the common garter snake (USFWS, 1985 and SF Zoo). Female SFGS can store the male’s sperm over the winter and can retain viable sperm for periods ranging from 3 to 53 months (USFWS, 1985 and Goals Project, 2000).

Ovulation in the common garter snake typica lly occurs in late spring with pregnancy resulting in early summer (USFWS, 1985). The young are typically born about three to

four months after successf ul mating (Woodland Park Zoo) . SFGS are ovoviviparous meaning that the eggs hatch within th e female’s body and the young are born live (USFWS, 1985 and SF Zoo). Female SFGSs give birth from June through September with young typically born in July or A ugust (USFWS, 2007; NatureServe, 2007; and Goals Project, 2000). However, young can be bo rn as late as early September (Goals Project, 2000). The number of young can range from three to 85 but are more typically in the range of 12 to 24 (USFWS, 1985) . Most often around 16 young are produced (USFWS, 2007; SF Zoo; and Goals Project, 2000).

The young are typically born in the upland areas near the aquatic feeding habitats. Neonate snakes are 18 to 20 cm in length a nd disperse immediately after they are born (Woodland Park Zoo and Goals Project, 2000). Juvenile SFGS grow quickly during their first year and spend most of their time feed ing (Goals Project, 2000). These snakes are typically considered to be ma ture at two years of age when the males are about 46 cm and the females are about 55 cm; however, some sn akes take longer to mature and may not reach maturity until they are three year s old (Woodland Park Zoo and Goals Project, 2000).

1.6 Diet

Newborn and juvenile SFGS prey almost ex clusively on Pacific tree frogs in temporary pools during the spring and early summer (USFWS, 2006 and 2007). Juvenile SFGS may capture metamorphosed Pacific tree fr ogs in upland habitats; however, they primarily feed on the newly metamorphosed frogs once the temporar y pools begin to dry up and the frogs begin to disperse (USFWS, 2006). A laboratory experiment performed using juvenile SFGS showed that Pacific tree frogs elicited the highe st response rate out of all of the common prey items that were tested (USFWS, 2006). Observations at one SFGS site have shown that anuran numbers decreased during dry years with a subsequent decrease in the survival of SFGS juvenile s (USFWS, 2006). This observation indicates

5that the SFGS may be so dependent on their a nuran prey that they are not able to switch to other available prey sources if nece ssary to survive (USFWS, 2006). SFGS under 500 mm snout-to-vent length (SVL) require Paci fic tree frogs in various stages of metamorphosis, whereas individuals over 500 mm SVL can consume Pacific tree frog, CRLF, and bullfrog tadpoles and adults (USFWS, 2006).

The main diet of adult SFGS consists of CRL F, which are listed as a threatened species (USFWS, 1985 and 2007). Adult SFGSs consum e CRLFs in the late summer when they metamorphose (USFWS, 2006). The emergence of the CRLF in the late summer allows the adult SFGS to continue feeding after th e Pacific tree frogs have left the drying wetland areas (USFWS, 2006). This observed be havior likely explai ns the high activity level of SFGSs in the late summer (USF WS, 2006). Adult SFGSs may also feed on juvenile non-native bullfrogs ( Rana catesbeiana ), but are unable to consume the larger adults (USFWS, 2007). Bullfrogs are known to be found in degr aded habitats and it is thought that bullfrogs may allow SFGS to col onize areas where Pacific tree frogs or CRLF cannot exist (USFWS, 2006). Although bullfrogs may be consumed by SFGSs, captive SFGS often regurgitate th em indicating that they ma y be undigestable, and that bullfrogs may not be consumed by w ild SFGS populations (USFWS, 2006).

Immature California newts ( Taricha torosa ), California toads ( Bufo boreas halophilus ) recently metamorphosed western toads ( Bufo boreas ), threespine stickleback ( Gasterosteus aculeatus ), and non-native mosquito fish ( Gambusia affinis ) are also known to be consumed by SFGS (USFWS, 1985). SFGS are one of the few animals

known to eat the California newt without su ffering the toxic effects of this organism (USFWS, 2007). Small mammals, reptiles, am phibians, possibly inve rtebrates, and some fish species may also be consumed by the SFGS if they can be captured in shallow water (USFWS, 1985 and 2006). Captive SFGS have been found to consume earthworms; however, some individuals will starve instead of eating them (USFWS, 2006). Earthworms may also not be readily availabl e in the wild, further indicating that wild populations of SFGS may not prey on these animals (USFWS, 2006).

1.7 References

Goals Project. 2000. Baylands Ecosystem Species and Community Profiles: Life histories and environmental requirements of key plants , fish and wildlife. Prepared by the San Francisco Bay Area Wetlands Ecosystem Goals Project. P.R. Olofson, editor. San Francisco Bay Regional Water Quality Contro l Board, Oakland, California. Available

online at: http://sfep.abag.ca.gov/pdf/speciescommunity/Species_and_Comm unity_Profiles%5BPart3%5D.pdf (Accessed on November 5, 2007).

Kaplan, M. 2002. Not-so-common garters. Meli ssa Kaplan’s Herp Care Collection. Last updated April 19, 2007. Available online at: http://www.anapsid.org/garters.html (Accessed on October 16, 2007).

6Morey, S. 2005. R061-Common Garter Snake. California Wildlife Habitat Relationships System, a database of the California Depa rtment of Fish and Game (CDFG), in cooperation with the California Interagency Wildlife Task Group. Database version 8.1.

Available online at: nrm.dfg.ca.gov/FileHandler.a shx?DocumentVersionID=2814 (Accessed on November 5, 2007).

NatureServe. 2007. NatureServe Explorer: An online encyclopedia of life [web application]. Version 6.2. NatureServe, Arlington, Virginia. Available online at: http://www.natureserve.org/explorer/servl et/NatureServe?searchName=Thamnophis+sirt

alis+tetrataenia . (Accessed: October 15, 2007).

Powers, D.J., and Associates, Inc. 2003. Envi ronmental Constraints Analysis for the San Bruno Grade Separation Project (MP 10.8 to 12.0). Available online at: http://www.caltrain.org/pdf/SB_L.pdf (Accessed on October 25, 2007).

San Francisco Planning Department. 2001. Pe ninsula Watershed Management Plan – Final Environmental Impact Report (EIR). EIR Certification Date: January 11, 2001.

Available online at: http://sfwater.org/Files/Reports/3-Env_Set_Impacts.pdf (Accessed on November 5, 2007).

SF Zoo website. Available online at: http://www.sfzoo.org/openrosters/Vie wOrgPageLink.asp?LinkKey=13516&orgkey=182

1 (Accessed on November 2, 2007).

U.S. Fish and Wildlife Service (USFWS). 1967. Native Fish and Wildlife, Endangered Species (32 FR 4001). Washington, D.C.

USFWS. 1985. Recovery Plan for the San Francisco Garter Snake ( Thamnophis sirtalis

tetrataenia ). U.S. Fish and Wildlife Service, Portland, Oregon. 77 pp. Available online

at: http://ecos.fws.gov/docs/recovery_plan/850911.pdf (Accessed on October 16, 2007)

USFWS. 2005. San Francisco garter snake returns to its namesake city. June 2005.

Available online at: http://www.fws.gov/sacramento/ea/feature_stories/SFGS_returns_mediaevent.htm (Accessed on October 16, 2007).

USFWS. 2006. 5-Year Review: Summary and Evaluation for the San Francisco Garter Snake ( Thamnophis sirtalis tetrataenia ). U.S. Fish and Wildlife Service, Sacramento Field Office, Sacramento, Califor nia. 42 pp. Available online at: http://www.fws.gov/sacramento/es/docume nts/San%20Francisco%20Garter%20Snake% 205%20Year%20Review.FINAL.pdf (Accessed on October 25, 2007 )

USFWS. 2007. Species Account: San Francisco Garter Snake ( Thamnophis sirtalis

tetrataenia ). Sacramento Fish and Wildlife Office. Available online at:

78 http://www.fws.gov/sacramento/es/animal_spp_acct/sf_garter_snake.pdf (Accessed on October 16, 2007).

Woodland Park Zoo website. Available online at: http://www.zoo.org/factsheets/garter_s nake/sanFransiscoGarterSnake.html# (Accessed on November 5, 2007).