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Spring Peepers, Winter Sleepers

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Illustration by Adelaide Tyrol

In the realm of nature, mysteries often unfold beyond the limits of our perception. Not so with spring peepers. Stand at the edge of any wetland when peepers have reached full voice, and you will be engulfed in the world of another species. A piercing chorus of hundreds of males will wash over your sensory shores. The mating calls of the spring peeper are extraordinarily loud – nature’s choir fortissimo.

Peepers awake from their winter slumber, sometimes with snow still on the ground, ready to reproduce. During the previous autumn, the bodies of these tiny chorus frogs began their physiological preparations for the current mating season, a strategy that allows them to start the spring cycle as early as possible. Some males become so well prepared that they begin calling before winter arrives. In my nature journal, I have recorded hearing these “fall peepers” well into foliage season and beyond: one peeper began singing on December 7th, 1998, as the temperature reached the mid-50s.

When autumn wanes and temperatures drop below freezing, how does a one-inch frog survive the winter if all it does is snuggle beneath leaf litter or under a log or tree root? As a peeper’s temperature gradually drops, sugars begin to concentrate inside its cells and compose a kind of natural antifreeze. Individual cells expel much of their water so that ice, when it begins to form in small amounts, is confined to the spaces between cells, where its sharp edges won’t damage the cell contents of a peeper’s internal organs. Still, this strategy only works so well; a dormant peeper will freeze and die at temperatures below about 21°F (-6°C), so insulating snow cover (and a nice blanket of leaves and duff) is crucial.

Even though a spring peeper in winter is dormant and its body is cold, its cells and organs still need some energy to stay alive. But its body is receiving neither the oxygen nor the nutrients that would normally circulate in the blood of an active animal. To get around this, the peeper relies on energy stored the previous autumn. The same sugar that acts as antifreeze in the dormant peeper’s cells also serves as a source of nourishment, as do the glycogen reserves stored in its organs. These carbohydrates slowly ferment to provide a bit of energy for the sluggish metabolism of the dormant “peepsicle.”

As these carbohydrate supplies dwindle in early spring, peepers wake up and migrate to marshes, bushy swamps, woodland pools, and the edges of ponds. This is the easiest time to find the tiny, light-brown frogs. Look for the dark brown, X-shaped cross that marks their backs, which gives rise to the species name of “crucifer.” The 3/4-inch males are smaller than the females, which can grow to be 1¼ inches.

Males start to call as early as mid-March in southern Vermont and New Hampshire. They inflate a dark, olive-colored throat pouch to nearly the size of their body and use it to push air over their vocal cords, repeating this cycle and making a sound when they both inhale and exhale. Each piercing call rises in a crescendo. Listen closely to a peeper chorus, and you’ll soon realize that they play off each other, engaging in duets, trios, quartets, and more. Sometimes you can hear a bird-like trill, which males use to defend modest mating territories that range from about 4 to 16 inches across.

Peepers have an uncanny knack for positioning themselves so that the surrounding leaves and stems amplify their calls and cause them to seem as if they are emanating from somewhere else – a kind of natural ventriloquism. Combine this with an ability to change the tone of their skin color to match the environment, and it’s not surprising that it takes patience and, often, a strong flashlight to actually see a peeper calling.

When a female swims over to a singing male and touches him to indicate her amorous intent, he climbs onto her back and holds on tight as she swims around. Males fertilize up to 800 eggs as the eggs emerge from the female, with the eggs deposited individually or in small clusters on submerged vegetation. Females then retreat from the pond while their diminutive Don Juans continue to serenade for weeks, a few even crooning until the fireflies begin to sparkle.

Peeper populations are healthy throughout New Hampshire and Vermont. They thrive in wetlands and will reproduce as long as long as the water is not too acidic, requiring a pH above 4. Spring peepers aren’t experiencing the widespread growth deformities, such as missing limbs and digits, affecting some other local species of frogs. At the moment, the state of these boisterous and endearing little creatures is as bright as their familiar ringing calls.

Discussion *

Jun 07, 2014

Thank you.  On recent backpack hike, the group wondered what is the temp. range of when they will sing?  It seemed odd to me that on May 30th they were singing (1K ft in ADK).  I wondered if it was due to the cold spring, or was it still within an average breeding season?
Happy to have found your site.

tracy

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