Where have the turtles gone?
The turtles don’t go anywhere, but rather hide and relax through Brumation! Brumation is very similar to hibernation but done by ectotherms (cold-blooded animals) and involves specific metabolic processes. Generally, turtles find a specific site, called hibernacula, to rest. Hibernacula are very specifically chosen, and dependent on species and life stage. In northern parts of North America, like here in Canada, turtle can spend almost half their life in an overwintering state in their hibernacula, and thus have specific adaptions!
The Midland Painted Turtle
The widespread and most common turtle, the midland painted turtle is an anoxia tolerant species ( meaning it can withstand the depletion of oxygen,) that prefer shallow vegetated water where they bury themselves in the mud. They are unique, in that hatchlings may spend the winter underground in their nest by freezing, where up to 50% of their body water freezes in extracellular space.
The Snapping TurtleSnapping turtles are the most likely to exhibit movement during winter. The anoxia tolerant Snapping turtle, adult and hatchlings alike, prefers hibernacula in very shallow water, in mud, where they can easily come up to breather during ice thaws. Hibernacula are often near burrows or lodges of muskrats and beavers. They appear to be the best at withstanding the cold and are found the farthest north of any aquatic (non-marine) turtle in North America.
The Blanding’s TurtleThe elusive Blanding’s turtle has similar hibernacula selection to snappers and painted turtles and is believed to be anoxia tolerant. Blanding’s turtles are more likely to be in stream tributaries, as it may not be as anoxia tolerant as the above two. More research is required on the species, especially what the hatchlings do.
The Northern Map Turtle
The northern map turtle is not anoxia tolerant, thus they require moving water that had dissolved oxygen. Therefore their hibernacula are normally in rivers and lakes, not ponds. Furthermore, they show preferences for sites near dams. They don’t bury themselves in the mud, but are rather just rest on the bottom rocks. Like the snapping turtle, they can exhibit some movement. Like the Blanding’s turtle, they require more research!
How do they do it?
Turtles breathe air, so how do they do it? Some turtle, like the midland painted turtle have a special adaption, where they breathe through their butt! Not exactly, but they use their cloaca. The Cloaca is an opening in a turtle's rear end where the rectum and urinary systems empty. By flexing the cloaca muscles, water goes in and out. Oxygen moving across this skin can be absorbed into one of the many blood vessels there! However this only works if there is dissolvedoxygen in the water!
During winter, Turtles also decrease in activity and their metabolism, by up to 90%, so that they don’t have to breathe as much in the first place. (Think of how much more we have to breathe when running then when sitting still. ) They will then “breath” anaerobically using stored fats causing a lactate accumulation (similar to how humans can have a buildup of lactic acid while running causing cramps). They have a special adaption where they use mobilizing cabonate buffers from their skeleton to neutralize the lactic acid and allows their bones to act as a respiratory for neutralized lactate.
The combination of these adaptions allows turtles to find hibernacula out of the water column where there is less dissolved oxygen, so that they can avoid predation during winter. However there is a trade-off. As the turtle is lethargic, from the cold and lactic accumulation, they are at a risk of predation in spring when they first emerge. To help with this, turtles in spring will try and warm up as quickly as possible by basking in the sun! Therefore in spring you can look forward to seeing an abundance of turtles out!
Packard, G. C., & Packard, M. J. (2001). The Overwintering Strategy of Hatchling Painted Turtles, or How to Survive in the Cold without Freezing: Neonatal turtles, like many cold-tolerant insects, exploit a capacity for supercooling to withstand exposure to subzero temperatures. AIBS Bulletin, 51(3), 199-207.
Rollinson, N., Tattersall, G. J., & Brooks, R. J. (2008). Overwintering habitats of a northern population of Painted Turtles (Chrysemys picta): winter temperature selection and dissolved oxygen concentrations. Journal of Herpetology, 42(2), 312-321.
Ultsch, G. R. (2006). The ecology of overwintering among turtles: where turtles overwinter and its consequences. Biological reviews, 81(3), 339-367.