During winters in North America, many amphibians dive or burrow deep to avoid freezing—but not the wood frog. These fig-size croakers stay put aboveground as the water between their cells freezes, and they spend the season in a kind of cryosleep.

When spring arrives, most wood frogs awaken from their icy slumber with one thing on their mind: sex. Males find a pond or temporary vernal pool and call to females with sounds “almost like a quacking duck,” says Dartmouth College’s Ryan Calsbeek, a biology professor who studies amphibians’ sex lives. As more males join in, the cacophony of croaks can be heard throughout the forest.

Hearing the come-ons from the ponds around them, females hop toward the