With accuracy rivaling that of piloted airplanes, homing pigeons navigate thousands of miles of flight. Nobody knows their secret--it is almost as if they are reading a map. That may be exactly what they are doing, says geophysicist Jon Hagstrum of the United States Geological Survey. He believes the birds recognize landscapes by sensing infrasound, or very low frequency sound. Waterfalls, meteors, ocean waves, and winds whistling over mountains or through tunnels all generate distinctive washes of infrasound. Lab experiments show that pigeons are sensitive to such low frequencies, but results do not reveal why. Hagstrum claims that pigeons use the deep noises to build up elaborate mental topographic maps. Hagstrum looked at records of carrier pigeon races, in which thousands of birds are released all at once. Four races stood out because the birds returned hopelessly late or not at all. Each of these events coincided with nearby flights of the Concorde. The correlation led Hagstrum to the idea that sonic booms from the plane temporarily deafened the birds, knocking out a natural ability to picture and map the landscape in infrasound. Other animals might use the same technique. "This theory may explain how monarch butterflies, migratory birds, and whales navigate," he says. "Birds also react to something before major earthquakes, and I think it's infrasound." That may hold clues for humans about how to predict earthquakes.