We see many types of turtles roaming around northwest Iowa in the summertime, especially painted turtles and snapping turtles.
But we don't see any in the winter.
Where do they all go?
Painted turtles and snapping turtles spend their winters in lakes or ponds, living beneath the ice the forms. They survive because of a variety of adaptations.
Turtle metabolism slows down in cold water.
Turtles are reptiles and are ectotherms, or cold-blooded. Their body temperature adjusts to their surroundings.
In freezing cold water, a turtle's body temperatures drops to match it, and with it drops its metabolism. In fact, a turtle's metabolism slows by as much a 99 percent, allowing it to survive without food or oxygen for up to 100 days.
Turtles spend the winter in water.
Turtles overwinter in the water and not on land, because the water temperature stays consistent. Air temperature fluctuates, and sometimes it can actually get too cold for turtles to survive. The water actually protects them.
Unlike frogs, turtles cannot survive having ice crystals in their bodies.
Turtles can absorb oxygen.
Normally, turtles breathe oxygen just like humans, into their lungs. However, when surviving the winter underwater, they cannot breathe oxygen in the same way.
Instead, oxygen is absorbed from the water as it passes over parts of the body that are filled with blood vessels, including the skin, mouth and cloaca, or the hind end.
Turtles can survive in low-oxygen environments.
As winter continues, fish and other creatures under the ice begin to use up a lot of the oxygen in the water. It becomes a hypoxic --- low oxygen --- or anoxic --- no oxygen environment.
However, painted and snapping turtles can switch up their metabolism to one that doesn't need oxygen. This does build up acid in their bodies that can damage tissue over time. Painted turtles in particular can use calcium from their shells to neutralize that acid, though.
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