Freezing temperatures are for the birds; at least they can migrate south if they feel like it. Other critters that can’t spread their wings aren’t as fortunate and have to hunker down and tough out winter’s chill. During most winters you may not even think about these animals because they are often out of sight and out of mind.
Shelter From the Storm
However, just as waterfowl have found ways to exploit habitats to survive, less mobile creatures have found strategies that get them through most years in their home range. You and I can throw another log on the fire or put on a couple extra layers of socks. Mammals such as deer, raccoons, and coyotes can grow a winter coat. Frogs, turtles, and snakes, on the other hand, have to seek out locations with better insulation, because they don’t have any of their own. While we may not think of these sites as warm and toasty, by wedging under logs and leaf litter, burrowing in the mud, hiding down in a crayfish burrow, or residing in deeper water can provide enough shelter from the air temperatures to stay above freezing.
Even when air temperatures dip into the teens at night, it takes a consistent hard cold spell to drop soil temperatures below the 32 F mark. For example, last month we had a couple days where the highs were in the 20’s and 30’s but the nightly lows were hovering around 10 degrees. During this time the soil temperatures only two inches down stayed above freezing. Shallow water habitats were frozen over with a couple inches of ice, but any deeper than that and it was balmy enough for bugs and fish to be swimming around.
In contrast, during the past couple of days the warmest temperatures haven’t topped 10 degrees in southeast Missouri. Likewise the duration and depth of freezing conditions has extended its grip further than we saw last month. Reports for the 2 inch soil temperature during this time have diminished to a frigid 31 degrees. While freezing temperatures may be tolerated for a short span (6 hours) by some amphibians, longer extents (> 24 hours) are tougher for some species to come back from.
With temperatures extremes like these another strategy is required to survive until warmer seasons. Similar to the old adage, “if you can’t beat them, join them”, some amphibians have developed a way to embrace the freezing temperatures. Nearly a quarter of Missouri’s frogs have this added adaptation. Wood frogs, eastern gray tree frogs, spring peepers and western chorus frogs all have a degree of freeze tolerance. These species have been found to tolerate temperatures ranging between 24-28 F up to two weeks. This is because as temperatures near that magic mark their livers begin to secrete sugary compounds in the form of glucose or glycerin, depending upon the species. This sugary mixture saturates body fluids and organs, acts like a form of antifreeze, and helps protect tissues from the cell damage that could occur as the creatures become living popsicles. During this cryogenic process the metabolism slows down along with the heart rate until everything stops, only starting again once conditions thaw back out.
Nature dishes out a myriad of challenges each season. Freezing temperatures in winter is just one obstacle that species have found multiple solutions to overcome. Some hightail it to warmer climes. Others find a cozy insulated spot. If that isn’t enough, others can just grin and bear it, all be it, it is a frozen grin, till warmer days roll around.
I don't know about you, but I'm glad I'm not a frog and can put another log on the fire. Stay warm this winter, whichever strategy fits you best.