Movements and habitat use in gravid and nongravid female garter snakes (Colubridae: Thamnophis)



We examined movements and habitat use with respect to reproductive condition for female garter snakes (Thamnophis sirtalis and T. elegans) in south-eastern British Columbia, Canada. Radiotelemetry was used to measure movements by snakes and the locations of animals were used as habitat sampling points to examine patterns of habitat use. Rates of movement of gravid females were low during gestation, but increased following parturition until they were similar to those of nongravid females. Both groups used areas characterized by high levels of cover (vegetation, rocks, or trees), but there were marked differences in the habitat features of the sites selected. Gravid females remained primarily in rocky areas that were relatively rare on the study site. In contrast, nongravid females used a variety of habitats, ranging from grasslands to forests, but preferred areas with relatively high amounts of overhead cover. Our results indicate that predator avoidance may be a primary feature of habitat choice for both groups. However, gravid females appear to have an additional requirement for careful thermoregulation, and may be selecting sites that balance both needs.