In recent years, anecdotal evidence had suggested that some pigeons were following highways when they were homeward bound. To test this theory, Peter Lipp of the University of Zurich and his colleagues outfitted a number of birds with miniaturized GPS devices that tracked their movements (see image). The researchers analyzed data collected from more than 200 flights (about 50 kilometers long) made in the vicinity of Rome over three years. They report in the latest issue of Current Biology that the animals were more likely to follow roadways in the early and middle sections of their journeys, even if this sometimes made their trips longer. The scientists suggest that the early benefits of staying on course can compensate for the increased distances. In addition, birds who became more familiar with a route by traveling it multiple times were more likely to use highways as guides compared with pigeons making the trip for the first time.
The authors note that homing pigeons appear to have a remarkable ability to shift from one home strategy to another, so the results may not hold true for birds on all their travels, especially those longer than 200 kilometers. But they posit that the birds might prefer following freeways--instead of using their innate compasses--because they make navigating easier and allow the animals to dedicate more brainpower to other jobs, such as keeping an eye out for predators.