Tracking migration of black-headed buntings Emberiza melanocephala reveals the Iranian Plateau as an ecological barrier along the Indo-European flyway

The black-headed bunting is one of the few species that migrate along the Indo-European flyway, and its migration routes and phenology are poorly understood. We provide the first individual-based year-round tracking study describing route choice and timing of black-headed buntings migrating from a breeding site in Croatia to a 6000 km distant non-breeding region in Maharashtra, central India. To evaluate landscapes important for the black-headed bunting migration, we quantified land covers and climates along the migration corridor. Stopover areas during the post-breeding migration were concentrated in four distinct regions: the Balkan Peninsula, central Anatolia, along with the Zagros mountain range and from the Indus river delta to the Kathiawar Peninsula. Post-breeding migration routes followed the shortest path connecting breeding and non-breeding sites, except for the initial detour from the breeding sites to the first stopovers at the Balkan Peninsula. The pre-breeding migration routes occur along the Arabian Peninsula, about 1000 km south of the post-breeding routes – creating a clockwise loop migration pattern. Post-breeding migration lasted about two months, whereas pre-breeding migration was almost two times shorter, conforming to energy- and time-minimisation strategies, respectively. During the post-breeding migration, birds seem to track ecological niches found on their breeding grounds. Post-breeding stopover areas were rich in mosaic lands and were in warm and dry climates of Mediterranean character, while forests and bare areas, as well as arid and humid climates, were avoided. Based on distinctly scarce and widely dispersed stopovers and high travel speeds over the Iranian Plateau along with prolonged stopovers before and after the Plateau, we identified the Iranian Plateau as a major ecological barrier for buntings and likely for other species migrating along the Indo-European flyway.