Autumn Calls of Spring Peepers

Many people associate the call of peepers, the smallest frog in Connecticut, with the arrival of spring. Recently, while hiking on a warm fall day, I heard the “peeping” of Spring Peepers (Pseudacris crucifer). It wasn’t the huge chorus you usually hear at vernal pools and shallow ponds in March and April. It was just a few individuals calling back and forth. Instead of at the water’s edge, the sounds were coming from under the leaf litter. Why call in the fall, when it is not the mating season? Are these a different species?

I also checked out a vernal pool where I know Wood Frogs (Rana sylvatica) call in spring. There was actually a small chorus of them “quacking” in the leaf litter near the water. What’s going on?

Spring Peepers, and sometimes Wood Frogs, can actually be heard calling in the fall. The Spring Peeper’s autumn calls sound a bit harsher and more abbreviated, with less of the sleigh bell-like chorus that you hear in the spring. Lang Elliot, a biologist who has recorded many sounds in nature, captured the calls of fall peepers.

Both Spring Peepers and Wood Frogs are getting ready to go into a very deep sleep called torpor. Their bodily functions slow down and they go into a near-death-like state—part of their bodies actually freeze! Although the spaces between their cells can freeze, they prevent their cells from freezing by producing glucose, thereby keeping vital organs alive.

There are several hypotheses as to why these frogs are calling in autumn, but one has to do with environmental conditions. The shortness of the days, lower angle of the sun, increasing rainfall, and cooler temperatures are very similar to spring conditions when these frogs become active. Some may be responding to these environmental cues.

I asked frog biologist David Skelly, director of the Yale Peabody Museum of Natural History and Frank R. Oastler Professor of Ecology at Yale, about it. He said in autumn, the weather can be like the spring breeding period. “These environmental cues may prod them into calling, since they undergo physiological changes during late summer and fall that will enable them to breed as soon as they become active after a long period of dormancy.”

The name Spring Peeper is not a misnomer. Peepers are a sure sign of spring. But you may also hear them and their Wood Frog cousins in the autumn months as these tiny creatures get ready to launch themselves into the mating game.