On calm, mild evenings in autumn, a familiar sound may be heard coming from a stand of trees close to an alder thicket or a woodland swamp. A crisp, one-note “peep” infrequently breaks the silence in these wooded settings at night and during the day when the air is unseasonably warm and moist.
This distinct call can perplex anyone who has visited a wetland in spring. Can it possibly be a spring peeper, known for producing the seasonal chorus of natural music after the soil thaws in April? Following a summer of silence, the male spring peeper redevelops an urge to announce its presence, this time in the area in which it may have spent the past several months.
After occupying a brushy wetland for nearly two months in spring attempting to entice female peepers for mating purposes, the male abandons its breeding site and travels some distance inland. It is on rainy evenings or during heavy dews that this animal is most likely to leave the water and head toward a section of forest. Like all amphibians, the peeper must keep its skin moist in order to allow for the absorption of small amounts of oxygen. The distance a peeper travels after exiting the water depends greatly on the conditions of the surrounding forest and the outcome of encounters with rival peepers along the way.
In some cases, a peeper may have to venture over a half mile from its breeding wetland to find a suitable residence, while other individuals may need to go less than a hundred feet from their spring territory. Because of this nocturnal creature’s especially small size, and ability to blend in effectively with its background, researchers have experienced great difficulty in following the movements of the spring peeper after it leaves its breeding ground.
Throughout summer, the peeper feeds primarily on small invertebrates that it snags with its tongue. While not classified as a true tree frog, the peeper is known to climb into the lattice of twigs and branches of shrubs and saplings under the cover of darkness in its attempt to locate bugs.
Shortly after Labor Day, as the number of insects and other smaller forms of life dwindle, the body chemistry of the spring peeper begins to change. Along with forming a layer of fat, this amphibian, like the wood frog, gray tree frog and toad, starts to develop a high concentration of glucose in its blood and in various internal organs. As this substance accumulates throughout its body, water molecules are slowly displaced from each other, resulting in a lowering of the freezing point. As autumn progresses, the peeper becomes more cold tolerant and physiologically capable of withstanding temperatures that can drop into the lower 20s.
In the coming month, the peepers will retreat into sheltered spots on the forest floor to spend the winter. This small amphibian is often able to work its way under a fallen log, beneath a rotted stump or below a sizeable rock which helps insulate it from the cold. During periods of especially frigid weather, when the frost line descends to greater depths, the peeper may experience the formation of ice crystals within much of its body. This hardy amphibian is able to tolerate such normally lethal conditions and can recover when a thaw eventually occurs.
In spring, the peeper is quick to exit its winter residence on the forest floor and travel to a vernal pool in order to claim a choice spot for breeding. During this time, the peeper still retains a fairly high concentration of glucose in its blood in order to deal with those frequent occasions when a mass of cold air lowers the temperature to below the freezing level. As the threat of icy weather decreases during the spring, the level of glucose also drops, as a high concentration of this sugar in its body makes any creature more prone to infections.
Researchers are not sure why the peeper sings during the autumn. Certainly its call is far more sporadic at this time of year than during the spring when this cricket-size entity bellows out a note every second. The development of higher levels of glucose may provide them with the stimulation and energy to exercise their vocal cords, yet the purpose for this auditory display remains a mystery.
Photo: Spring Peeper, courtesy Wikimedia user Well Tea.
A version of this story first appeared on the Adirondack Almanack in October, 2012. Read more about reptiles and amphibians in the Adirondacks here.