In the spring of 2020, San Francisco went quiet. The parks were closed, the roads through them empty, and the low mechanical hum that had covered the city for decades drained away. Into that gap, a small gray-and-brown bird with a bold black-and-white striped head began to sing. It sang more softly than its kind had in years. And that quieter song reached other birds much further away than a louder one would have.
That is the heart of one of the most talked-about pieces of pandemic science, and it only makes sense if you picture two versions of the same city: the loud one the sparrows had adapted to, and the sudden quiet one that let them change their tune.
The loud city the sparrows had learned to shout over
White-crowned sparrows have sung in and around San Francisco for a very long time, and in recent history they have been singing over us. As traffic and other city noise built up through the twentieth century, the birds faced a basic problem: a rival or a mate couldn’t pick out their song from the background rumble. Low engine noise is especially good at drowning out low song.
The same research group that ran the 2020 study had already shown how the birds coped. In earlier work with George Mason’s David Luther, they found that city sparrows shifted their songs to a higher pitch to be heard above the city. That narrowed the range of notes they used and cost them some vocal quality. It worked, but it made the songs thinner and less impressive…