Some turtles survive freezing winters underwater by breathing through their cloaca—essentially their rear end.

This survival strategy is primarily observed in North American species like the painted turtle (Chrysemys picta) and the wood turtle. During winter, these reptiles enter bradymetabolism, a state of extreme metabolic suppression where their heart rate drops to just one to five beats per minute. This dramatic slowdown allows them to survive in near-freezing water with minimal energy expenditure.Cloacal respiration works through the cloaca, a heavily vascularized opening used for excretion and reproduction. The dense network of blood vessels in this area extracts dissolved oxygen directly from the surrounding water—a mechanism similar to how fish use gills, though far less efficient and only viable because the turtle is in a dormant state.Research by biologists including Dr. Jacqueline Litzgus has demonstrated that these turtles can remain fully submerged for over 100 days without breathing atmospheric air. To prevent dangerous lactic acid buildup in their tissues during this extended period, turtles draw calcium from their own shells to neutralize the acid. This sophisticated survival strategy enables them to thrive in northern climates where lakes remain frozen for several months each year.