Biodiversity and Conservation

, Volume 25, Issue 2, pp 295–309 | Cite as

Trends of autumn counts at Iberian migration bottlenecks as a tool for monitoring continental populations of soaring birds in Europe

  • Beatriz Martín
  • Alejandro Onrubia
  • Andrés de la Cruz
  • Miguel Ferrer
Original Paper


Migration monitoring may allow us to detect population trends over large geographic areas because the pattern of change in migrant counts may be expected to follow the pattern of change in population size. We analysed recent regional European population trends of migratory soaring birds from rates of change in migration counts over the Strait of Gibraltar (Spain) during the years (1999–2013). An additional bottleneck (Organbidexka, France) within the same migratory route and period was also considered. We estimated count trends by fitting a log-generalized linear model to the time series of each species counts. The counts in Organbidexka were used to test the consistency in the observed trends over the Strait of Gibraltar. Migration counts of White and Black Storks, Black Kites, Short-toed and Booted Eagles as well as Egyptian Vultures showed a linear increase over the Strait of Gibraltar throughout the 15-year period. In contrast, Honey Buzzard numbers remained stable. Trends were highly consistent with those recorded in Organbidexka. We suggest that the larger slopes for the trends in Organbidexka when compared with the Strait reflect an increasing tendency in these species to overwinter in southern Europe. A combination of complementary data sets collected at different bottleneck sites within the European–African flyway system may become a fundamental tool for the investigation of migratory patterns and population trends and changes of soaring migrant birds all over Europe.


Bottleneck Global change Organbidexka Raptors Storks Strait of Gibraltar 



We are grateful to the thousands of people (volunteers and staff) who collected the information presented in this study and to the Board of the Migres Foundation. The data counts from the Strait of Gibraltar analyzed in the study were collected in field monitoring campaigns 1999/2012 funded by grants of the Consejeria de Medio Ambiente of the Junta de Andalucía (Spain). We would like to thank Andrew Paterson for his revision of the language of the manuscript. We would also like to thank the editor and two anonymous referees for providing us with comments and suggestions which helped to improve the manuscript.


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Copyright information

© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  • Beatriz Martín
    • 1
  • Alejandro Onrubia
    • 1
  • Andrés de la Cruz
    • 1
  • Miguel Ferrer
    • 2
  1. 1.Fundación MigresCádizSpain
  2. 2.Applied Ecology GroupDoñana Biological Station, CSICSevilleSpain

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