Feather isotope tells where migrants come from in Africa
Research Background
The survival of migratory passerines depends considerably on conditions experienced on their non-breeding grounds. However, these critical non-breeding sites are generally poorly known, especially for species and populations using the eastern Afro-Palearctic flyway. To fill this gap, we measured hydrogen stable isotopes in winter-grown feathers (δ2Hf) of five long-distance migratory passerines (Eurasian Blackcap, Eastern Olivaceous Warbler, Eurasian Reed Warbler, Olive-tree Warbler, and Barred Warbler) collected during spring migration at a stopover site in Israel, a major migratory bottleneck in the Afro-Palearctic Flyway.
Research Objectives
We determined non-breeding origins of these species, for the entire migrating population and for early- and late-arriving individuals separately. We used a probabilistic model based on feather isotopes and isotopic distribution of precipitation δ2H (δ2Hp) in Africa, as well as range maps derived from species distribution models and expert opinion.
Results
Assignments to African non-breeding grounds of the study species, based on feather hydrogen (δ2Hf) of birds flying through Jerusalem, Israel. Feather isotopic values were probabilistically assigned to a derived δ2Hf ‘isoscape’ based on a precipitation δ2H surface. Isotopic assignment was conducted within SDM-based maps (a–e) and published expert-drawn maps (f–j). Legend indicates the proportion of individuals that potentially spent their non-breeding seasons at a particular location in the likelihood surface, where darker colors represent higher probability. The number of individuals included in the analysis is indicated for each species at the bottom of its column. For example, 149 individual Blackcaps feathers were collected and analyzed, from which, 80% (~ 119 individuals) are likely originated in the areas indicated by the nearly darkest color, according to the isotopic-assignment analysis.
While our results suggested that Reed Warbler and Olive-tree Warbler occupy most of their known range during the non-breeding season, Blackcaps migrating through Jerusalem, Israel, likely spent the non-breeding season specifically in Ethiopia and near areas, and Eastern Olivaceous Warbler concentrated in two regions in eastern tropical and central Africa. Barred Warblers’ non-breeding grounds were estimated in Kenya, but the species distribution model approach suggested additional regions. Our results further suggested that early- and late-arriving Reed Warblers spent the non-breeding season in separate areas, whereas early- and late-arriving Blackcaps migrated to the same area.
