20 dec 2009 Cold Snake Cloaca... A question that needs an answer

[Deb]

CNAH RESEARCH REQUEST Number 182
The Center for North American Herpetology The Plantation St. George Island, Florida http://www.cnah.org
29 December 2009

SNAKES UNDER ICE

My students recently observed Common Garter Snakes (Thamnophis sirtalis) overwintering underwater below ice. On 15 December 2009 and again on 17 December 2009, they brought me two different Common Garter Snakes, both of which were taken from an iced- over pond. The pond was 80-85 per cent frozen, and the snakes were taken from the water near the edge of the ice. The first one warmed in my hands, began moving, and was placed in a terrarium in my classroom. By the afternoon, it was striking and was as quite active. I eventually put the first snake in a refrigerator to get its body temperature to ca. 40 degrees F, and then released it when the outside temperatures were 40+ degrees F. The second serpent was returned immediately to the pond.

Can a Common Garter Snake diffuse oxygen through its cloaca, as can some turtles?

Any information on this phenomenon in snakes would be much appreciated. I can be contacted at

ssharp@usd232.org

Scott Sharp
Unified School District 232
Lawrence, Kansas

[crinaustin]

While most aquatic turtles overwinter while continually submerged (see http://www.flattenedpenny.com/corhs/...quatics_06.pdf), fully aquatic snakes like water and crayfish snakes typically overwinter in dens on land.

Hibernating reptiles slow their heartrates to as low as 2 beats per minute and their metabolic demands are minimal under these conditions.

Many reptiles such as stinkpots and garter snakes are active and can be pretty alert at temperatures just above freezing. I've see alert garter snakes out in the forties in Vermont during February when most water bodies are frozen. Many chorus frogs breed in the winter when water temperatures are in the thirties and air temperatures may be below freezing. Low temperatures don't necessarily require hibernation in herps.

Pharyngeal and cloacal breathing is a strategy used by aquatic turtles to avoid visiting the surface to breathe. The best species at this are the musk and mud turtles, and loggerhead musks can survive underwater indefinitely if it's well oxygenated. Sliders and cooters typically have to breathe air around every two hours under normal metabolic conditions at active temperatures or they drown.

You don't mention if the garter snakes were found moving around or actually in the icy water. I'd be surprised if they could survive over winter under water like a slider or cooter. The problem seems to be that aquatic turtles probably can allow water into their lungs and survive by expelling it later while snakes typically drown when this happens. If the snakes were inactive out in the open, I suspect they were caught out by an unexpected cold snap.

CR