How Do Frogs Survive the Winter (When It Feels Like We Humans Hardly Can)?

Wind chill, polar vortex… brrrr… it’s been a frigid few months. Regions throughout Canada have experienced one of the coldest winters in decades.

Most of us are fortunate to have warm shelter and proper winter clothing to protect us from the elements. But how do animals survive harsh temperatures?

At the Canadian Museum of Nature, we have a live-animal exhibition currently on view called Frogs – A Chorus of Colours. I spoke with Elisa Caballero—a frog-keeper from Clyde Peeling’s Reptiland, the zoo that produced the show—to learn how frogs cope with extreme seasons and conditions.

Two American bullfrogs.

American bullfrogs (Lithobates catesbeianus).

Frogs are very interesting creatures in many ways, especially in their adaptations. Different species have special tactics for surviving the deep freeze. Aquatic frogs, such as the American bullfrog (Lithobates catesbeianus, which you can see in this exhibition), hibernate in water during the winter. They descend to oxygen-rich water and their metabolism slows down. The northern leopard frog (Lithobates pipiens—we have some temporarily residing in our RBC Blue Water Gallery) also hibernates this way.

The American toad (Anaxyrus americanus americanus) has thick, dry skin and can burrow deep-enough below the frost line for the winter, where it hibernates.

Three northern leopard frogs in a terrarium.

Northern leopard frogs (Lithobates pipiens).

Other species such as the wood frog (Lithobates sylvaticus) and the spring peeper (Pseudacris crucifer) must rely upon their “antifreeze” capabilities. They actually freeze—ice crystals form in fluid compartments such as the bladder. As long as not more than 65% of the frog freezes, it can survive. It does so by manufacturing high concentrations of glucose (sugar) or sugar alcohols in its cells. The thick, syrup-like solution props up the cells so they don’t get damaged. Their heart and lungs stop functioning, but resume their action when the frog thaws upon the return of warm temperatures. These frogs hibernate in places such as leaf litter or in cracks in logs.

Most of the species in Frogs – A Chorus of Colours are tropical, so they don’t have to worry about freezing during part of the year. But hot conditions in the desert or on the savannah can also pose problems. The African bullfrog (Pyxicephalus adspersus; be sure to check him out in the exhibition—he’s a big guy!) relies on a cool process called estivation.

An African bullfrog in a terrarium.

African bullfrog (Pyxicephalus adspersus).

Basically, estivation involves burrowing a few feet into the ground and remaining there during the excessive heat or drought. The frog’s breathing and metabolism slow down and its body temperature drops. Conserving energy this way means that the frog can go prolonged periods of time without food (similar to hibernation). He also grows a few extra layers of mucusy skin before estivating to prevent water loss.

Visit Frogs – A Chorus of Colours (on until May 11) to learn more about the different frog species and their cool adaptations. If you see Elisa working around the displays, taking care of the frogs and cleaning their habitats, be sure to say hello and tell her you were reading about frog hibernation and estivation.

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