Do Turtles Hibernate? How Turtles Survive the Winter

Hibernation or brumation?

Turtles do not hibernate in quite the same way as bears or bats. Mammals are warm-blooded and keep their own body temperature high, so in hibernation they actively lower it. Turtles are cold-blooded, or ectothermic, which means their body temperature follows that of their surroundings, as explained in Are reptiles cold-blooded?

When autumn days get shorter and colder, a turtle’s body cools, its heart rate falls and its metabolism, the rate at which it uses energy, drops to a tiny fraction of its summer level. This winter dormancy in reptiles is usually called brumation. Many people still say turtles hibernate, and both words are used in everyday language.

In the northern United States, Canada and much of Europe, turtles typically brumate from about October or November until March or April. Farther south, many turtles stay partly active through winter and may come out to bask on warm days.

Where do pond turtles go in winter?

Most freshwater turtles spend the winter underwater. They settle on the bottom of a pond, lake or slow river, often burying themselves partly in soft mud or hiding under banks, logs and vegetation. Water is densest at about 4 °C (39 °F), so in a deep enough pond the bottom water stays a little above freezing even when the surface is frozen solid.

The common snapping turtle is one of the toughest winter survivors. It overwinters in ponds, marshes and rivers across its range, from southern Canada southward, and is sometimes seen moving slowly under clear ice. Snapping turtles often choose spots where some oxygen remains in the water. More about their habitat is in Where do snapping turtles live?

How do turtles breathe under the ice?

A turtle under the ice cannot come up for air for months. It survives in two ways.

Breathing without lungs. At low temperatures a turtle needs very little oxygen. Some species can absorb part of what they need directly from the water through their skin and through the lining of the cloaca, the rear opening of the body. This is sometimes called cloacal or “butt” breathing. It works best in cold, well-oxygenated water.

Living without oxygen. When the water runs out of oxygen, the painted turtle switches to anaerobic metabolism, which does not need oxygen. This produces lactic acid, which would normally be fatal. Painted turtles survive it because their shell and skeleton release calcium and magnesium carbonates that neutralize the acid, and the shell also stores part of the lactic acid. In laboratory studies at about 3 °C (37 °F), western painted turtles have survived around 170 days without any oxygen, one of the longest periods known for any air-breathing vertebrate.

Not all turtles are this tolerant. Map turtles and softshell turtles depend more on oxygen in the water, so they choose different overwintering sites from painted turtles.

How do box turtles survive the winter?

Land turtles cannot hide in a pond, so they go underground. In autumn the eastern box turtle digs into loose soil, leaf litter, rotting stumps, mammal burrows or the mud of a stream bank. Turtles in the north may burrow as deep as about 60 cm (2 ft), close to or below the depth where the soil freezes, and some return to the same site year after year.

Box turtles stay in their shelter until spring, usually emerging in April. During warm spells they sometimes wake, move and dig in again elsewhere. Laboratory studies have found that adult box turtles can survive brief partial freezing of their body fluids, but a turtle that freezes deeply or for too long dies, which is why choosing a well-insulated spot matters.

Tortoises in Europe and North America do the same. Hermann’s tortoises in the Mediterranean region dig into the ground for the winter, and desert tortoises in the American Southwest spend the cold months in burrows.

Baby turtles that freeze

Some hatchling turtles face winter in the nest. In the northern part of its range, the painted turtle often hatches in late summer but stays inside the shallow nest until the following spring. The hatchlings can survive in two ways: by supercooling, which means staying unfrozen below 0 °C (32 °F), and by tolerating the freezing of part of the water in their bodies for several days. Natural antifreeze-like substances and high levels of glucose help protect their cells. When the nest thaws in spring, the hatchlings revive and dig their way out.

Turtles that do not brumate

Not every turtle sleeps through the winter:

Sea turtles that fail to leave cold water in time can become cold-stunned when water drops below about 10 °C (50 °F). They float helplessly and wash ashore, and each autumn rescuers collect hundreds on beaches such as Cape Cod in Massachusetts.

Myths about turtles in winter

Myth: turtles freeze solid in ponds. No. Turtles at the bottom of a pond lie in water that stays above freezing. Only hatchlings in shallow land nests regularly survive partial freezing.

Myth: a turtle seen under the ice is dying. Not necessarily. Snapping and painted turtles can be active at very low temperatures, and movement under ice is normal for them.