Silence is a rare commodity in the world we have created. Our senses are bombarded with all descriptions of sound to the point of sensory exhaustion. Likened to PTSD when violating a safe threshold, it may be time to find an escape.
Our avian friends are experiencing the same affliction.
As I was reminded on my early am canyon run, birds rely heavily on vocalizations to communicate. Lazuli buntings, warbling vireos, the barely audible blue-gray gnatcatchers added pleasure to my uphill slog. But not singing for me, rather to attract mates, defend their territory from rivals, and warnings for predators.
The excess racket that humans contribute prompt some species to sing at different times and in different ways. In Mexico, researchers found that house finches raised the pitch of their lowest song notes in response to road noise, and also held them longer. A study published in Current Biology examined song changes of the great tit across ten European cities revealed that in each location the birds omitted the low-frequency portion of their call.
However helpful such biological tricks may be for some birds, the nearer one gets to a densely populated town or city, the less diverse the avian community becomes. Not all species have the ability to work around the commotion.
House sparrows, which have a significant low-frequency component to their songs, have suffered population declines of two thirds in Great Britain over the past few decades. A University of Colorado at Boulder study found that mourning doves and black-headed grosbeaks avoid nesting near sites where natural gas is being extracted, as they cannot tolerate the noisy compressors. Blood tests revealed that levels of corticosterone in birds closest to the gas compressors were far lower than normal. This initially came as a surprise to the researchers, because corticosterone is the bird equivalent of cortisol — the hormone that prompts the human body to release a flood of adrenaline, increasing blood pressure, and jolting our brain with sugar. Only 21 different species resided in the noisy sites, compared to 32 in the quiet ones.
Many of us have grown accustomed to the hustle and bustle of the 21st Century, perhaps to our demise, but the birds may have a lesson to teach us about the value of peace and quiet: just how frighteningly little of it remains. According to an audio ecologist study, fewer than five minutes go by before the average patch of wilderness is interrupted by the sounds of human interference.
After years of recording the natural environment in places all around the globe, Gordon estimates that fewer than a dozen truly silent places are left. It is not just the birds that are vulnerable, either. The breeding success of some Australian frog species is being impacted by traffic noise, and ocean noise pollution caused by boat engines. Who knows what variety of species may be affected? Noise might seem an unlikely player on the ecological stage, but further study is definitely warranted on impacts of the anthropogenic racket.
Sound courtesy from Kevin Colver.