When mating season arrives, these frogs melt
During winters in North America, many amphibians dive or burrow deep to avoid freezing–but not the wood frog. These fig-sized croakers remain aboveground as the water between the cells freezes. They spend the entire season in a type of cryosleep.
When spring arrives, most wood frogs awaken from their icy slumber with one thing on their mind: sex. Ryan Calsbeek from Dartmouth College, a biology professor who studies amphibians’ sex lives, says that males will find a temporary vernal pool or pond and call to females using sounds “almost as a quacking duck”. The forest can hear the cacophony from males as more join in.
Hearing the come-ons from the ponds around them, females hop toward the croaks they find most seductive. Calsbeek discovered that wood frogs’ female counterparts can’t resist the sound of deep, husky voices in a recent study. These croaks are more common in large frogs. However, once a female is lured into a pond, all male frogs will be able to hear them, even small sopranos. The male who grabs and mounts the female and wraps his forelimbs around her body, known as amplexus, is the victor. He squeezes until the female deposits her eggs in the water. Then he releases sperm and fertilizes the eggs.
It’s female wood frogs’ fate to have several breeding opportunities during their two-to-three-year life span. There are good chances that they will find at least one large baritone daddy.
Lithobates sylvaticus are the only amphibians found north of the Arctic Circle. They can be found in tundra, grassland and forest habitats in Canada and the United States.
Wood frogs’ bodies produce a sort of natural antifreeze that prevents their cells from bursting as they ice over during the winter. To help females, males’ thumbs expand during breeding.
This story appears in the October 2022 issue of National Geographic magazine.
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