I have just seen an article in the most recent issue of BBC Wildlife Magazine and couldn't find mention of it anywhere else on the forum, so I thought I would put it here. Last year, fifty aquatic warbler Acrocephalus paludicola chicks that were between seven and ten days old were translocated from Zvanets wetland in Belarus (the largest habitat of the species) to Zuvintas Biosphere Reserve in Latvia. They were raised in captivity on-site before being released. This year, nine males returned to the new location and at least two females raised nestlings this summer. Because of the high success rate, another fifty warblers were released this July and the project will expand to include other countries. Most of the information for this comes from the BBC Wildlife piece, but there is an earlier news article here (it mentions the first returning birds and doesn't mention any successful breeding): The first ever translocation of the Aquatic Warbler is successful! - OTOP
An update on this project - the number of aquatic warblers seen in Zuvintas Biosphere Reserve in Lithuania this year is double the number seen in 2019. This is especially important, as large areas of habitat in Poland, Belarus and Ukraine were destroyed by fire. More information is included in the link below: Early success for Aquatic Warbler relocation project - BirdGuides