Importance of African Convergence Sites for Migratory Birds After Crossing the Sahara

We ask why migrating birds stop where they do, and what a stopover achieves for the individual. We study the energetic, nutritional and temporal costs and benefits of stopping in the savannahs south of the Sahel, and link them to seasonal habitat conditions. Existing data show the advantages of African sites for nonbreeding birds, but also the risks associated with degradation due to land use changes. Whereas our sister project Hotspots asks which sites along the flyway matter, here we focus on what happens to birds at these sites.

Studies have initially concentrated on a few intensively studied stopover sites in South Sudan, together with partners at the University of Juba, but the project is now expanding to other parts of Africa. It explores the energetic and trophic aspects of European-breeding birds’ diet at these sites where multiple species overlap. Stable isotope and metabarcoding techniques assess these associations at different scales. We use non-invasive techniques, including sampling of feathers, breath, faeces and blood, to gather data on ecology and body condition at individual, population and species levels.
The design overall favours depth over broad coverage.

Bird migration is a challenging journey, especially after crossing the desert. At convergence sites, many European songbird species break from migration to rest and refuel. Of these species, 30-40% undergo complete moult at African stopovers. The quality and extent of moult and the ability to continue migration depend on resource availability at stopovers. Birds leaving in poor condition carry that deficit through the rest of the annual cycle. Our project provides mechanistic evidence for what a bird gains, or fails to gain, during a stay. This information is important to prioritise sites and advocate for their protection.
The protection of these sites is essential to ensuring successful migration and maintaining healthy populations.

Assigning origins from feather isoscapes is often difficult for long-distance migrants, because validated data are scarce. We use stable isotope data [add link to upcoming expertise page on isotopes] from contemporary and archived feathers of both migratory and resident birds to create an isoscape for the Sahel savannah region. We identify the vegetation, altitude and rainfall variables that shape it. Our aim is to enhance precipitation isoscape models and refine the feather-based isoscapes. The framework is also used by our sister project Hotspots to assign moulting origins across the flyway.

• University of Juba, South Sudan
• Ministry of Environment, South Sudan
• Museum of Nairobi, Kenya