I've heard of a hypothesis that proposed that the light colored tail
spots and markings on warblers (and other migrants) might be used by
the birds to follow each other in the night--kind of like tail lights on
a car. This would of course be dependent on flocking behavior. Is this
a crazy idea? In any case, isn't it interesting that so many migrants
have light colored spots on their tails?---other ideas?

--
David Bailey, psu03321 at odin.cc.pdx.edu