Critter of the Month: Spring Peeper
The spring peeper is a small tree frog known for its chirp-like call heard on warm spring and early summer nights. Hundreds of adult frogs will gather in swamps and marshes and call in chick-like fashion as part of their mating ritual. The calls can be heard as far as 2 1/2 miles away, depending upon the numbers, and for many Wisconsin residents, this sound marks the beginning of spring.
Where do they live?
There are two species of spring peepers. The southern spring peeper is found along the coast of the Gulf of Mexico, but it is the northern species that is native to Wisconsin. The northern spring peeper is found throughout the Eastern United States and Eastern Canada and is considered very common.
Spring peepers prefer damp forests and wetlands. Though very capable climbers, these frogs are more comfortable on the forest floor, hiding in the vegetation and leaf litter.
What do they look like?
Spring peepers are very small frogs with adults only growing to approximately an inch long, about the size of a paperclip. They are generally tan or brown, though some color variations of gray or olive green are possible. These frogs usually can be identified by a dark cross or “X” on their backs. Females are lighter in color.
Males tend to be smaller in size than females. Males also have dark throats which contain a large vocal sac. When they call, the vocal sac expands like a balloon to about the diameter of a quarter. To make the sound, they close their nostrils and mouths and squeeze the air out of their lungs. The sound is created when the air flows across their vocal cords and into their vocal sacs. Only the males make this sound.
How do they live?
These small frogs are insectivores, eating ants, flies, spiders, and beetles. They are nocturnal, so they hunt at night.
Spring peepers are very tolerant of Wisconsin’s varying spring temperatures and can withstand partial freezing of their bodily fluids. When the temperature gets very cold, the frogs hibernate under logs and leaves. Spring peepers can survive with body temperatures as low as 17 degrees Fahrenheit.
What is their life cycle?
In the spring, large groups of spring peepers gather along the edges of swamps, marshes, bogs, and ponds and begin their mating ritual, as males call loudly to attract females. In Wisconsin, spring peepers generally breed from April through June.
Females attach their eggs to vegetation under the water line in clusters of two or three and can lay as many as 1,000 eggs per season. Eggs will hatch into tadpoles anywhere from two days to two weeks later. Tadpoles eat algae as they grow and transform into frogs in two to three months’ time. Within a year, these new frogs will fully mature into adults. If not eaten by their many predators (snakes, salamanders and birds of prey), Spring Peepers can live three to four years.
What are their threats?
While spring peepers are very common and considered stable in most areas, their habitat is changing due to loss of wetlands in many states. They are listed as threatened species in Iowa and Kansas.