Preparing for winter, amphibian style
BY THE MASKED BIOLOGIST
Special to the Star Journal
Perhaps it comes as no surprise that my children have at least a marginal interest in the outdoors. None of them plan to become biologists, that I know of, but they all love to learn about nature and spend time immersed in it. My youngest son watches a particular cartoon, Nature Cat, on PBS every morning before getting on the bus. This cartoon is well written and educational, as are most public television shows. It tries to address what has become known in my circles as Nature Deficit Disorder, encouraging children to play in the dirt—almost unheard of in modern times! It also focuses on nature, and not just nature on other continents as some do; it does a great job of focusing on habitats and wildlife children would encounter right here.
In a recent episode, a mouse and toad had a scheduled playdate, but the toad was feeling sleepy and wanted to get ready to hibernate; Nature Cat and crew helped her find just the right spot to hibernate, what we call a hibernaculum. This got me thinking, even though I know the different way amphibians hibernate, it would be a timely topic now that we are finally getting more seasonal weather. I have a fascination with amphibians, and their life cycle, and how they survive the winter is truly noteworthy. The American toad, very common in our area, digs in to wait out the winter. They are excellent diggers, and tunnel down to a depth where the ground will not freeze. This is no small task in the Northwoods, where frost depths can reach 70-80 inches—over six feet! There will be no food or water in the hibernaculum, the toad will just have to sleep through the long cold winter and return to the surface in spring.
Some of our frogs hibernate by dropping to the bottom of a lake, stream, river or pond that does not freeze to the bottom. Leopard frogs and tree frogs are a great example. They sit on top of the mud, relying on the dissolved oxygen in the water to move through their skin and keep them from drowning. They are very inactive during this time, not really having any food to keep energy up. They are cold-blooded, so their body temperature will lower to match that of the water. This causes their metabolism to drop and enter a sort of hibernation state. They may do some swimming around, moving when necessary, but will do so very slowly.
Frogs like spring peepers and wood frogs have a very special adaptation for winter weather. They allow themselves to freeze, after a fashion. The outsides of their bodies can actually freeze solid because they have a special kind of construction that keeps water in the cells at just the right amount that they do not shrivel and die or swell and burst at freezing temperatures. They also have a chemical in their system that acts as a kind of antifreeze to keep their internal organs from becoming damaged. This chemical is present in trace amounts all year, but as temperatures dip near or into freezing in fall, their bodies start to ramp up production and storage of this antifreeze to allow them to find a safe spot, settle in and go into an almost cryogenic hibernation state until the environment around them thaws in spring. No wonder these frog species are the first to start singing to welcome spring!
The Masked Biologist earned a bachelor of science degree from a university with a highly regarded wildlife biology program. He has work for natural resource agencies from the Rocky Mountains, across the Great Plains and into the Midwest, which provided opportunities to work with a variety of common and rare fish, plant and wildlife species. Follow The Masked Biologist on Facebook.