Have you ever wondered where frogs go during the winter? Well the simple answer is, they hibernate! Many believe frogs and toads bury themselves in mud and camp out for the winter, but it’s a bit more complex than that.
Species that hibernate during the winter start by making a “hibernaculum” or a living space. You may already know of many species that hibernate in Ontario including; bears, groundhogs and bats! Amphibian species also use hibernation to help them survive the harsh conditions of winter, but they do it a bit differently than other species. There are two main strategies used by frogs to survive the winter. Some species of frogs hibernate submerged in the deep waters of lakes, ponds and rivers, but there are also some species that remain on land and allow their bodies to freeze!
How is it possible for frogs to stay below water for months on end without drowning or freezing? This is a fascinating question. Frogs have lungs and breathe similarly to humans, but they also have specialized skin that can directly absorb oxygen from the water surrounding them. During the winter, frogs retreat to the deeper waters of lakes, ponds and rivers and float on the bottom. As long as the water does not freeze, neither will the frogs! Another interesting fact is frogs do not bury themselves in the mud, as some turtles do. Turtles are able to slow their metabolism more than frogs and can survive off the limited oxygen available in mud. Frogs on the other hand, need much more oxygen to survive which is provided by floating in the water. Gases can be exchanged much more rapidly between the air and cold liquids, meaning that cold water can hold more oxygen. As long as the water does not completely freeze over, bodies of water in the winter are pretty oxygen rich.
During long, cold winters "winter kills" can occur. If ice covers the entire body of water, it can limit the amount of oxygen entering the water. This usually occurs to smaller bodies of water, rather than large lakes or rivers. Once ice covers the entire surface, gas cannot be exchanged and oftentimes the oxygen supply depletes rapidly. This is a natural occurrence that can impact the survival of species hibernating beneath the surface.
Some species of frogs do not submerge themselves in water to hibernate. There are actually some species that are freeze-tolerant! Wood frogs and 3 species of tree frogs in Ontario are considered ‘freeze-tolerant’. These species hibernate on land, by buying themselves in leaves and dirt. Once temperatures reach about -5 degrees celsius, ice crystals form in their bodies freezing up to 40% of the water in their bodies. The internal systems in these frogs essentially “shut off” for the winter, blood is no longer pumped and they don’t have a heartbeat. Before temperatures reach below freezing, their bodies produce urea and glycogen which act as ‘cryoprotectants’ which helps limit the amount of ice forming in their bodies and protect their cells against shrinking. No other animal can survive freezing, but once the temperatures warm up these frog species thaw and hop away!
Photo from Royal Ontario Museum
The Frontenac Arch Biosphere has many species of frogs; including the Wood frog, the Spring peeper and the Green Frog. The Wood Frog and Spring peepers are considered ‘freeze-tolerant’ and use the strategy of allowing their body to freeze to survive the winter. The Green Frog uses the first hibernation strategy and spends the winter submerged in water.
The Frontenac Arch Biosphere contains over 200 named lakes, 2 major rivers and many wetlands, which provide critical habitats for the frog species that are found here! Recently the significance of the Thousand Islands ecosystem, including the Thousand Islands National Park was recognized by the Canadian Herpetological Society as an important reptile and amphibian habitat area (IMPARA)! These ecosystems support the critical habitat for many native reptile and amphibian species, including the frog species mentioned above. Recognizing the importance of the areas for reptile and amphibian habitat supports conservation initiatives and research!
Click here for more resources on IMPARAs!