New theory for homing pigeon navigation
A researcher has found a new possible method used by homing pigeons when orientating their way home, called infrasound.
Jon Hagstrum, a geophysicist from the US Geological Survey in California, US, found that infrasound – ultralow frequency sounds – helps the birds to find their way straight back to their loft.
Hagstrum's theory is the first of its kind, with previous research suggesting that pigeons either rely on the Earth's magnetic fields or their sense of smell to reach home, unless either is affected and causes disorientation.
Growing up interested in pigeons, Hagstrum became aware of release-site biases and decided to investigate the matter of homing pigeon navigation. He looked at pigeon release data from three New York sites; Castor Hill, Jersey Hill and a site near the town of Weedsport.
Hagstrum found that the pigeons would repeatedly head off in the wrong direction from Castor Hill and Jersey Hill, rather than towards their loft at Cornell University. However, the same problem was only seen in young, inexperienced pigeons released from nearby Weedsport.
On other days, the pigeons would find their way back from the areas with no problem. Furthermore, homing pigeons released on the same days from the same sites, but who came from other lofts, could find their way home.
Homing pigeons are known to hear sounds as low as 0.05 hertz, which is low enough to pick up infrasounds at around 0.1 or 0.2 hertz, so Hagstrum mapped out these low-frequency soundwaves from Jersey Hill.
He found that, on an average day, the site sits in a "sound shadow" from the Cornell University loft. On a day with changing wind patterns and temperature inversions, infrasounds from Cornell reached Jersey Hill – the same day that the pigeons found their way back to the loft.
"I could see how the topography was affecting the sound and how the weather was affecting the sound [transmission]," said Hagstrum. "It started to explain all these mysteries."
The research has been published in the online Journal of Experimental Biology. Hagstram hopes to follow this up by finding out how large the pigeons' listening area is.
