Vagrancy in Birds

There is a prevailing idea among those who study vagrancy that vagrant birds have made some sort of mistake. Either they are genetically defective, and therefore they orient in the “wrong” direction, or they are “blown off course by the wind.” Certainly it is remarkable the distance traveled by vagrant birds (and this book highlights many of the most extreme examples) but the basic notion that there is something “wrong” with birds that do this requires more critical examination. Typically, birds disperse during the years prior to breeding, and the majority of long-distance vagrants are juveniles or at least pre-breeders. Species or populations of birds do tend to orient in particular directions while dispersing, but there are very large variations about the mean direction, so that many individual birds normally orient in different directions from the mean direction followed by most of their population. Similarly, probability distributions of distance dispersed...