Spatial and Temporal Variability in Migration of a Soaring Raptor Across Three Continents

Disentangling individual- and population-level variation in migratory movements is necessary for understanding migration at the species level. However, very few studies have analyzed these patterns across large portions of species' distributions. We compiled a large telemetry dataset on the globally endangered Egyptian Vulture Neophron percnopterus (94 individuals, 188 completed migratory journeys), tracked across ~70% of the species' global range, to analyze spatial and temporal variability of migratory movements within and among individuals and populations. We found high migratory connectivity at large spatial scales (i.e., different subpopulations showed little overlap in wintering areas), but very diffuse migratory connectivity within subpopulations, with wintering ranges up to 4,000 km apart for birds breeding in the same region and each subpopulation visiting up to 28 countries (44 in total). Additionally, Egyptian Vultures exhibited a high level of variability at the subpopulation level and flexibility at the individual level in basic migration parameters. Subpopulations differed significantly in travel distance and straightness of migratory movements, while differences in migration speed and duration differed as much between seasons and among individuals within subpopulations as between subpopulations. The total distances of the migrations completed by individuals from the Balkans and Caucasus were up to twice as long and less direct than those in Western Europe, and consequently were longer in duration, despite faster migration speeds. These differences appear to be largely attributable to more numerous and wider geographic barriers (water bodies) along the eastern flyway. We also found that adult spring migrations to Western Europe and the Balkans were longer and slower than fall migrations. We encourage further research to assess the underlying mechanisms for these differences and the extent to which environmental change could affect Egyptian Vulture movement ecology and population trends.

Balkans and Caucasus data: This work was financially supported by the LIFE+ projects LIFE10 NAT/BG/000152 and LIFE 16 NAT/BG/000874 funded by the European Union and co-funded by the AG Leventis Foundation and MAVA, the US National Science Foundation, the Christensen Fund, National Geographic Society, the Whitley Fund for Nature, Faruk Yalçin Zoo and Kuzey Doga's donors (in particular Bilge Bahar, Devrim Celal, Seha Işmen, Lin Lougheed, Burak Över, and Batubay Özkan). We are grateful to Turkey's Ministry of Forestry and Water Affairs General Directorate of Nature Conservation and National Parks and NorthStar Science and Technology for donating three transmitters each. State Nature Reserve Dagestanskiy and Russian Raptor Research and Conservation Network supported work in Dagestan. Western Europe data: deployments of transmitters in Portugal were funded by the EU-funded LIFE Rupis project (LIFE14 NAT/PT/00855); SALORO S.L.U. funded the deployment of transmitters in the Duero region of Spain; DREAL Nouvelle-Aquitaine—Fondation d'entreprises Barjane funded deployments in France; JE was supported by Basque government predoctoral grant (grant number: 569382696); GREFA (Grupo para la Rehabilitación de la Fauna Autóctona y su habitat)-Endangered Species Monitoring Project together with Poison Sentinels Project of WWF/Spain. The Migra Program of SEO/BirdLife (www.migraciondeaves.org/en/) deployed transmitters in collaboration with Fundación Iberdrola España, and were funded by La Rioja Regional Government in La Rioja, and Fundación Hazi and Diputación Foral de Gipuzkoa within the Interreg POCTEFA-ECOGYP project in Gipuzkoa.