For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit https://www.usgs.gov/ or call 1-888-ASK-USGS (1-888-275-8747).For an overview of USGS information products, including maps, imagery, and publications, visit https:/store.usgs.gov.Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.Suggested citation: Reyes, G.A., Halstead, B.J., Rose, J.P., Ersan, J.S.M., Jordan, A.C., Essert, A.M., Fouts, K.J., Fulton, A.M., Gustafson, K.B., Wack, R.F., Wylie, G.D., and Casazza, M.L., 2017, Behavioral response of giant gartersnakes (Thamnophis gigas) to the relative availability of aquatic habitat on the landscape: U.S. Geological Survey OpenFile Report 2017-1141, 134 p., https://doi.org/10.3133/ofr20171141. ISSN 2331ISSN -1258 Table 8. Probability of giant gartersnakes (Thamnophis gigas) moving more than 100 meters, based on proportion of rice within 100 meters of the snake's location, and a third order polynomial of Julian date ......... 28 Table 9. Regression coefficient estimates for average movement rates (log meters per day) of giant gartersnakes (Thamnophis gigas), based on proportion of rice within 100 meters of the snake's location, AbstractMost extant giant gartersnake (Thamnophis gigas) populations persist in an agro-ecosystem dominated by rice, which serves as a surrogate to the expansive marshes lost to flood control projects and development of the Great Central Valley of California. Knowledge of how giant gartersnakes use the rice agricultural landscape, including how they respond to fallowing, idling, or crop rotations, would greatly benefit conservation of giant gartersnakes by informing more snake-friendly land and water management practices. We studied adult giant gartersnakes at 11 sites in the rice-growing regions of the Sacramento Valley during an extended drought in California to evaluate their response to differences in water availability at the site and individual levels. Although our study indicated that giant gartersnakes make little use of rice fields themselves, and avoid cultivated rice relative to its availability on the landscape, rice is a crucial component of the modern landscape for giant gartersnakes. Giant gartersnakes are strongly associated with the canals that supply water to and drain water from rice fields; these canals provide much more stable habitat than rice fields because they maintain water longer and support marsh-like conditions for most of the giant gartersnake active season. Nonetheless, our results suggest that maintaining canals without neighboring rice fields would be detrimental to giant gartersnake populations, with decreases in giant gartersnake survival rates ass...

Many imperiled species face increasing extinction risk that requires interventional management like translocation or captive rearing. The use of translocations to successfully restore or create populations requires that animals survive at recipient sites, information that is often lacking for imperiled species and that can be risky to acquire if not obtained before a species has dwindled in number. The giant gartersnake (Thamnophis gigas), a semiaquatic snake endemic to the Central Valley in California, USA, has declined after losing >90% of its historical habitat and may benefit from successful translocations to protected habitat. We released adult and captive‐reared juvenile snakes from 2 donor sites into a recently restored wetland in 2019 and 2020 and compared their survival, movement, and activity using radio‐telemetry through 2021. We monitored juvenile survival for 2 years in captivity after birth and then estimated post‐release survival at the recipient site using radio‐telemetry. Just 8% of translocated adult snakes survived >801 days (95% CI = 1–64%) compared with 39% of resident snakes at the donor sites surviving >1,154 days (95% CI = 23–68%). This equated to annualized survival rates of translocated adults (x¯ $\bar{x}$ = 0.32, 95% CI = 0.12–0.82) that were roughly half that of resident snakes (x¯ $\bar{x}$ = 0.74, 95% CI = 0.63–0.89). Translocation was negatively correlated with survival, but movement and activity received little support in models. Seventy‐six percent of juvenile snakes survived captivity and, once released, juvenile survival was 60% (95% CI = 38–94%) for the 4‐month monitoring period before winter. It is unclear why survival of translocated adult snakes was lower than that of resident snakes, but there was little evidence for differences in behavior (e.g., increased surface activity, average distance moved, emigration from the translocation site) that are commonly cited causes of mortality in other translocation studies. Our results suggest that, in the absence of a clear understanding as to what contributes to adult survival after release to a new site, future work using captive‐rearing and juvenile translocation may be more promising for establishing and recovering populations than just translocating adults given the high survival of juveniles.

By the mid-20th Century, giant gartersnakes (Thamnophis gigas) had lost more than 90% of their Central Valley marsh habitat and were extirpated from more than two-thirds of their range. This massive habitat loss led to their inclusion in the inaugural list of rare species under the California Endangered Species Act (CESA). Listing under the CESA provided giant gartersnakes legal protection and mechanisms for recovery, and subsequent listing under the U.S. Endangered Species Act (federal ESA) further fortified these protections. But how effective has listing under these endangered species acts (ESAs) been at achieving their goal of giant gartersnake recovery? Herein, we review relevant aspects of giant gartersnake ecology, illustrate how listing has benefited giant gartersnakes and what challenges have been faced in slowing declines and recovering populations, and chart a course toward improved conservation, management, and recovery of giant gartersnakes. Although listing as threatened under both state and federal ESAs has not yet achieved recovery of giant gartersnakes, the increased knowledge gained and mechanisms for protecting giant gartersnake habitat on private and public lands developed over the past 50 years has improved conservation of this endemic California snake.