Birds fly in a V formation, or in echelon, because it saves effort. Much as bicycle riders in a group can save as much as 30% over the effort needed by a single rider, the birds in the V take advantage of the eddies created by the wings of the birds ahead of them . There have been tests for flying fighter jets in similar close formation to extend their range, but the ability of the pilots to maintain the needed tight spacing for several hours without interruption was not sufficient.