Boreal chorus frog

A finger-sized frog whose spring trill fills Rocky Mountain wetlands, and whose cells can freeze solid and still wake up.

  • A boreal chorus frog at Seedskadee National Wildlife Refuge, Wyoming.USFWS Mountain-Prairie
  • A boreal chorus frog showing the dark back stripes used to identify the species.Peter Paplanus

Boreal chorus frog at a glance

Pseudacris maculata BOR-ee-uhl KOR-uhss FROG; Pseudacris maculata is soo-DAK-riss mak-yoo-LAH-tuh

Type
Amphibian · frogs
Diet
Insectivore
Size
About 1 inch long, small enough to sit on a fingertip (adults run 0.7 to 1.5 inches).
Lifespan
Most chorus frogs live only a year, and rarely more than two or three, in the wild.
Conservation
Least concern

Eats small insects, spiders, other invertebrates

It hunts by sight from the ground or low plants near water, snapping up small invertebrates it can overpower.

Should you worry?

Completely harmless. It's tiny and shy, so the real trick is finding one — look near where you hear the trilling instead of expecting to spot it easily. Wash hands after any handling and leave egg clumps in the water.

Spring at a Rocky Mountain wetland starts with a sound, not a sight: a rising trill, like a fingernail dragged down the teeth of a comb, coming from everywhere in the grass at once. Dozens of boreal chorus frogs can be calling within a few yards of a trail, and almost nobody sees one. They’re barely an inch long, the color of dead grass, and they call from inside the thickest cover they can find. The chorus is the frog. Chasing the sound rather than expecting to spot a body is the only way this works.

A few weeks before that chorus starts, most of those same frogs were frozen. Boreal chorus frogs spend the coldest months tucked into leaf litter or under fallen wood, and when the temperature drops far enough, the water in parts of their bodies actually turns to ice. Instead of dying, the frog’s body floods itself with glucose, a natural sugar that keeps ice crystals from tearing apart its cells. Its heart stops. Its breathing stops. Then the ground warms, the ice inside it melts, and the same frog that was solid a month earlier climbs out and starts trilling for a mate.

That trick is why the sound shows up so reliably, year after year, even after a hard winter. A pond that looked lifeless in March is loud with chorus frogs by May, laying up to 1,500 eggs apiece in small clumps stuck to underwater stems. By early summer the trilling has mostly stopped, the tadpoles have grown legs, and the wetland goes quiet again until the next thaw brings the whole chorus back.

Did you know?

  • A boreal chorus frog can freeze solid enough in winter that its heart stops, then thaw out in spring and start calling again as if nothing happened.
  • Its call sounds like a fingernail dragged down the teeth of a comb, and a single wetland can hold dozens of males calling back and forth.
  • A female can lay up to about 1,500 eggs, glued in small clumps to underwater plants instead of one giant mass.

Common questions

Are boreal chorus frogs poisonous? Can I touch one?

No. They aren't poisonous, and holding one gently and briefly is safe — just wash your hands afterward and put it back where you found it.

What does a boreal chorus frog sound like?

A rising trill, like running a fingernail down the teeth of a comb. It's one of the first frog sounds of spring.

How does a chorus frog survive freezing winters?

Its body fills with a natural sugar called glucose that works like antifreeze, so ice crystals don't destroy its cells while it's frozen.

Where do boreal chorus frogs live?

In shallow wetlands, ponds, and wet meadows — anywhere with quiet water for laying eggs in spring.

Why is it so hard to actually see one?

It's tiny, well camouflaged, and usually calls from inside thick grass at the water's edge, so most people hear dozens without seeing a single frog.

Where it lives

Where we got this