The American Bullfrog, a common frog species found throughout Michigan
Winter is slowly creeping across Michigan and inevitably ice will cover most bodies of water, creating a winter wonderland without reptiles and amphibians. But where do they all go? Do they hibernate? Freeze? Relax? Well, surprisingly, it is a little bit of everything for Michigan’s common cold-blooded animals.
Amphibians and reptiles are cold-blooded, meaning they cannot produce internal body heat. During warmer months it is not uncommon to see painted and snapping turtles basking on a floating log in the Red Cedar or a snake spread out on top of a warm rock. During the winter however, they each seek shelters and have evolved many different ways to deal with the frigid Michigan winters. Many cold-blooded animals burrow deep into the soil or mud and then go dormant so they do not freeze. By slowing down their body functions they save energy and do not need to eat all winter long.
Unlike humans which require a consistent body temperature, cold blooded animals take on the temperature of their surroundings. When the environment is warm they are warm and when it is cold they are cold. Cold-blooded animals tend to be much more active in warm environments because their muscle activity depends on chemical reactions which run quickly when it is warm and very slow when it is cold.
In the winter as water begins to freeze most aquatic turtles find a nice spot in the mud at the bottom of a lake or pond close to shore and under the ice. Their metabolisms dramatically drop and they will not come out of the water for air until springtime. Even though they do not breathe they still require some oxygen. They do this by taking up dissolved oxygen from the water through their skin. They get energy from their body tissues and the calcium found in their shells neutralizes lactic acid build-up, allowing them to survive with limited oxygen. Sometimes if you look really hard you may even see one moving around under the ice!
Aquatic frogs, including the leopard frog and American bull frog, typically hibernate underwater. A very common misconception is they spend the winter the same way that aquatic turtles do, dug into the mud. However, frogs would suffocate if they dug into the mud for long periods of time. Instead hibernating aquatic frogs must have a higher level of oxygen in the water and spend the majority of their time lying on top of the mud, they even slowly swim sometimes.
Terrestrial frogs are a little different, they tend to be diggers and like to burrow deep into the soil below the frost line. Some frogs such as the wood frog and the spring peeper are not adapted to dig and instead find deep cracks and crevices in rocks, logs, and leaf litter to protect themselves from the frigid temperatures. Some frogs can even freeze, such as the North American wood frog and yet still live. They have a natural anti-freeze in their bloodstream that prevents ice crystals from forming in vital organs. A partially frozen frog for will stop breathing and will not have a heart beat however once spring approaches the frogs body will thaw and inevitably it will come back to life!
Snakes are very similar to turtles and frogs in that they seek shelter during the cold winter months. Their thin scales do not provide much insulation to their fragile bodies. Typically snakes spend the winter in a dormant state in underground rodent burrows or other natural frost free shelters. Sometimes they even seek out basements and houses with cracked foundations.
In many ways winter is a quiet season, however Michigan’s lakes, streams, and ponds are nothing short of a sleeping vibrant ecosystem. A wonderland in and of itself.