Amphibians
Spring Peeper
Pseudacris crucifer · also called spring peeper, northern spring peeper
The spring peeper is a frog most people hear thousands of times and never see. It is smaller than a coin, hidden in leaf litter and pondside brush, and its shrill, sleigh-bell chorus on the first warm wet nights of the year is, across much of eastern North America, simply the sound that means winter is over.
Overview
Spring peepers live in wooded and brushy country near water — ponds, ditches, marshes, and wet meadows — throughout the eastern United States and southeastern Canada. Outside the breeding season they are terrestrial, foraging on the ground and in low vegetation for small insects and spiders, and they are nocturnal and very hard to spot. Their name comes from the male’s call and from their timing.
The chorus
In late winter and early spring, males gather at breeding pools and call from stems and grass at the water’s edge: a clear, high “peep” rising at the end, about once a second. Each male has a throat sac nearly its own size that works as a resonator, and a large chorus can hit 90 decibels and carry for over a kilometre. Males space and time their calls in relation to their neighbours, forming shifting duets and trios, and a calling male damps its own hearing to protect its ears from its own volume.
Frozen and revived
The peeper breeds so early because it can function in the cold, and it survives the cold itself through freeze tolerance. In hard frost, its liver releases a surge of glucose that protects its cells while up to about 65% of its body water turns to ice. Its heartbeat and breathing stop. On thawing, it restarts and is soon active — a routine part of its year.
Life cycle
After mating, females attach several hundred eggs singly or in small clusters to submerged plants. Tadpoles develop over roughly two to three months and transform into froglets a few millimetres long, which disperse into the surrounding woods.
Status
The spring peeper is Least Concern, abundant and adaptable. Local populations depend on the survival of small breeding wetlands and the woodland around them, which are vulnerable to drainage and development, and — like all amphibians — the species can be hit by disease and pollution, but overall it remains one of the most common frogs in its range.
Spring Peeper: common questions
What makes the spring peeper's call so loud?
A male peeper inflates a balloon-like vocal sac under its chin, nearly as big as the frog itself, and uses it as a resonator, forcing air back and forth over the vocal cords. Relative to its tiny body the output is enormous — around 90 decibels at close range, comparable to a lawnmower — and a chorus of hundreds or thousands of males at a breeding pond is loud enough to be uncomfortable to stand beside and to be heard more than a kilometre away. Calling is energetically brutal; a peeper's calling muscles are among the hardest-working of any vertebrate.
Why is it one of the first frogs to call in spring?
Spring peepers breed very early, often while there is still ice at the pond edges and snow in the woods, because they can operate at low temperatures that keep competitors and many predators inactive. Males emerge on the first mild, wet nights of late winter and start calling from vegetation at the water's edge; in the southern part of the range this can be January, and further north it is March or April. The sudden arrival of the chorus is, for many people, the definitive signal that winter is breaking.
How does a frog survive being frozen?
The spring peeper is one of a handful of frogs with true freeze tolerance. As ice begins to form in its body, its liver pumps out a flood of glucose that saturates its cells and acts as an antifreeze, protecting them from the damage that ice crystals would otherwise do. Water in the spaces between cells freezes — up to about two-thirds of the frog's total body water turns to ice — its heart and breathing stop, and it is, functionally, a frog-shaped block of ice. When temperatures rise it thaws from the inside out, the heart restarts, and within hours it is active again.
What is the X on its back?
The spring peeper's most reliable field mark is a dark, roughly X-shaped or cross-shaped marking on its otherwise tan, brown, or grey back — the species name crucifer means "cross-bearer." The exact shape varies between individuals and the ground colour can change somewhat with temperature and background, but the X, along with the small size and the toe pads, distinguishes it from other small frogs in its range.