Expedition Solves Aquatic Warbler Mystery

Aquatic Warbler (photo: Dawn Balmer).

After five years of investigations, an expedition team has tracked down the wintering grounds of Europe's most threatened migratory songbird - the Aquatic Warbler - in Senegal.

"...knowing where they are in winter now provides a starting point to mirror the successful European conservation efforts in Africa." said Lars Lachmann of RSPB (BirdLife in the UK) who co-organised the expedition to West Africa.

The expedition discovered good numbers of Aquatic Warblers in an area of about 100 square kilometres within the Djoudj National Park, an Important Bird Area (IBA) in north-west Senegal. Preliminary estimates range from 5-10,000 birds at this single site.

Researchers from BirdLife International and RSPB combined state-of-the-art scientific analysis with traditional fieldwork to unravel the mystery surrounding the warblers' unknown wintering sites.

The research team analysed feathers from Aquatic Warblers caught in Europe to help narrow their search. Knowing that the feathers would have been grown on African wintering grounds, the researchers looked for patterns of isotopes and compared these alongside isotope maps of West Africa.

The study revealed that the birds spend the winter at sites in a zone just south of the Sahara. An analysis of the few African records in combination with a computer modelling of potentially suitable climatic conditions led researchers to likely areas bordering the Senegal river.

"It's a long-awaited discovery that gives encouragement to conservationists in both Europe and Africa," commented Paul K Ndanganga, BirdLife's African Species Working Group Co-ordinator. "As we increase our knowledge of the areas that are important for warblers, conservationists in the region can now focus efforts into site monitoring, the next step in helping ensure these wintering grounds are adequately managed and better protected."

Lachmann added: "Thankfully, substantial parts of the bird's wintering range fall within protected areas, with the Djoudj National Park alone possibly holding up to a third of the world population. This wetland, on the southern edge of the Sahara, is likely to be threatened by the southward advance of the Sahara fuelled by climate change. This encroachment is likely to limit the water supply for the national park."

Aquatic Warbler has declined dramatically in Europe over the last century, and its global population is now down to 15,000 pairs - largely because of drainage of its wetland nesting sites. An estimated 95% of habitat has been lost in the last century.

Future work in the field and with satellite maps will help identify other potential sites in southern Mauritania and elsewhere in western Africa.