Windfarm noise above the waterline.

A bind of Sandpipers murmering

Mid-March of 2020 found us shutting down the whole operation. Many of us were cancelling business trips, and not commuting to work because a virus had taken center stage in all of our lives. I held on to our office for a while because I was the only one using it – and I found that because there were no cars on the streets, I could ride my bicycle to the office down the middle of the road.

These conditions lasted for some time, and the phenomena was dubbed “The Anthropause,” a global circumstance that seriously throttled back transportation, commerce, and almost every other activity in the land, air, and sea – except what came to be known as “essential work.”

Aside from the obvious reduction in human activities, I immediately noticed a few other things; the dawn chorus of the birds, which I had been missing for a couple of decades, became riotous. It was waking me up at 4am. I also noticed other thrilling bird behaviors: Robins flocking like warblers in tight formations; mumurations of starlings in town, and a generally relaxed, but acoustically in-tune behaviors of other passerine birds in and around my urban office space.

My first thought was that with no airplanes in the sky, the birds did not feel threatened by what they may have been reading as ‘raptor predators from above.’ But this didn’t explain the elevated dawn chorus activity.

What I have come to believe was that with the absence of trucks and cars thundering along all of the freeways and urban thoroughfares, the low-frequency, or ‘infrasonic’ noise field of the urban environment had significantly quieted down.

So why is this important?

It turns out that some birds use “infrasonic” energy to synchronize their flocking behaviors. The starling mumurations are one example, but you can witness this by watching any tightly synchronized bind of sandpipers or grain of sanderlings – as their white underwings flash in synchrony while darting over coastal waters.

Migrating birds need to sense “infrasonic” energy as a synchronized group, but also collectively for navigation. They need to know about oncoming weather, because they use the tailwinds of oncoming storms to push them to their desired destinations. If they take off too early, they end up “flying uphill” in unstable weather. And if they take off too late, they become buffeted by the torments of the storm.

One adaptation migrating birds have evolved is the ability to read shifts in barometric pressure, to determine when a weather front is just building up, or if it is the sincere onset of a storm – with the arrival of the tailwinds they need to assist their migration .

This was initially suggested by Douglas Quine, a fellow I spoke with decades ago regarding a paper he wrote on how homing pigeons read shifts in barometric pressure for navigation cues. By definition, these barometric shifts would qualify as “infrasonic,” and Dr. Quine established that pigeons could sense pressure oscillations at least down to 0.1 Hz  – one cycle over ten seconds (because that was the limits off his barometric test chamber).

So here is the clincher; of the many noises generated by wind turbines, one profound generator would be an infrasonic thumping that occurs turbine’s rotating blades intersect the stalled wind pressure that occurs in front of a turbine mast every few seconds. This infrasonic energy has caused a lot of contentions debate around terrestrial wind farms – where some people are highly disturbed by it… and others not.

There is a lot of energy in this blade thumping. And when there are hundreds-to-thousands of turbines generating this noise, how will it impact the navigation cues of birds who use infrasonic navigation cues? Particularly if the turbines are widely distributed along the “Atlantic Flyway” – the migratory route for zillions of birds who bind the Northern and Southern hemispheres together through their seasonal migrations.

I guess we’re about to find out…