Hibernation in Frogs and Toads

During the summer, frogs and toads can be found in ponds, streams, and ditches. They are very active and conspicuous during these warm months but are absent during the winter. Where do frogs go in the winter? They hibernate!

Amphibians, including frogs, are cold-blooded creatures. The technical name for this is ectothermic, which simply means that their body temperature is influenced by environmental temperatures. So, when the temperatures are cold the frogs get cold too and they must hibernate.

Frogs that are highly aquatic, like bullfrogs and green frogs, will hibernate directly in the water. Contrary to popular belief, frogs do not burrow into the mud during hibernation. Generally the frogs will lay on the bottom of the pond during the winter. Gasses are exchanged through the frogs' skin while they are inactive during hibernation, and they will live off body stores of fat to get them through the winter (much like hibernating mammals).

Frogs may not be entirely inactive during this time of hibernation, but may swim around from time to time. In fact, they can serve as a main source of food for fish like pike during the winter months.

Hibernation in amphibians that are more terrestrial, such as toads, simply burrow down into the ground to hibernate. These species must burrow down deep enough to get below the frost line, the depth of which varies with latitude. Terrestrial frog species that cannot burrow find pre-existing burrows and crevices.

Hibernation is most interesting in a species known as the wood frog. This species is found in northern climates, including Canada and Alaska. These frogs simply burrow underneath leaf litter on the forest floor and freeze solid. The physiology of the wood frog has evolved to produce an anti-freeze of sorts. Water is pulled out of the cells and replaced with this anti-freeze. So, when the frog tissue freezes, ice crystals do not damage sensitive organs. When springtime comes the wood frogs warm up, thaw out and go about the business of laying eggs and eating insects.

Sadly, many frogs do not make it through the process of hibernation. Many times oxygen in the water can be depleted to levels that are lethal from excessive ice and snow cover. If a body of water freezes solid, frogs found on the pond's bottom will retreat into the mud, which does not contain enough oxygen to sustain them. So, it is likely that in years with harsh winters the songs of springtime frogs may be a little quieter than normal.