Migration routes and wintering sites of the Aquatic Warblers Acrocephalus paludicola breeding in Lithuania and North Belarus

For the effective protection of the globally threatened Aquatic Warbler in its entire range, knowledge of the migration and wintering areas as well as their current conservation status is of great importance. The question on where the different breeding population overwinter where (connectivity) equally important. This is also essential when new breeding populations are re-established in restored breeding sites through translocation from other, distant areas, as recently performed in Lithuania. From previous geolocator studies in central Ukraine and south-western Belarus, as well as from ringing data, it was known that these populations overwinter in Mali (Inner Niger Delta IND) and southern Mauritania. In addition, at least some birds of the NE-Polish breeding population overwinter in the Senegal delta (ring recovery). In 2018 and 2019, the migratory routes, stopover and wintering sites of two breeding populations at the north-western distribution range border in N-Belarus (29 males) and Lithuania (31 males) were investigated using light-level geolocators. All 19 recovered data loggers recorded almost complete annual cycles from mid-July to at least early April. Migration and overwintering sites of both populations did not differ significantly. Most (16 out of 19) birds also spent the winter in the Inner Niger Delta and surrounding wetlands within and around Mali. Only one bird from Belarus hiberbated in the Senegal Delta. One of the Lithuanian birds overwintered in northern Burkina Faso, another northern Nigeria. In addition, important details about the course of migration routes, timing and resting areas could be obtained. For example, the outstanding importance of Morocco and northern Algeria as resting areas on spring migration became obvious. The investigations applying geolocators resulted in a very complex and differentiated picture of the migration and stopover pattern of adult male Aquatic Warblers.