By mid-March, birds like the Louisiana water thrush and the blue-headed vireo will be returning to the Great Smoky Mountains. They will have traveled hundreds of miles, mostly at night — perhaps across the Gulf of Mexico — from as far away as Central America, to their summer home in the Smokies.
The mystery of precisely how birds navigate on these epic journeys has never been completely solved. Plausible theories have included using the stars to navigate, using magnetic fields, watching landscape features like mountain ranges and coastlines, and their sense of smell. Now a new idea from Dr. Jonathan Hagstrum of the U.S. Geological Survey has the birding world chirping.
Hagstrum has noted that homing pigeons, the gold medalist of the avian navigational world, have amazing hearing. On the low end of the sound range, pigeons can hear down to .05 hertz, compared to humans who hear only to .20 hertz.
According to Hagstrum, if we could hear down to .05, we could hear some incredible things, like the sounds of ocean currents swishing along the seafloor, transmitted through the earth’s crust and atmosphere. Such sounds are pretty constant, and so could be used for orientation and navigation. And not just by pigeons, but possibly by other birds, whales, and sea turtles.
This revelation also comes with some responsibility. As you will read in the upcoming spring issue of the Smokies Guide park newspaper, researchers working in the Smokies are discovering that the world is becoming a pretty noisy place. In fact, Hagstrum’s theory was partially developed because sonic booms from jets once disrupted a popular pigeon race. So the loud sounds we humans make with our machines may be harmful not only to our eardrums but also to animals trying to find their way home.