Using age-ratios to investigate the status of two Siberian Phylloscopus species in Europe
Distinguishing between vagrancy and regular migration has proved to be challenging as vagrants may, in theory, act as pioneers in the establishment of new migration routes. Because migratory songbirds tend to follow the same orientation and migration route throughout their lives, age assessment can help to distinguish individuals which have already used a route (i.e. adults) from those using it fo
