People have used homing pigeons to carry messages across long distances since Babylonian times. But how the birds find their way home has remained somewhat of a mystery. Top theories included both a keen sense of smell and the ability to detect magnetic fields. Now, after decades of trying, scientists have proven that pigeons do in fact possess magnetoreception--a potentially important navigational cue.
In the study, biologist Cordula Mora, currently with the University of North Carolina, Chapel Hill, and colleagues put homing pigeons into a tunnel. A magnetic coil on its roof generated a magnetic field that peaked in strength at the tunnel's center when turned on. Mora trained four homing pigeons to perch on one side of the tunnel when they sensed the field and the other side when the field was absent. The pigeons chose correctly between 55% and 65% of the time in 24 tries.
Previously, researchers had found magnetite crystals in the upper beaks of pigeons. To determine whether this region is the seat of the birds' magnetic sense, Mora attached tiny magnets to each pigeon's beak to impair its field detection ability. The birds' test accuracy plunged below 50%, then improved as they acclimated to the disturbance. Attaching nonmagnetic brass to their beaks did not impair their accuracy, however, nor did snipping the olfactory nerve leading from this area.
The findings, published in the 25 November issue of Nature, bolster the theory that pigeons can map their positions by tuning in to the magnetic fields encircling the globe. "Every point on Earth has a unique combination of magnetic intensity and magnetic inclination," Mora says. "This would help the pigeon know where it was in relation to its goal."
Other researchers say the discovery is a big step forward in understanding the homing pigeon's sensory systems. "Many people have tried in the past to condition birds to detect magnetic fields, and this is the first that has convincingly succeeded," says Henrik Mouritsen, a neuroethologist at the University of Oldenburg, Germany. However, he points out that the magnetic field in the experiment was many times stronger than anything found in nature. Nor do the findings rule out smell as a navigational cue, says physiological ecologist Martin Wikelski of Princeton University. The birds could still rely on smell to navigate in some places, he says, and use magnetic fields in others.
More about the role of magnetoreception in animal orientation, from the University of Illinois, Urbana-Champaign
An article on pigeon navigation credited to Cornell University
Cordula Mora's home page