Up and out early from the deepest of sleep

Up and out early from the deepest of sleep
John C. Lorson

The range of the wood frog extends all the way to the Arctic Circle — further than any other amphibian in North America — thanks to some amazing adaptations that allow the frog to survive temperatures far below freezing while it waits out the winter under leaf litter on the forest floor. I photographed this wood frog in mid-December on the Holmes County Trail.

                        

It’s early February, and “The Groundhog” has said his piece. Whether you’re inclined to follow the forecast of Pennsylvania’s legendary prognosticator, Punxsutawney Phil, or Ohio’s own fur-coated forecaster, Buckeye Chuck, the call this year is the same: Spring is “right around the corner.”

Even though I love the idea of large numbers of humans — many of whom wouldn’t know a groundhog from a prairie dog — embracing the idea of looking to nature for clues about the world around them, I don’t personally place much faith in the thoughts and actions of an oversized ground squirrel. I’ve been burned far too many times by predictions that have swung seriously awry. Personally I find the phrase “right around the corner” a bit too vague to hang any serious plans upon.

Whether or not we’re about to experience an early spring, as warm-blooded creatures the timing is of no great consequence. We can take today’s temperature of 55 F as a gift of comfort and live with tomorrow’s 20 F as a minor inconvenience. As homeotherms our bodies “automatically” maintain the same, steady, internal temperature and level of metabolic function. We can still think, feel and move about freely.

The situation is entirely different for our ectothermic or “cold-blooded” counterparts. A creature whose body temperature is determined by the temperature of its immediate surroundings becomes more sluggish as the thermometer goes down. Survival below 32 F, the freezing point of water, requires special adaptations. Some weather the cold by going to a spot that isn’t likely to sink below freezing — the bottom of a lake for example. Others deal with the cold in an entirely different manner. The wood frog is a fascinating example.

As the name implies, the wood frog is a resident of damp, temperate forests and woodlands of North America and ranges further north than any other amphibian on the continent, even crossing the Arctic Circle. The ping-pong-ball-sized frog sports a black mask across its eyes, and when involved in the business of breeding, it produces a sharp string of clucks that sound a lot more like a duck than a frog. Of particular interest to this discussion, however, is how the wood frog spends its winters.

Although wood frogs, as amphibians, are bound to water for reproduction, they spend most of their lives in the woods. When winter bears down, they find shelter in the forest duff, burying themselves under leaf litter. And while some amphibians and reptiles take great pains in selecting a spot deep enough underground to avoid freezing temperatures, the wood frog takes a decidedly different tack.

As winter approaches, the wood frog begins to stockpile its own urine in its bloodstream. As cold weather sets in, the frog’s liver begins to produce enormous quantities of glucose, which combines with the urea in the blood to form the frogs own brand of antifreeze! Water is driven from the frog’s major organs and cells to avoid the catastrophic effects of freezing, and the frog slowly cools to a state of suspended animation where all organs — including its heart — slow to a complete stop. Depending on the latitude, this state can last as long as eight months with the frog’s body temperature dipping as low as 3 F.

Among the earliest of amphibians to emerge in the spring — often while there is still ice present on the ponds and marshlands where they breed — wood frogs thaw with the rising temperatures, and their hearts resume right where they left off. After a few days of simply warming up and breathing, the wood frog eliminates the glucose and urea mix from its system and sets about the work of finding food, water and a suitable mate.

Thousands of adults often crowd into the same wetland areas and vernal pools to compete for a mate, and each successful female will lay up to 3,000 eggs in a gelatinous cluster. Shortly after the deed is done, all parties vanish back to the woods until the following spring.

Whether Buckeye Chuck is right or wrong, wood frog mating season will be upon us soon and should begin in earnest, alongside that of the tiny, enthusiastically vocal spring peeper near the end of February or beginning of March. Be sure to get out there and listen.

Write The Rail Trail Naturalist at P.O. Box 170, Fredericksburg, OH 44627, or email jlorson@alonovus.com with comments or questions about the natural world.


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