The crow may fly in a straight line, but pigeons prefer the twists and turns of the open road. A new study finds that homing pigeons often follow large roadways, and even learn which exit leads home. The results provide clues to how birds navigate over large distances.
Homing pigeons have an internal compass that endows them with a general sense of direction. But scientists disagree about how much attention the birds pay to visual landmarks during the early and middle stages of long-range journeys. Some reports suggest that pigeons navigate by following major roads and other manmade objects, however technical limitations have made this hard to prove.
A University of Zürich team lead by Hans-Peter Lipp overcame these limitations by attaching miniature global positioning system (GPS) "path loggers" to the backs of 34 pigeons. The loggers tracked the birds as they flew home from release sites up to 80 kilometers away. The team reports in the 27 July issue of Current Biology that most pigeons followed highways leading in the general direction of their loft rather than taking a more direct path over the countryside. The researchers also observed that many of the birds waited until they reached a specific highway exit before changing course to complete their trip.As the birds repeated these journeys over a 3-year period, they relied on the highways more and more. "This suggests that road-following is a learned behavior," says David Wolfer, a co-author on the study. Once the pigeons realize the roads will lead them home, he says, they become more committed to them. Wolfer believes that reliance on visual cues such as highways and exits allows the pigeons to conserve time and energy that would otherwise be spent checking their bearings.The study proves that pigeons are very adaptable, says Charles Walcott, a neurobiologist who studies pigeon homing at Cornell University in Ithaca, New York. Although Walcott agrees that visual cues are important for pigeon navigation, he believes that longer flights should be studied. Pigeons are opportunists, he says, noting that the birds pick from a "Chinese menu" of possible orientation cues. "The only thing that matters to them is getting home."