Songbird migration between Eastern Europe and Southern Asia: how to deal with the arid belt?

The arid belt of Central Asia constitutes a barrier for small landbirds during autumn migration. Some species that migrate from Siberia to Africa circumvent this barrier by taking a detour around the northern coast of the Caspian Sea. It becomes increasingly clear that at least some songbirds that migrate between eastern Europe and southern Asia also perform a detour along the northern edge of the desert. Trapping data from the northern fringe of the barrier collected in this study (Orenburg Region of Russia, 51° 22′ N, 61° 23′ E; September 2023) and from earlier studies performed west and east of our study site show that some songbirds that migrate from European breeding grounds towards south and south-eastern Asian wintering quarters make a direct crossing, whereas others make a detour and circumvent Central Asian deserts. Ecological differences between the species of migrants cannot explain the observed pattern. Those species that make a detour are the ones that are considered to have colonized Europe from their ancestral breeding areas east of the Ural Mountains most lastly.