On a recent hike on Fernalds Neck Preserve on Megunticook Lake, I heard a loud “peep” from amid the trees. My first thought was “Swainson’s Thrush.” While the song of this Maine breeding bird is a complex series of flute-like notes, its call note, which is what we’d be hearing now during the early weeks of fall migration, sounds a lot like that of a Spring Peeper. And I certainly wouldn’t be hearing a Spring Peeper on a humid morning in September.

The peeper’s fall quest results in it finding shelter for the winter under bark or fallen leaves and trees.

Or would I? As I listened more carefully, I realized it was in fact not a bird (or a plane) but an amphibian making that noise. The sleigh bell-like chorus of the Spring Peeper is one of our favorite harbingers of spring. But a Fall Peeper? What’s up with that? Turns out the somewhat misleadingly named Spring Peeper will peep well into fall, especially when the weather’s warm.

The tiny frogs won’t gather in a chorus as they do when they’re primed to mate. This time of year, the peeper disperses from the home range it established in spring to look for places to hibernate. According to Maine Amphibians and Reptiles (my bible for frogs, snakes, and turtles in this state), the Spring Peeper will travel up to 1000 yards from its home territory now. That doesn’t seem all that far to us, but for a frog that’s only an inch long, that distance must feel like a cross-country trek.

The peeper’s fall quest results in it finding shelter for the winter under bark or fallen leaves and trees. The seemingly delicate and thin-skinned little animal survives the cold of winter by building up glucose and an alcohol-based anti-freeze in its blood. These prevent the cells themselves from freezing, which would kill the frog. Like several other frog species, the peeper can withstand freezing solid for a surprising amount of time—and the blood chemistry of hibernating frogs has naturally intrigued scientists studying cryogenics. Perhaps the secrets of the peeper’s blood will one day help revive Ted Williams.

One particularly interesting thing I learned about peeper calls while investigating the “Fall Peeper” is that male and female peepers hear differently. The female’s hearing is tuned to the sounds made by males, which project over great distances; males can barely hear themselves. Studies show that the female peeper seems to prefer loud, fast calls. The female can also hear more males when they’re singing from elevated positions, such as in trees. The odd peeper we hear now, making noise for reasons other than trying to attract a mate, is most likely singing from closer to the ground. It’s warmer down there, and safer. Even the tree frog, which will also call sporadically this time of year, has undoubtedly moved down the trunk before sending out its short trill.

I still can’t help but wonder, though, what they’re going on about. The Spring Peeper isn’t a social creature, so these are not like the contact calls of bird flocks. A naturalist friend suggests that maybe the frog’s responding to the fact that the photo-period, the length of daylight, we’re experiencing now is similar to that of spring. Or perhaps its late season peeps, repeated here and there throughout the autumn-hued woods, are its last expressions of vitality before being literally frozen silent for the winter. It responds to the ebbing warmth of the dying season by giving voice while it still can, because it can—the last hurrah of the singing frog.

Kristen Lindquist is an amateur naturalist and published poet who works for Coastal Mountains Land Trust in her hometown of Camden.