Around the Mediterranean: an extreme example of loop migration in a long-distance migratory passerine

An important issue in migration research is how small-bodied passerines pass over vast geographical barriers; in European-African avian migration, these are represented by the Mediterranean Sea and the Sahara Desert. Eastern (passing Eastern Mediterranean), central (passing Apennine Peninsula) and western (via western Mediterranean) major migration flyways are distinguished for European migratory birds. The autumn and spring migration routes may differ (loop migration) and there could be a certain level of individual flexibility in how individuals navigate themselves during a single migration cycle. We used light-level loggers to map migration routes of barn swallows Hirundo rustica breeding in the centre of a wide putative contact zone between the north-eastern and southern-western European populations that differ in migration flyways utilised and wintering grounds. Our data documented high variation in migration patterns and wintering sites of tracked birds (n = 19 individuals) from a...