Thamnophis sirtalis pop. 1

South Coast Gartersnake

Family: Colubridae · Class: Reptilia · Order: Squamata

Conservation status: G5T1T2 S1S2

The South Coast Gartersnake (Thamnophis sirtalis pop. 1) is a distinct population of the common garter snake endemic to the coastal regions of southern California. This subspecies exhibits the typical garter snake body plan, with adults measuring 46 to 102 centimeters (18 to 40 inches) in total length. The species displays three longitudinal stripes running the length of the body: a prominent yellow or cream dorsal stripe and two lateral stripes, with the ground color between stripes typically dark brown to black with red markings. Historically, this population ranged along the southern California coastal plain from the Santa Clara River Valley in Ventura County south through Los Angeles County to northwestern Orange County. According to NatureServe, the species has disappeared from approximately 75% of its historical range, with current distribution limited to scattered localities. Remaining populations are documented in areas including the Santa Clara River Valley, parts of Los Angeles County, and isolated coastal locations. The South Coast Gartersnake inhabits a variety of wetland and riparian habitats within the coastal plain ecosystem. Primary habitat includes freshwater marshes, seasonal pools, streams, and their adjacent upland areas. The species requires permanent or semi-permanent water sources for foraging and breeding, while utilizing nearby terrestrial areas for thermoregulation and shelter. Urban development has eliminated much of the historical wetland habitat throughout the species' range. This semi-aquatic snake feeds primarily on amphibians, particularly frogs and tadpoles, supplemented by fish, earthworms, and occasionally small mammals. Individuals are active during daylight hours, particularly in morning and late afternoon when temperatures are moderate. Mating occurs in spring following emergence from winter dormancy, with females giving birth to live young in late summer. Litter sizes typically range from 10 to 40 offspring, depending on female size and condition. The South Coast Gartersnake receives a NatureServe global rank of G5T1T2, indicating the overall species is secure but this particular population is critically imperiled to imperiled. California Department of Fish and Wildlife classifies Thamnophis sirtalis in the southern part of its California range as a Priority 1 Species of Special Concern. The primary threat to this population is habitat loss and fragmentation due to urban and agricultural development throughout the coastal plain. Remaining populations face additional pressures from water diversions, pollution, introduced predators, and habitat degradation. Conservation efforts focus on protecting existing wetland remnants and restoring connectivity between isolated populations. The dramatic range reduction and continuing habitat pressures make this one of California's most vulnerable reptile populations, requiring immediate conservation attention to prevent further population decline and potential extirpation.

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, and more.