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Published April 24, 2026 | Version v1
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Supplementary material for: Niederberger "Spatial variation in differential migration affects the range-wide migratory network in an endemic European raptor species"

Authors/Creators

  • 1. Swiss Ornithological Institute, Sempach, Switzerland
  • 2. Department of Geography, University of Zurich, Zurich, Switzerland
  • 3. Scientific Computing Center, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 4. Conservatoire d'espaces naturels de Corse (CEN Corse), Borgo, France
  • 5. BirdWings, El Escorial, Madrid, Spain
  • 6. Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands
  • 7. Plaza de la Provincia, Vitoria-Gasteiz (Älava/Araba), Spain
  • 8. CERM Endangered Raptors Centre Association, Rocchette di Fazio (GR), Italy
  • 9. LPO France, Parc Montsouris, Paris, France
  • 10. Milan royal Pyrénées LPO Délégation territoriale Aquitaine, Campan, France
  • 11. Grupo de Ecología Terrestre (TEG-UAM), Departamento de Ecología, Centro de Investigación en Biodiversidad y Cambio Global (CIBC-UAM), Universidad Autónoma de Madrid, Madrid, Spain
  • 12. Philipps-Universität Marburg, Conservation Ecology, Marburg, Germany
  • 13. AMUS (Acción por el Mundo Salvaje), Villafranca De Los Barros, Spain
  • 14. Rotmilanzentrum am Museum Heineanum, Halberstadt, Germany
  • 15. Department of Biology and Wildlife Diseases, Faculty of Veterinary Hygiene and Ecology, University of Veterinary Sciences Brno, Brno, Czech Republic
  • 16. Department of Game Management and Forest Protection, Poznań University of Life Sciences, Poznań, Poland
  • 17. RSPB Scotland, Edinburgh, Scotland
  • 18. C/ Manuel Sanchis Guarner 10, Palma, Mallorca, Spain
  • 19. TB Raab GmbH, Deutsch-Wagram, Austria
  • 20. ANITRA System s.r.o., Praha 10 Vršovice, Czech Republic
  • 21. Northern Ireland Raptor Study Group (NIRSG) Castle Archdale Country Park, Irvinestown Fermanagh, Northern Ireland
  • 22. Golden Eagle Trust, Airfield Park, Donnybrook, Dublin, Ireland
  • 23. Deltamilieu Projecten, Vlissingen, the Netherlands

Description

Abstract

Migratory connectivity, the linkage between breeding and non-breeding populations, is crucial for understanding the ecology and conservation of migratory species across their range. Differential migration, where subgroups within a population have varying migratory strategies (e.g. different migration flyways), is common in many vertebrate species and predicted to affect migratory connectivity. However, empirical evidence for this prediction is largely lacking due to logistical and financial constraints.

Here, we examine the impact of differential migration on the range-wide migratory network and migratory connectivity of the red kite (Milvus milvus) using an unprecedented GPS tracking dataset of 2,440 annual cycles from 1,020 individuals, along with range-wide breeding abundance maps.

Our analysis reveals significant spatial variation in age-dependent residency and flyways, creating a mosaic of differential migration across the species’ range. Unlike adults and immature birds, juveniles show more spatial variation in migration strategy, with 21.3% of the global juvenile population and 43.6% of the adults remaining resident year-round. We identified a clear migratory divide, with 77.7% of all juveniles and 54.0% of adults adopting a western flyway, and 68% of the global juvenile and 56% of the adult population overwintering on the Iberian Peninsula. Combining transition probabilities with abundance estimates indicated weak, but age-structured migratory connectivity, with migratory connectivity (MC) values decreasing from 0.34 in juveniles to 0.27 in adults. As higher values indicate greater separation and less mixing on the wintering grounds, our results suggest that adults from different breeding populations mix more extensively than juveniles, highlighting an age-related diversification of migration patterns.

These findings highlight the need for tailored management strategies that account for age-specific migration patterns and their geographic variation. Our study provides the first empirical evidence that age-structured differential migration causes age-specific migratory connectivity across a vertebrate’s entire range, with important implications for conservation and population management.

 

Files

Codes_Data_Niederberger_MigConnectivity_RedKite.zip

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