The Subtle Sounds of Summer

For months, the two-inch Sierran treefrog sang alongside rival males in his breeding pond, enticing females with a thousand kreck-eks. As summer arrives, the pond dries and his breeding job is complete; his offspring are already growing froglet legs. In search of more private dampness, he creeps away to an empty corner in a planter pot. It’s a fine spot for his bachelor months, and he brushes off his land call: a long, single-syllable cr-r-r-eck. This time, he performs as a soloist. 

The little amphibian had a serendipitous audience member: Jack Hines, a musician, soundscape ecologist, and host of the Ear to the Wild podcast. His Sonoma County backyard was our frog’s opera house. 

Hearing can lead to learning, Hines says, “if one is inquisitive.” The attentive listener will find that the shift from ensemble to soliloquy is characteristic of summer soundscapes, as the mating-time racket eases. The dawn chorus tapers off; the brains of singing birds start to prune away the extra song neurons they grew during breeding season. “Summer has more of a gentle tone to it,” says Tony Passantino, education program manager at the Sonoma Ecology Center—of susurrating dry grass, the distant caws of crows, an acorn woodpecker’s hammering. 

If spring is an auditory buffet, summer is a tasting menu for the subtler palate. There’s the upslurred tweet of the western flycatcher, the abrupt umpire’s whistle of ash-throated flycatchers. Cicadas live their entire adult lives in a few months, crackling in the trees; August and September are peak months for cricket orchestras and insect life in general. 

These are the pleasures of a summer ear. They’re also, for a growing field of soundscape ecologists, data. The acoustic fingerprint of an ecosystem can track migration shifts, disappearing species, changing weather. During California’s recent droughts, Passantino learned that when a creek goes dry, “you have a cascading loss of sound” around it. Ecologists listen for both “biophony” (sounds made by nonhuman organisms) and “geophony”—non-biological natural sounds like running water, howling wind, or the low grumble of a shifting fault line. Deciding where to record, Hines says, is like evaluating the acoustics of a concert hall: “What seat do I choose?”

The recording technology is important too, partly because many sounds exist beyond the threshold of human perception. Hundreds of thousands of Mexican free-tailed bats migrate to the Bay Area every summer, using high-frequency sound waves to pinpoint prey. Most of their tactical pings are inaudible to our ears, but you might catch a few mousey squeaks. Bats produce the piccolo tones of the summer orchestra with a specialized larynx, hardened almost into bone to withstand rapid-fire vocalization.