It has long been suggested that carrier pigeons followed man-made structures, such as highways and railways, during their trips. This theory has now been validated by a team of European scientists. They equipped 216 pigeons with GPS devices and followed their flying paths by satellites. They studied the behavior of these homing pigeons during trips varying from 20 to 80 kilometers in an area around Rome, in Italy, between 2001 and 2003. In "Putting GPS to work, researchers shed light on road-following by pigeons," you'll learn that "the birds appeared to follow roadways was strongest in the early and middle sections of their homeward journeys, when, the researchers suspect, roads serve to stabilize the birds' innate compass course." The researchers speculate that by following highways they 'remember,' the pigeons have more time to watch for predators.
Here are some details about the experiments.
Anecdotal evidence from breeders of racing pigeons as well as initial aerial tracking studies together suggested that pigeons may follow roadways and use highway landmarks as turning points in their flight. However, the challenge of accurately tracking the birds stood in the way of solid quantitative analysis. In the new work, miniaturized GPS "flight-loggers," which pigeons carried on their backs, allowed researchers a clear and reliable picture of the birds' flight paths.
Over three years, the researchers analyzed more than 200 flight paths of 20-80 km in length made by pigeons travelling toward their home loft from numerous release sites located in the general vicinity of Rome, Italy. They found that, when released from familiar sites, pigeons with homing experience were significantly attracted to highways and a railway track running in the approximate directions home. When these structures began to veer significantly from the beeline to the loft, some birds tended to break away and head in a more homeward direction, but others took a detour by following the highway until a main junction, at which point they followed a valley road in the direction of the loft.
So what are the benefits for the pigeons to follow roads which can lead to longer trips?
The researchers found that, although following roadways in some cases represented significant digressions from the beeline home, in general the early benefit of the roadways in keeping the birds on course seemed to compensate for the added flight distance. In fact, the birds appeared to prefer to follow roadways once they became experienced with the release sites; individuals who made three or more journeys home showed an increasing tendency to follow highways. The authors speculate that the preference for roadway following could form because easier navigation may allow brain processing-time and power to be directed to other tasks, such as watching for predators.
The research paper has been published by Current Biology in its July 27, 2004 issue, under the title "Pigeon Homing along Highways and Exits."
||This map, coming from the paper listed above, shows the tracks (in red) of 216 GPS-Equipped pigeon flights near Rome during 2001–2003. Green lines show GPS tracks obtained by a car. (Credit: Lipp et al.).|
Scientific American published a brief story on the subject, "Highways Help Pigeons Find Their Way Home." It contains a photograph of a GPS-equpped pigeon.
Sources: Cell Press news release, via EurekAlert!, July 26, 2004; Current Biology, Vol. 14, Pages 1239-1249, July 27, 2004; Scientific American, July 27, 2004