Up here in the often frigid Northeast Kingdom of Vermont, seasons are very clear-cut. We have mud season, spring, summer, fall, second mud season, and winter. That is a stark contrast from what I experienced in South Texas where it’s either hot and dry, hot and wet, or cool and wet (hot and dry being the norm). Consequently, our frog breeding seasons happen at roughly the same times every year, which cannot be said of many warmer environments where water rather than season tend to spawn amphibian reproduction. Here, as soon as winter melts away and temporary wetlands called vernal pools fill with water, every wet spot in the state resonates with the chorus of the Spring Peeper and the sound can be deafening. Indeed, stepping back into silence after a walk through the swamps in early April can leave your ears ringing with the sound of peepers. As spring turns to summer, the peepers die down, other species of frog pipe up, then by August it’s pretty much done. Yet, when fall rolls around, on cooler or wetter days, a familiar sound re-enters the forest; the occasional peep, peep, of some obviously confused Spring Peepers. (continue reading below video)
I am often asked by herpers and perplexed birders if I know what that peeping call is coming from the trees every fall. Even people familiar with the call of the peeper have a hard time identifying them out of context. This time of year most of the vocal peepers call from wooded uplands instead of the wetlands where they breed, confusing the matter further, and folk just don’t expect to hear any frogs this time of year. So why are they peeping now?
The exact answer isn’t known, but if you really think about it, it kind of makes sense. Spring Peepers are the first frog to breed when the snows melt. Because Spring Peepers are near freezing for months on end in the winter (sometimes freezing solid themselves), their metabolism is slowed so far down that they wouldn’t be able to fully enter a breeding condition during the winter itself. Instead, they get almost ready to breed in the fall, shut down for the winter, and finish the process in the spring. By mid-September, males are full of sperm and the eggs in females are almost as large and developed as they will be in the spring. Jim Andrews, who leads the Vermont Reptile and Amphibian Atlas, puts it like this; “Physiologically they are only days from spring breeding. Their systems will shut down entirely soon and they will need to be ready to breed immediately when they thaw out.”
Furthermore, conditions in the fall can be very similar to what peepers encounter in the spring. The days are short, air temperatures are cool, and there is a lot of rain. Water levels tend to be too low for the frogs to breed so instead of calling from the wetlands in large numbers, the fall peepers can be heard from the woods and usually in small numbers; just a sporadic peep here and there, which you will sometimes hear in the spring if the frogs wake up before suitable conditions arrive to facilitate massive migrations to the wetlands.
If you head farther south, where wetlands rarely ice over and winters are dominated by rain rather than snow, peepers do actually breed in the fall. In North Carolina, for example, peepers breed anywhere from November to April, so the frogs down there definitely need to be ready to take advantage of the rains by the end of September, so our northern Spring Peepers calling in the fall could be an innate compulsion to breed all winter; a compulsion that is only interrupted by freezing temperatures. On at least a few occasions, during warmer wetter years, we’ve even heard large Spring Peeper choruses calling from wetlands in the fall up here, though it is highly unlikely the eggs and young could have survived the bitter cold which followed shortly thereafter.
All things considered, we can forgive the Spring Peeper for its trespass into fall. Spring may be many months way, but for a peeper settling down for the winter, their big night probably feels like it is only days away, and they are ready for it.