Reverse migration
A phenomenon in which birds fly in a direction opposite to that which they would be expected to take during a particular migration. It is possibly caused by instinct causing an inappropriate reaction to some factor of the environment. Reversed migration may bring to the British Isles in autumn migrants from eastern Europe which should have flown south-eastwards, for example the Arctic Warbler Phylloscopus borealis and the Red-breasted Flycatcher Ficedula parva.From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver