MIGRATORY PATH AND GENES. “Many components of migratory behaviour, such as the amount, timing and intensity of migratory activity, are under strong genetic control, at least in small night-migrating passerines. Also cross-breeding experiments among groups of European blackcaps (Sylvia atricapilla) that differed in migratory behaviour indicated a strong genetic basis of this behaviour.”
http://rspb.royalsocietypublishing.org/content/early/2011/02/11/rspb.2010.2567