Understanding complexity of the migratory phenotype in Palearctic–Indian migratory buntings: connecting molecular dots from laboratory studies

Abstract

Avian migration has been studied for a long time. Yet, very little is understood about the mechanisms underlying the preparation and departure of these migrants twice-a-year towards their destination. In recent years, some experimental evidence is accumulated from studies on the Palearctic-Indian migratory blackheaded buntings Emberiza melanocephala and redheaded buntings Emberiza bruniceps. These are obligate latitudinal migrant passerines, with yearly to-and-fro migrations between breeding grounds in west Asia/southeast Europe and overwintering areas in India. The migratory voyages are not isolated seasonal events; rather, they are part of the overall annual itinerary closely coupled to the reproduction. This review focuses mainly on the studies that have been carried out for more than four decades on these two buntings. We will outline first the characteristic traits of the anticipation, preparation, beginning and maintaining the migratory flight. The subsequent sections summarize briefly the molecular mechanisms underlying fat fuel accumulation, and changes associated with the phasing of the activity and rest periods within 24-h day during the nocturnal flight and daytime stopovers. In addition, we discuss mechanistic differences between the onward (to wintering areas, autumn migration) and return (to breeding grounds, spring migration) migrations. The two seasonal migrations differ in the context, physiological states that birds are in prior to each migration, and surrounding physical environment (photoperiod, temperature, food availability) that birds encounter during the migration period. The final section on perspectives presents an ecological and societal relevance of avian migration research.