How do painted turtle hatchlings “defrost back to life”?

Painted turtles are resilient denizens of northern North America. Born in autumn, these tiny creatures enter a state of suspended animation within their shallow, underground nests. As winter approaches, “their hearts have stopped beating,” Sir David Attenborough narrates in this clip from Frozen Planet II, “and only their brains have remained active, and even then, only very faintly.”

This overwintering adaptation, a unique marvel of nature, relies on a process called supercooling. Here, the hatchlings’ bodily fluids fall below their freezing point without freezing solid. This extraordinary ability allows them to wait out winter, staying in a state of frozen animation until warmer temperatures trigger their dormant bodies.

“Slowly, they return to life” as spring takes hold, emerging when food resources are increasingly available. The Wildlife in Winter Project shares additional details about painted turtle hatchlings and adults:

“Like hibernation in mammals, brumation is a physiological response to cold conditions that conserves energy and allows an animal to survive until warm weather returns. Mammals are warm-blooded (endotherms) and reduce their body temperature during hibernation.

“Painted turtles, like all reptiles, are cold-blooded (ectotherms), so their body temperature matches the surroundings. They can reduce their metabolism by 99% in near-freezing water and survive without food or oxygen for 100 days…”

Winter water below its frozen surface can stay above freezing, protecting the adult painted turtles from the extreme cold air above. If the water temperatures drop, the adult turtles won’t survive ice crystals forming in their body tissues. Hatchling painted turtles,” Wildlife in Winter continues, “are the exception to the ‘No Ice’ rule.”

“After hatching in the fall, young painted turtles remain in their underground nest all winter. These nests are well above the frost line and experience cold temperatures for months. The overwintering baby turtles have fat reserves that provide the energy needed to remain underground from late summer until spring without eating. In response to subfreezing temperatures, newly hatched turtles produce higher levels of glucose and glycerol, which may function as a form of antifreeze. One study found hatchling turtles survived with more than 50% of their body water as ice.”

Watch these overwintering videos next:
• Return of the Wood Frog – Invisible Nature
• L’orchestre d’hibernation animaux and how animals hibernate
• What’s the difference between hibernation and sleep?
• Where Do Birds Go In Winter?
• How do trees survive winter?