Behavioral response of giant gartersnakes (Thamnophis gigas) to the relative availability of aquatic habitat on the landscape

Abstract

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...

Integrating growth and capture–mark–recapture models reveals size‐dependent survival in an elusive species

“…Our apparent survival estimate, /, is the product of true survival, S, and the probability that an individual does not permanently emigrate from the site. We could potentially improve our estimates of emigration and survival by using auxiliary data on the movement and survival of giant gartersnakes from radio-telemetry studies (Halstead et al 2012, Reyes et al 2017 to inform the probability that an individual moves off of the sample array (using a model similar to Powell et al 2000). Large, adult giant gartersnakes exhibit site fidelity, with small home ranges that overlap between years for most individuals (Reyes et al 2017).…”

“…We could potentially improve our estimates of emigration and survival by using auxiliary data on the movement and survival of giant gartersnakes from radio-telemetry studies (Halstead et al 2012, Reyes et al 2017 to inform the probability that an individual moves off of the sample array (using a model similar to Powell et al 2000). Large, adult giant gartersnakes exhibit site fidelity, with small home ranges that overlap between years for most individuals (Reyes et al 2017). The site fidelity of radio-tracked giant gartersnakes suggests that permanent emigration might not have had a large effect on our estimates of apparent survival for large, adult snakes.…”

A tale of two valleys: endangered species policy and the fate of the giant gartersnake

“…In contrast to the conversion of wetlands to orchards and row crops in the San Joaquin Valley, in the Sacramento Valley a mosaic of remnant historical tule marshes (Halstead et al 2014(Halstead et al , 2016, constructed marshes for waterfowl hunting (Frayer et al 1989;Reyes et al 2017), and widespread rice agriculture and associated water delivery and drainage canals (Hansen and Brode 1980;Halstead et al 2010;Reyes et al 2017) continue to support populations of giant gartersnakes. Rice agriculture acts as surrogate marsh habitat and, in addition to tule marshes, is also used for waterfowl hunting, which may further protect rice from conversion to other types of agriculture unsuitable for giant gartersnakes.…”

“…For example, optimizing the design and management of giant gartersnake habitat restoration projects remains an important unknown in giant gartersnake recovery. Although much has been learned in the past decade about giant gartersnake habitat selection (Valcarcel 2011;Halstead et al 2016;Reyes et al 2017), formal evaluation of giant gartersnake colonization and use of restored wetlands is incomplete. Optimum ratios of aquatic active season and terrestrial brumation habitat remain unknown, as does habitat selection of male, neonate, and juvenile snakes that are too small for current radio telemetry methods.…”

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“…In contrast to the conversion of wetlands to orchards and row crops in the San Joaquin Valley, in the Sacramento Valley a mosaic of remnant historical tule marshes (Halstead et al 2014(Halstead et al , 2016, constructed marshes for waterfowl hunting (Frayer et al 1989;Reyes et al 2017), and widespread rice agriculture and associated water delivery and drainage canals (Hansen and Brode 1980;Halstead et al 2010;Reyes et al 2017) continue to support populations of giant gartersnakes. Rice agriculture acts as surrogate marsh habitat and, in addition to tule marshes, is also used for waterfowl hunting, which may further protect rice from conversion to other types of agriculture unsuitable for giant gartersnakes.…”