How much do small-scale changes in flight direction increase overall migration distance?

During a radar study of autumn migrating waterfowl Denmark, individual flight trajectories of bird flocks were seen to show zigzag-like patterns, rather than exact straight lines. An analysis of these small-scale changes in flight directions, which are too small to be detected by satellite telemetry, showed that geese and common eiders Somateria m. mollissima were flying on average 0.7%, and 1.6% longer distances, respectively, than if they would have flown along exact straight lines. Thus, it is concluded that the flight paths are remarkably similar to straight lines. A multivariate regression analysis suggested cross wind as a factor increasing flight distance, and hence, the small-scale changes in flight directions could in part be a result of birds trying to compensate for wind drift.