Calls From Within A Couple Of Meters

I am immersed not only in the manifestations of life’s diversity but in the experience of life’s ongoing creativity. The overwhelming press of sound and other senses here is one of evolution’s most powerful generative forces. The ringing cuts through the rumble of traffic from the town’s bypass road and the sputtering growl of a small airplane. I’m standing in the suburbs of Ithaca, a small town in upstate New York. When I first started visiting these woods, three decades ago, I was a recent immigrant from northern Europe, and the winter seemed to me dispiritingly long. Here chill, gray days keep a firm lock on outdoor life until well into March. The season of migrant songbirds and spring wildflowers does not start in earnest until late April. On windless days, only the gentle palaver of chickadees or the drumming of distant woodpeckers enlivens the air. I approach the forest and the merged quality of distant sound clarifies into thousands of individual voices. Each frog gives a sharp peep, a pure tone, rising slightly, lasting about a quarter of a second. Mingled among these are longer, raspy calls, reeep. I pad along a boardwalk through the swampy woods, moving slowly so that I do not startle and silence the singers.

Beyond The Limit

Inside the chorus, the sound pressure level is as loud as the blast of a radio turned up high. Visiting amphibian choruses in the springtime has become a ritual that lifts me out of winter’s despondency. The frogs bathe me in sound. I feel as if every cell of my body is shaken into wakefulness by the force of their voices. I suffuse my body with the energy of a reawakening Earth. Another winter ended. It is perhaps a measure of how unattuned my senses were to the ecological rhythms of North America that the frogs sometimes brought me to relieved, grateful tears. Something inside me could not believe that the long gray cold would end, anxiety enhanced by geographic displacement. Now, after thirty spring seasons on this continent, the smiling relief still comes every year. I’ve also learned to hear more nuance in the amphibian choruses. The rich woodlands of eastern North America are home to more than three dozen species of frogs and toads. Every species has its habitat and rhythms.

Sailing To The Moon

Eastern spadefoot toads give their choruses of explosive waas for a couple of nights only, after summer thunderstorms. It is not just the experience of time that changes as we listen to the voices of other species. Through the varied sounds of frogs and toads, and those of birds and singing insects, travel becomes an education in the complex geography of life. We humans seem to do our best to impose uniformity on the land, but the tree frogs and song sparrows calling from behind the parking lot or along the edge of the subdivision speak of the complexities that we smother. Every forest or wetland has a distinctive combination of species. Amphibian calls did not, of course, evolve to bring joy or edification to humans. Sound making mediates breeding, territoriality, and the alliances and tensions of animal social networks. Every species has its own ecology and history, resulting in behaviors and voices particular to each. Much of the sonic diversity of the world, then, is rooted in the divergent social lives of animals. Standing on the boardwalk, I flip on a small flashlight, holding it inside a translucent red plastic water cup. Frogs have good night vision and can distinguish green and blue in gloomy light that is, to our eyes, a smear of gray. They’re less sensitive to red, though, and they keep calling as I pass my dim beam through the tangle of wet vegetation around me.

Its A Mean Old World

At least ten frogs call within a couple of meters of me, but I see only one. He is perched on a partly submerged stick, his head angled up by extended skinny forelegs. Under his chin, thin, partly transparent skin balloons, a wobbly bulb almost as big as the frog. As I watch and listen, his flanks pulse inward and, a split second later, the sac expands with a peep. The frog is about as long as my thumbnail but, at close range, the sound smacks my ears. Another push from his flanks and the call comes again, repeating once every two seconds. The peeper calls by jabbing a slug of air from his lungs over vocal folds in the windpipe. The throat sac receives the blast of sound and puff of air. The sac’s extended skin broadcasts the call in all directions. The elasticity of the air sac then pushes air back to the lungs, allowing the frog to call again without opening his nostrils to inhale. Amphibians lack ribs and diaphragms, and so they push the air with bands of trunk muscles whose bulk makes up 15 percent of a male frog’s body weight. His body is only two and a half centimeters long, covering an area of just four square centimeters. By calling, the peeper has extended his body’s presence in the forest by nearly twenty million times, not counting the sound’s vertical reach to listeners in trees. By allowing animals to find one another in complex environments, sound helps species to thrive where otherwise they would struggle. The peeper not only broadcasts his presence and location but also reveals his size, health, and perhaps individual identity. This information mediates social interactions at a distance. Rival male frogs space themselves in the swamp and reduce the dangers of bodily confrontation. Females not only find mates but assess them without coming close and risking either injury or disease transmission. When a female spring peeper emerges from her winter hideaway under the leaf litter, thawing a body that was steeped with antifreeze sugars, she listens for the bells that locate the breeding swamp. She likely also remembers the contours and aromas of the land, having lived in the forest, eating spiders and insects, for two or more years before maturing into a breeding adult. In other species, experimenters have shown that frogs have excellent spatial memory and navigation abilities, especially for breeding sites.