The Best American Science and Nature Writing 2010 by Tim Folger

Author:Tim Folger [Dyson, Freeman]
Language: eng
Format: epub
Publisher: Houghton Mifflin Harcourt

Because low-frequency traffic noise accounts for most of humans' clamor, animals that use low-frequency calls and can't switch to higher frequencies are threatened most. Slabbekoorn says birds such as orioles, great reed warblers, and house sparrows fit this category. Populations of house sparrows are declining throughout Europe; researchers haven't pinpointed the cause, but Slabbekoorn suspects human noise is a factor.

Bernie Krause has witnessed a similar phenomenon among spadefoot toads in the Mono Lake basin east of Yosemite National Park. Using its big front claws, the toad buries itself one meter below the desert floor and can survive there for up to six years. When rain finally comes, the toad emerges and joins others to sing in chorus, which makes it harder for predators such as owls and coyotes to get a bead on where the sound is coming from.

The problem is that during nighttime periods when the toads do their singing, military jet planes often use the basin for training. Flying only one hundred meters above the ground, the planes are so loud that the toads can't hear each other. Even after the planes leave, it takes twenty to forty-five minutes for the toads to resume their synchronized chorus, and in the meantime they're vulnerable to predators. Krause believes the noise is partly responsible for a precipitous decline in spadefoot populations, which he has studied since 1984.

Even adaptable species may be altered in fundamental ways. For instance, if changing calls or switching frequencies helps male birds be heard, they could earn an advantage when it comes to attracting female mates. Over time, this dynamic could force evolutionary changes, splitting populations of birds into localized species with specialized reactions to the sounds in their vicinity.

Slabbekoorn and his colleague Erwin Ripmeester think these noise-driven evolutionary forces may already be separating European blackbirds into urban and rural subspecies. The two researchers have even begun testing whether rural birds can recognize their urban brethren's hip new calls. If Slabbekoorn and Ripmeester's hunch is correct, it could mean that humans, already powerful conductors of the material world, may be extending their fierce control to the audible one.

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