That is Not the Sound of One Hand Clapping!

There I was, leaning back in my recliner, legs stretched out, hands behind my head, starting to drift off into nap-land. Then my brain took a left turn and started thinking about the effects f sound – noise really – on people’s ears. It started with my thinking about my own loss of the higher frequency parts of my hearing, then shifted to thinking about a friend of mine that did a series of biological surveys along the main LAX runway. All sorts of big, loud jets coming and going regularly. My friend claims that he has lost virtually all of his high-frequency hearing. That’s too bad, too because he had really great hearing when we were young. He could hear the lower end of the calls of spotted bats, which produce frequencies right at the edge of human hearing. Of course, thinking about the spotted bat calls got me to wondering about what the impacts of loud sounds – noise – are on critters other than people.

Some folks are concerned about underwater noise impacts on the physiology and biology of marine animals, especially whales and dolphins.  They cite noise from boats, sonar, oil exploration explosions, and similar sources. However, I have heard a lot less about the potential impacts of terrestrial noise.

I know there are studies on the effects of off-road vehicle engine noise (loud pipes – motorcycles) on kangaroo rat hearing. Kangaroo rats’ hearing is sensitive to very low frequency, low amplitude (faint) sounds. Apparently, kangaroo rats can hear the sound made by owls wings in flight.

There is evidence that birds have to modify their songs to accommodate urban noise. Urban noise is affecting breeding success in some bird species. I wonder if anyone has studied the impacts of urban noise on bat foraging behavior? When I was a young person, I observed that if I whistled loudly and shrilly the bats foraging around streetlights in my neighborhood would respond. When I whistled, they would make abrupt turns in their flight – they would jink. The response was very predictable, and I used to do it whenever I wanted to impress someone with my arcane knowledge of biology.

Another friend of mine was doing a biological survey on the Air Force bombing and gunnery range near Las Vegas. He and his partner were contracted to do the studies for the Air Force and had explicit permission to be on the range. There were not supposed to be any flights or training exercise that day. As they were working, an aircraft flew over at near ground level and going somewhere above Mach 1. The resulting sonic boom deafened the pair for several hours afterward. They recovered, but I have to wonder what the effect was on the critters that live in and on the ground. Snakes have no ears, but they can sense ground vibrations. Could such a low-level sonic boom cause sufficient ground vibration to affect them? Lots of lizards and rodents also live in the desert there.  Would they be deafened – temporarily – permanently? Would the kangaroo rats lose their ability to hear their predators approaching?

If exposure to aircraft noise along a major runway damaged my friend’s hearing, what might it do to the biota along the runway? My friend was there on several occasions, for several hours each. The local critters are there 24-7-365. What happens to the critters’ community organization when auditory signaling no longer works? I wonder if whales and dolphins will have to learn sign language?

I have no answer to my questions. Biologists studying the impacts of noise are only beginning, I believe, to understand some of the ramifications of noise on our ecosystems. I guess sound is just one more of the insults that humanity is heaping on non-human systems as well as on our own.


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