Several invasive pests, including red swamp crayfish, American bullfrogs and nutria rodents, can now be found in the Sacramento-San Joaquin River Delta. At the same time, native snakes that feed on these species are struggling. Some are classified as threatened and their populations are continuing to decline, making further study of their behaviors essential. This project investigated the relative abundance, habitat use and diet of snakes at two sites in the Delta, Staten Island Preserve and a wetland in Clarksburg privately owned by Tom and Laura Uslan.
Surveys revealed that valley garter snakes (Thamnophis sirtalis fitchi) are the dominant garter snake species. They prefer to live in dens along the irrigation canals of rice fields as opposed to other crops. They were found in high abundance in canals with emergent vegetation that they could use for cover and protection from avian predators. Interestingly, capture locations suggest that female garter snakes stay closer to dens, whereas males tend to travel, perhaps in search of female mates. For protected garter snake species like the federally endangered giant garter snakes, this suggests efforts should be made to protect female dens.
Stomach contents from manually palpated garter snakes showcased a preference for American bullfrogs (Lithosbates catesbeianus), an invasive species in the Sacramento-San Joaquin River Delta.
Additionally, the study documented a previously undiscovered behavior by the snakes while underwater: rebreathing air from air bubbles on their nares, coined “narial bubbles,” that are analogous to a natural form of scuba gear seen in semi-aquatic lizards, spiders and beetles.