Translocations are an increasingly applied conservation measure to recover animal populations threatened with extinction. Long-distant migrating passerines, however, have been rarely addressed in translocation projects so far. The globally threatened Aquatic Warbler Acrocephalus paludicola is a habitat specialist breeding in fen mires in Central Europe and wintering in sub-Saharan Africa. Local breeding populations experienced severe declines during the last decades due to habitat loss.
The aim of this pilot study was to reveal whether Aquatic Warbler will return to a distant release site and reproduce after wintering. The method is based on natal habitat imprinting of juvenile passerines before their first migration. In 2018 and 2019, 50 chicks (10 whole broods) each were relocated 600 km from Belarus to Lithuania at an age of about 7-10 days and hand-raised with predominantly wild insects captured in the surroundings of the release site. 99% of the chicks survived until soft release from outdoor aviaries. In 2019, 11 Aquatic Warblers (9 males, 2 females) were resighted at the release site after returning from wintering grounds. In 2020, 9 birds (6 males, 3 females) were observed, including 3 males from the 2018 release cohort. The intense monitoring in the subsequent years enabled us to estimate first year survival of juveniles. Local breeding population showed a substantially increase in numbers of singing males in 2020. This successful outcome gives new impetus for the restoration possibility of declined subpopulations of the Aquatic Warbler to halt the extinction at the western margin of the breeding range.