Pigeon homing along highways and exits

Background- Anecdotal observations and early airplane and helicopter tracking studies suggest that pigeons sometimes follow large roads and use landmarks as turning points during their homeward journey. However, technical limitations in tracking pigeon routes have prevented proof. Results: Here, we present experimental and statistical evidence for this strategy from the analysis of 216 GPS-recorded pigeon tracks over distances up to 50 km. Experienced pigeons released from familiar sites during 3 years around Rome, Italy, were significantly attracted to highways and a railway track running toward home, in many cases without anything forcing them to follow such guide-rails. Birds often broke off from the highways when these veered away from home, but many continued their flight along the highway until a major junction, even when the detour added substantially to their journey. The degree of road following increased with repeated releases but not flight length. Significant road following (in 40%-50% of the tracks) was mainly observed from release sites along northwest-southeast axis. Conclusions: Our data demonstrate the existence of a learned road-following homing strategy of pigeons and the use of particular topographical points for final navigation to the loft. Apparently, the better-directed early stages of the flight compensated the added final detour. During early and middle stages of the flight, following large and distinct roads is likely to reflect stabilization of a compass course rather than the presence of a mental roadmap. A cognitive (roadmap) component manifested by repeated crossing of preferred topographical points, including highway exits, is more likely when pigeons approach the loft area. However, it might only be expected in pigeons raised in an area characterized by navigationally relevant highway systems.