Via nouvo.ch, an curious project carried out by Hans-Peter Lipp. They studied pigeon navigation using small GPS attached to the birds.This led them to "the best evidence yet of pigeons following roads" as reported by science week:

The authors present an 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 authors suggest their 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. .