Considering we do not know exactly how a bird has the ability to home and bearing in mind taking a bird hundreds of miles from it's home and releasing it is in no way natural, Pigeons like most birds only fly to find food
The world is expanding in all directions due to technology especially with radio signals, mobile phones, Fm signals and wireless computers so the chip on the leg may be the final straw IF the birds depend on this to home, untill we find out then we are only guessing
One thing for sure any predator will spook birds and send them in all directions totally breaking any confidence they have to try it again :-/