Spring Peepers was originally published in the BFEC Newsletter Vol. 15/No. 2, Spring 2011.
Even as ice stubbornly clings to pond edges in late winter, optimists waiting for spring bend their ears hoping to hear frogs.
Incredulous but delighted, at the BFEC we sometimes hear spring peepers in late February. As the weather warms, these otherwise tiny, reclusive frogs gather by the hundreds to sing an undeniable pronouncement of spring.
True to their name, their call is a high-pitched "peep," created by males as they push air out of throat sacs. The faster and louder a male sings, the more likely he is to attract a mate.
Depending on the size of the congregation, spring peepers can be heard up to two miles away. Amazingly, the cacophony emanates from a frog that is "small enough to sit on a dime."1
Spring peepers are rarely seen. Even while loudly declaring themselves in the spring, it takes hard work to find one, often requiring a wet, night-time adventure with a flashlight and patience. Their tan color, with a darker x-shaped marking across the back, is perfect camouflage.
Some of our most familiar frogs, such as bullfrogs, have a habit of visibly basking along pond edges most of the year, and have helped create the misconception that other frog species do the same.
This is not true for many smaller frogs such as spring peepers, which return to water only in the spring to breed. Though they may not travel more than 1,000 feet from breeding sites, they spend the rest of the year in marshy woodlands hiding under fallen leaves and logs.
As a kind of tree frog, spring peepers have large toe pads for climbing, but they usually remain on the ground or in low vegetation. They emerge at night to hunt spiders, beetles, and flies, though they are not picky; whichever small insects cross their paths are likely dinner.
Spring peepers hibernate in shallow burrows among the fallen leaves of the forest floor. While this cover does provide some protection, it does not exactly insulate them from freezing temperatures. How do they manage?
Incredibly, they can create their own antifreeze, as can four other North American frogs species (including the wood frog and grey tree frog).
Their antifreeze takes the form of glucose, which they can concentrate in body fluids from 10-100 times above normal levels.2 (For the folks out there who love big words, the process is called “hepatic glycogenolysis”).
Sugars are pumped into cells and organs, preventing water molecules from binding to each other to form destructive ice crystals. Spaces outside of cells and organs, or up to 50% of the frogs’ body, do freeze, however, and can remain this way for up to three days.3
Spring peepers remaining frozen for longer periods are less likely to survive, and almost none do after remaining frozen for a month.
While in this semi-frozen state, their metabolism essentially shuts down, with no heartbeat, breathing or blood flow. Within a day, however, they thaw out and resume normal activity.
Once peepers thaw out, it’s time to navigate to water! But not just any body of water will do. They prefer ponds with no fish or very shallow edges, since spring peepers (and their progeny) make easy prey. Brush or shrubs at the waters edge are highly sought after sites, where males establish territories.
In addition to ponds, spring peepers and many other amphibians make use of vernal, or seasonal, wetlands for breeding. These wetlands contain standing water only during wet spring months, and lack many of the predators found in larger bodies of water.
Vernal wetlands do, however, present the challenge of drying up quickly in drier seasons. Spring peeper tadpoles usually take 90 or so days to mature into adults, but have been reported to do so as quickly as 55 days in dry conditions.
The feats of the spring peeper seem especially amazing when thinking of them in human terms. Humans hardly have the ability to speed up gestation to five months instead of nine, or withstand a 100-fold increase in blood sugar. (Diabetics know that we would perish long before then.)
There is one similarity: anyone who has been to a night club knows that a hundred men in one spot trying to attract women is indeed noisy, though we hope that the songs of spring peepers are slightly more charming.
Hear them yourselves this spring at the BFEC ponds, located next to the farm house or along our wetlands run trail.
1. www.dnr.state.oh.us/home/species_a_to_z/speciesguideindex
2. Storey JM; Storey KB. 1985. Adaptations of metabolism for freeze tolerance in the gray tree frog, Hyla versicolor. Can J. Zool. 63: 49-54.
3. Ahukwe, KPN. 2001. The Hidden Powers of Animals: Uncovering the Secrets of Nature. London: Marshall Editions Ltd. 240.