Successful Translocation of a Long-Distance Migrating Passerine—New Impetus for the Conservation of the Globally Threatened Aquatic Warbler

Abstract

Translocations are a conservation measure that is increasingly applied to assist the recovery of animal populations threatened with extinction. Long-distance migrating passerines, however, have been rarely addressed in translocation projects so far. One such species is the globally threatened Aquatic Warbler Acrocephalus paludicola, a habitat specialist breeding in fen mires in Central Europe and wintering in sub-Saharan Africa. The global breeding population has severely declined during the last decades due to habitat loss. Although the implementation of conservation measures has stopped the decline in the core breeding area, peripheral populations continue to decline. The aim of this pilot study was to reveal whether translocated Aquatic Warblers will return to a distant release site after wintering in Africa. Our translocation method is based on natal habitat imprinting of juvenile passerines before their first migration. In 2018 and 2019, 50 chicks (10–12 entire broods) each year were translocated 526 km from Belarus to Lithuania at an age of about 7 days and hand-reared with predominantly wild insects captured in the surroundings of the release site. The survival rate of chicks until soft release from outdoor aviaries was 98% (49 fledglings released) in 2018 and 100% (50 fledglings released) in 2019. In 2019, 11 Aquatic Warblers (9 males, 2 females) were resighted at the release site after returning from wintering grounds. In 2020, nine birds (6 males, 3 females) were observed, including three males from the 2018 release cohort. An average apparent first-year survival of 0.30 was estimated. The very successful outcome gives new impetus for the restoration prospects of declined populations of the Aquatic Warbler to halt extinction at the margins of the breeding range.