Vagrancy of Yellow‐browed WarblerPhylloscopus inornatusand Pallas's WarblerPh. proregulusin north‐west Europe: Misorientation on great circles?

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Abstract
The migratory orientation of the two Siberian species Yellow‐browed Warbler Phylloscopus inornatus and Pallas's Warbler Ph. proregulus was tested on Christiansø, Denmark in the autumn 1994. We found an east‐west axis of orientation. Although weather and climate play an important role in determining actual survival of the vagrants, this axis fits well with the direction from the breeding areas to Christiansø. It thus suggests that misorientation may be an important factor behind the occurrence of Ph. inornatus and Ph. proregulus in north‐west Europe. Furthermore, it seems possible to explain the direction into Europe as part of a reverse great circle route, possibly arising because the birds do not reset their internal clock properly.