thumbnail

A preliminary investigation of the variables affecting the distribution of giant gartersnakes (Thamnophis gigas) in the Sacramento Valley, California

Open-File Report 2015-1178
Prepared in cooperation with the California Department of Water Resources
By: , , , and 
https://doi.org/10.3133/ofr20151178

Links

Abstract

Giant gartersnakes (Thamnophis gigas) comprise a species of rare, semi-aquatic snake precinctive to the Central Valley of California. Because of the loss of more than 90% of their natural habitat, giant gartersnakes are listed as Threatened by the United States and California endangered species acts. Little is known, however, about the distribution of giant gartersnakes in the Sacramento Valley, which is where most extant populations occur. We conducted detection-nondetection surveys for giant gartersnakes throughout the rice-growing regions of the Sacramento Valley, and used occupancy models to examine evidence for the effects of landscape-scale GIS-derived variables, local habitat and vegetation composition, and prey communities on patterns of giant gartersnake occurrence. Although our results are based on a relatively small sample of sites, we found that distance to historic marsh, relative fish count, and an interaction of distance to historic marsh with proportion of habitat composed of submerged vegetation were important variables for explaining occupancy of giant gartersnakes. In particular, giant gartersnakes were more likely to occur closer to historic marsh and where relatively fewer fish were captured in traps. At locations in or near historic marsh, giant gartersnakes were more likely to occur in areas with less submerged vegetation, but this relationship was reversed (and more uncertain) at sites distant from historic marsh. Additional research with a larger sample of sites would further elucidate the distribution of giant gartersnakes in the Sacramento Valley.

Suggested Citation

Halstead, B.J., Skalos, S.M., Casazza, M.L., and Wylie, G.D., 2015, A preliminary investigation of the variables affecting the distribution of giant gartersnakes (Thamnophis gigas) in the Sacramento Valley, California: U.S. Geological Survey Open-File Report 2015-1178, 34 p., http://dx.doi.org/10.3133/ofr20151178.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Introduction
  • Giant Gartersnake Occupancy Rates in Sacramento Valley
  • Summary
  • References Cited
  • Glossary
Publication type Report
Publication Subtype USGS Numbered Series
Title A preliminary investigation of the variables affecting the distribution of giant gartersnakes (Thamnophis gigas) in the Sacramento Valley, California
Series title Open-File Report
Series number 2015-1178
DOI 10.3133/ofr20151178
Year Published 2015
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Western Ecological Research Center
Description vi, 34 p.
Time Range Start 2011-01-01
Time Range End 2012-12-31
Country United States
State California
Other Geospatial Sacramento Valley
Online Only (Y/N) Y
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details