We live on an ever more-populous planet, pulsating with human-generated noises of every description. As the din of humanity grows ever louder, what will this mean for wildlife?
It's an important question. Across the U.S.A., for example, nearly nine-tenths of the population experiences artificially elevated sound levels. In the world's oceans, noises from commercial shipping alone have risen an estimated 16-fold in recent decades.
The most ubiquitous noise-making structures humans create are traffic-laden roads, which already crisscross the Earth and are projected to increase in length by some 25 million kilometers by mid-century—enough to encircle the planet more than 600 times.
A recent study by Heidi Ware and colleagues used an innovative ‘phantom road’ to assess how road noise affects migrating bird species.
Working in Idaho, USA, the authors laid out an array of loudspeakers to mimic road sounds, which they turned on and off periodically to judge the birds' responses. They also captured birds using mist-nets to assess their overall body condition.
The authors found that bird abundance declined by about a third near the phantom road, with some some noise-sensitive species avoiding the area.
In addition, even birds that remained near the phantom road often fared poorly, having lower body weight and worse overall condition than birds captured elsewhere.
The authors attributed this to the fact that the birds were often startled by sudden road noises -- and so spent more time looking around for predators and less time feeding.
This is particularly bad news for migratory birds, which are already stressed out by the huge exertions of migrating vast distances. More noise disturbance could mean that more birds will starve to death while trying to migrate.
In an independent perspective piece on this article, ALERT director Bill Laurance emphasizes that the rapidly expanding footprint of roads and other infrastructure across the planet is invisibly degrading habitat quality for noise-sensitive species.
Laurance suggests that many kinds of species could be affected by human-generated noises.
For instance, might sensitive marine species, such as echolocating whales or migratory fish, avoid noisy regions such as high-volume shipping lanes or areas where naval vessels regularly pierce the oceans with high-intensity sonar?
Could echolocating bats be distressed by roaring airplanes or even by the steady whine of wind farms or other infrastructure?
The findings of Ware et al. suggest that human-generated noises can be serious stressors for some wildlife. This is an alarming prospect in a world ever more beset by human-induced noises.
For instance, nowhere in Costa Rica’s iconic La Selva Biological Reserve can one avoid hearing the incessant thrum of a nearby highway. Many other nature reserves are suffering a similar fate, underscoring the urgency of limiting new roads in protected areas and devising strategies to limit noise disturbances where roads already exist.
For wildlife and for humans too, quiet places on the Earth are becoming increasingly rare and precious.