Birds “hear” the weather.

In our previous two posts we revealed how migrating birds use barometric pressure to clue them  in on weather conditions, and how they use those meteorological cues to take advantage of oncoming weather to jet them over really long distances. Back-filling in here a little bit: Weather is predominantly driven by a couple of interacting global variables: Differences in pressure, and differences in temperature. These variables are locked into how much moisture the atmosphere can hold under terms like “Dew Point” and “Water Vapor Pressure.”

 

So while meteorology (weather prediction) is informed by observations of clouds, thermometers, anemometers (wind speed), and barometers (atmospheric pressure), it can be broken down into to study of the geo-spatial interactions of atmospheric pressure and temperature.

 

And in the same manner that things that drive the waves, swells, and surface textures of the ocean (wind, currents, thermal gradients, and ocean floor features), the ocean of air above us is similarly driven. We see the complex and beautiful expression of this in the clouds.

 

An extremely simple example of how this works is when the sun warms up the land adjacent to the ocean, the heat rising up from the land creates a low pressure zone adjacent to a higher pressure zone over the ocean. So the higher-pressure ocean air flows (or rushes) into this low pressure field, creating onshore winds (or hurricanes). This interaction is so dependable that offshore wind farms make sense in terms of reliable wind.

 

Given that weather and wind have a strong bearing on the successful flight plans of migrating birds, it would make sense that these critters would have evolved “meteorological adaptations” to sense these variables.

 

And they have. Much like how our eardrums translate high frequency pressure oscillations in the air into “sound,” migrating birds have organs that translate the much lower frequency (infrasonic) atmospheric pressure oscillations into the information they need to predict the weather.

 

There may well be other infrasonic variables that help migrating birds orient along their routes. Wind blowing across ridge-lines may act like the fipples of  giant flutes; waves crashing on beaches might sound like giant tympani; ocean swells would oscillate long parallel Microbaroms – all providing really long wavelength acoustical cues that would help birds hear where they are – and know where they are headed.

 

Of course this can only remain “informed speculation” because the usual way of determining perception and response would be to surgically remove or scramble their perception and find out if it interferes with their performance. This is becoming more ethically questionable, but also due to the geographical scale, difficult to execute and observe.  This we will explore in our next post…
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