In Northern New England, seasons aren’t always clear-cut. We have mud season, spring, summer, fall, second mud season, and winter. Our two mud seasons have many similarities; leafless trees, golden brown vegetation with patches of green interspersed, and huge ruts down dirt roads that have as much say over what direction your car is going than you. The spring mud season is usually worse, as the melting snow brings much greater potential for flooding and washed out roads. Yet, that first mud season also brings life to the forest by filling vernal pools with water, the preferred breeding habitat of many woodland frogs and salamanders. Every wet spot in the state resonates with the chorus of Spring Peepers and Wood Frogs, 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 phantom peeps. As spring turns to summer, the peepers die down, other species of frog pipe up, and by August the frogs are pretty much done. Yet, when fall rolls around, on cooler or wetter days, a familiar sound re-enters the forest. You weren’t confused, that sporadic “peep…. peep…. prrrreeeep…” probably was a Spring Peeper.
I am often asked by friends, including perplexed birders, if I know what that peeping sound coming from the trees in the fall is. Even people familiar with the call of the Spring Peeper have a hard time identifying them out of context. Adding confusion to the matter, peepers in the fall are usually making their vocalizations from dry woodland settings instead of the wetlands where they breed, and folk just don’t expect to hear any frogs so late in the year, so it’s easy to assume that new woodland song is some weird bird passing through. So why do Spring Peepers call in the fall?
Why Spring Peepers call in the fall at such northern latitudes isn’t exactly 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 first few days after conditions start to warm back up. By the time these frogs are about to hunker down for the winter, 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. Their systems will entirely shut down 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. Not all are inspired to call during spring-like conditions in the fall, so you are unlikely to hear a strong wetland chorus, but rather just a sporadic peep here and there, which you will sometimes hear in the winter if the frogs “wake up” on warm days 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 our northern Spring Peepers calling in the fall could also stem from an innate drive to breed all winter; a compulsion that is only interrupted by freezing temperatures. On at least a few occasions, during warmer wetter years, we have received reports of large Spring Peeper choruses calling from wetlands after September in Vermont, 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.