As winter approaches, we know it’s time to start getting those warm clothes out of the closet. While we stay nice and toasty in our sweaters, many animals aren’t so lucky and have to find other ways to make it through the cold winter weather.
For example, many species of frogs survive the winter by entering a state of hibernation. Hibernation is a state of ‘dormancy’, like a long, deep sleep where the frogs’ activities slow way down for the winter. Frogs hibernate as an adaptation (a trait that helps them survive) to really cold temperatures. Some frogs in warmer climates also hideout, entering a state of dormancy to pass summer months that are hot and dry, a process called estivation.
For hibernating frogs, before they can wait out the winter, they need to find the perfect place to hibernate. These hibernation hideouts are called hibernacula (singular hibernaculum), and they can be on land or in the water
For land-loving terrestrial frogs like the Spring peeper and Striped chorus frog, a hibernaculum can be found under rocks, leaves, or in a log. The Wood frog also hides out on land, but after they bury themselves under debris on the forest floor, they turn themselves into frogsicles!
As the temperature drops, everything the Wood frog does stops. We mean EVERYTHING! It stops moving, breathing, its blood stops flowing and even its heart stops beating! During winter, 35-45% of the Wood frog’s body may freeze and become ice-like. It can pull this trick off by storing glucose in its liver. The glucose gets released into the frog’s blood while it’s ‘playing dead’, preventing its entire body from freezing. The glucose acts as antifreeze to keep this little guy alive while staying completely still. Once things warm up in the spring, the frog comes back to life (so to speak) and returns to its regular activities.
In the Water
Aquatic frogs spend the winter in the water at the bottom of a nice stream, river, lake, or wetland. The perfect hibernaculum spot often involves hiding under submerged vegetation or in some mud at the bottom of a body of water. Unlike aquatic turtles that dig deep into the mud to overwinter, aquatic frogs leave part of their skin exposed to the water so they can continue to breathe oxygen through their skin. Some aquatic frogs, such as the common Leopard frog in Ontario, may wake up from time to time and swim VERY slowly before going back to hibernating in their hibernaculum hideout. The Oregon spotted frog overwinters in still water that isn’t likely to freeze over completely and that is close to their breeding grounds.
For Oregon spotted frogs to move from the wetlands where they live during the spring and summer breeding season to their wintering area requires connected waterways so they can get around safely. Sadly, much of this wetland habitat is being lost to development, making it increasingly difficult for the Oregon spotted frog to survive, earning it the title of the most endangered amphibian in Canada. You can help protect the Oregon spotted frog by starting a Bring Back the Wild Campaign to fundraise in support of wetland rehabilitation and the breeding and release of this frog species back into the wild.