Geomagnetic sensitivity and orientation in eastern garter snakes (Thamnophis sirtalis)

Douglas Eliot Smith, University of Rhode Island


Thirteen eastern garter snakes (Thamnophis sirtalis) were each kept in a terrarium for 10 to 15 days inside a solenoid made of electrical wire and attached to a DC power source. When activated, the solenoid reduced the intensity and reversed the direction of the ambient magnetic field inside the aquarium. Food was placed in an L-shaped corridor attached to the aquarium before the solenoid was turned on. The time between activation of the solenoid and the first strike at the food was measured. Snakes that were exposed to the magnetic cue learned to associate it with the presence of food and were able to find the food faster than the control snakes. This suggested that T. sirtalis senses magnetic fields, although the mechanism used is unknown. Following the original observation, a 6-coil magnetic field generator calibrated to the ambient geomagnetic field was constructed. It created an area of near-zero magnetic intensity within an eight-foot diameter arena. Sixty snakes were each placed in the center of the arena for 30 trials before the coils were turned on to observe the compass bearing they took as they moved to the arena perimeter. I also recorded which way they turned upon reaching the perimeter. The same snakes were observed for 15 trials after the coils were activated and magnetic cues were eliminated in the arena. Snakes displaced 1.55–1.7 km from home ranges changed from southwest headings to random directional choice when the null-field was in place (X2 = 194.49; CV = 14.067; N = 1350). The tendency to turn counter-clockwise at the arena perimeter dropped from 92% to 52% and from 92% to 49% when the null-field was on in two separate sets of experiments. The reason for a magnetic bias in turning direction is unclear, but may have to do with maintaining a constant bearing that would lead a snake back to a primary shelter in a loop. The results of the second and third sets of experiments, involving 2700 trials, suggest that geomagnetism can be used by garter snakes for navigation locally and over relatively long distances. ^

Subject Area

Biology, Animal Physiology|Biology, Zoology

Recommended Citation

Douglas Eliot Smith, "Geomagnetic sensitivity and orientation in eastern garter snakes (Thamnophis sirtalis)" (2002). Dissertations and Master's Theses (Campus Access). Paper AAI3053123.