“CLOCK POLYMORPHISM has been found to be associated with breeding in the blue tit (Cyanistes caeruleu) and migratory barn swallows (Hirundo rustica). Similarly, midday and midnight Ror-α and Rev-erb-α mRNA expressions have been found to vary with photoperiod-induced phenotypes in the night-migratory black-headed bunting (Emberiza melanocephala).”
http://www.fasebj.org/content/29/10/4248.full