Between 1968 and 1987, about 900 homing pigeons released at the Jersey Hill fire tower in upstate New York got lost, never to be seen again. Why couldn't they find their way home?
Between 1968 and 1987, Cornell professor William T. Keeton and his colleagues released thousands of homing pigeons from different points in upstate New York and then tracked them to see if they could find their way home.
Homing pigeons are famously good navigators, and, for the most part, the pigeons set sail in the right direction. But there was one route that caused them trouble: A 74-mile stretch from the Jersey Hill fire tower back to their loft at Cornell. Only 10 percent of the pigeons trying to make that journey ever made it home. The rest -- about 900 pigeons -- disappeared completely.
Except, that is, on August 13, 1969. On that date, the pigeons released at Jersey Hill flew right back to Ithaca with no problems. Down on the ground, Keeton and his team took meticulous notes about the weather and whatever else they could notice. Nothing seemed different from any other day. They were mystified.
"When Bill Keeton was first setting up his pigeon loft at Cornell, he got birds from local pigeon racers," Jonathan T. Hagstrum, a geophysicist with the U.S. Geological Survey told me. "They told him: Don't go to Jersey Hill. You'll lose your birds."
There was something going on at Jersey Hill, but what? And why was August 13, 1969, so special?
Bird navigation is not well understood, and the hypothesized cues that birds use to make their "maps" (or how they point in the right direction homeward) are many: gradients in inclination and intensity of the geomagnetic field, visual landmarks, or even atmospheric odors. Keeton and his colleagues hoped that somewhere in that patch of upstate New York they'd be able to find something that was sending these pigeons astray. Whatever it was, it was likely a key component of pigeon GPS.
One possible clue: laboratory tests conducted in the '70s found that homing pigeons can detect what are known as "infrasounds" -- sounds at a frequency below the range of human perception. Humans, roughly speaking, can't hear sounds lower than 20 Hz, give or take a little for the sounds' intensity and the differing abilities of humans. (You can listen to a 20 Hz tone here.) Pigeons, it was found, could detect sounds at least as low as 0.05 Hz.
The world is downright awash in infrasounds. They can come from anything: explosions, earthquakes, storms. But the infrasounds that may guide birds come from one place: the ocean. The Atlantic Ocean, whose coastline is some 200 miles from Ithaca, New York, is banging against the floor of the deep sea, and that energy travels through the continent. "The East Coast is going up and down about four microns every six seconds," Hagstrum told me. The pulsing land acts like the cone of a stereo speaker, creating a pressure wave -- infrasound -- that birds would be able to hear. Additionally, another type of infrasound waves travel from the ocean through the atmosphere, not the land, and scatter when they hit mountains, buildings, and other vertical features of the terrain.
(Unlike the sounds humans hear, infrasounds can travel thousands of miles in the atmosphere. For example, a tone at 1000 Hz is 90 percent absorbed over a distance of seven kilometers at sea level. At 1 Hz, it takes 3,000 km to absorb 90 percent. For a tone at 0.01 Hz, "the distance exceeds the circumference of Earth," according to Hagstrum.)
An infrasound laboratory at the University of Hawaii captures examples of these infrasounds and then re-renders them into the range of human perception (20 Hz to 20 kHz) through methods such as pitch shifting and compression. Here, to give you a sense of this invisible-to-us sonic landscape, is one of their "infrasound" clips, this one of the surf on Moorea, an island in French Polynesia.