Monday, October 8, 2012

Adirondack Amphibians: Spring Peepers in Autumn

On calm, mild evenings in autumn, such as those that occurred last Wednesday and Thursday, 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 20’s.

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.

The weather forecast for the coming week or two is not indicating any hint of an “Indian summer”, however, once a spell of unseasonably mild temperatures occurs, it is possible to hear a sound normally associated with spring while on an evening stroll through a wooded area here in the Adirondacks.

Photo courtesy Well Tea.

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Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.

4 Responses

  1. Rich Merritt says:

    I’ve always heard this was due to the phenomenon of Autumnal Recrudescence. The theory is that when the length of days approaches a similar window to the active breeding season in the spring (the day length is the same) some creatures, perhaps confused, are thinking (albeit briefly) that it’s breeding time again. Some songbiirds will likewise warble their breeding songs for a few days in the fall as well. I’m wrong a lot but it makes sense to me.

  2. Paul says:

    Very interesting. There must be some kind of evolutionary advantage. You don’t let pdators know you are

  3. Paul says:

    oops sent too fast. …there without a good reason that you would want to pass onto the next generation. (that was predators). There is something about peeping in the fall that gives some frogs the reproductive upper hand.

  4. Tom Kalinowski says:

    Good the hear from you Rich: I, likewise, have read about Autumnal Recrudescence, but I have some problems with it concerning peepers. These amphibians begin peeping in the spring whenever the soil thaws, and not when there is a certain amount of sunlight. Their autumn peeping can be heard from Labor Day through mid October. Labor Day sunlight is equivalent to the light of the last days of Feb., not April. Like you, I am also wrong on a lot of things. I guess only the peepers know why they are peeping in fall.

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