Toward a Deuterium Feather Isoscape for Sub-Saharan Africa: Progress, Challenges and the Path Ahead

A key challenge to the application of continent-wide feather isoscapes for geographic assignment of migrant birds is the lack of ground-truthed samples. This is especially true for long-distance Palearctic-Afrotropical migrants. We used spatially-explicit information on the δ (2)H composition of archived feathers from Green-backed/Grey-backed Camaroptera, to create a feather δ (2)H isoscape for sub-Saharan Africa. We sampled from 34 out of 41 sub-Saharan countries, totaling 205 sampling localities. Feather samples were obtained from museum collections (n = 224, from 1950 to 2014) for δ (2)H assay. Region, altitude, annual rainfall and seasonal patterns in precipitation were revealed as relevant explanatory variables for spatial patterns in feather δ (2)H. Predicted feather δ (2)H values ranged from -4.0 ‰ to -63.3 ‰, with higher values observed in the Great Rift Valley and South Africa, and lower values in central Africa. Our feather isoscape differed from that modelled previously using a precipitation δ (2)H isoscape and an assumed feather-to-precipitation calibration, but the relatively low model goodness fit (F(10,213) = 5.98, p<0.001, R(2) = 0.18) suggests that other, non-controlled variables might be driving observed geographic patterns in feather δ (2)H values. Additional ground-truthing studies are therefore recommended to improve the accuracy of the African feather δ (2)H isoscape.