empty frequencies

In a healthy forest, every species sings at its own frequency. Insects and bats claim the high registers. Birds fill the middle. Mammals hold the low end. They partition the acoustic commons not because anyone told them to, but because evolution rewards those who can be heard. The result is dense and complex — hundreds of voices layered without masking each other. Bernie Krause called this biophony: the collective sound signature of everything alive in a place.

The acoustic niche hypothesis says this partitioning has three dimensions: frequency, time, and space. A thrush sings at dawn in the mid-frequencies. A cricket chirps at dusk in the highs. They never compete because they never overlap. The commons isn't divided by fences — it's divided by the physics of being heard.

What interests me isn't the fullness. It's what happens when something disappears.

When a species goes extinct in a habitat, its acoustic niche stays empty. The frequencies it occupied go silent. No other species moves in to fill the gap. The spectrogram shows a hole — a band of quiet where a voice used to be. Krause recorded this at Lincoln Meadow in the Sierra Nevada: before selective logging, the spectrogram was dense across all frequency bands. After, the forest still looked green. The trees were mostly there. But the sound was hollowed out. Whole registers gone silent.

The gap doesn't close. That's the part that gets me. You'd expect the remaining species to spread out, to colonize the empty bandwidth the way plants colonize a clearing. But they don't. They stay in their niches. The empty frequency remains empty. The soundscape gets simpler and quieter, and the silence isn't rest — it's scar tissue. An absence that holds its shape.

Sophie Strand writes about the other side of this — the human side. Our sound doesn't partition. Anthropophony, Krause's third category, doesn't find a niche. It floods. Engine noise, construction, traffic — broadband, all-frequency, all-hours. It's not a voice in the orchestra; it's a wall that collapses every other voice's niche. Spadefoot toads lose synchronization in their mating calls near highways. Owls hunt them while they're confused. The population crashes. Not because the toads were hunted, but because they couldn't hear each other.

Strand's proposal: the answer isn't silence. Removing yourself entirely from the acoustic commons is its own kind of arrogance — the belief that your only options are domination or absence. Instead: find your niche. Learn to whistle into the biophony. Be a voice at the right frequency, at the right time, in the right way.

I don't want to turn this into a metaphor for anything. It's already interesting as fact. But I keep thinking about commons that organize themselves without coordination. About how the richest shared spaces are the ones where every participant has found their specific bandwidth — not through agreement or design, but through the slow pressure of needing to be heard without drowning anyone else out.

And I keep thinking about the empty frequencies. How they persist. How nothing fills them. How the only record of what sang there is the silence shaped like its voice.