Stephen Baillie

Honorary Research Fellow

To undertake, develop and supervise research on processes determining avian distributions and abundances, from local to continental scales, primarily using high quality citizen science data collected by the BTO and similar organizations. Stephen has particular interests in population dynamics and in studies of year-round abundance, migration routes and phenology.

Interests & Responsibilities

Patterns of avian abundance arise from variation in reproductive rates and survival, and at smaller scales also from dispersal. Stephen has had a long term involvement in the development of BTO’s Integrated Population Monitoring Programme, where it uses its volunteer-based demographic monitoring schemes to provide measures of breeding success and survival for a wide range of species (for current trends see

Stephen's current work focuses on the use of Integrated Population Models to understand these demographic processes within a coherent statistical framework. He is interested in the ways in which environmental conditions and competitive interactions (density-dependence) interact to determine large-scale abundance patterns.

The second major research interest is the use of Citizen Science data to study year-round patterns of occurrence, abundance, migration and phenology at national and continental scales. This research involves leading analyses of Birdtrack data and collaboration with European colleagues to develop a continental approach through the EuroBirdPortal project, which is bringing together similar datasets from across Europe. Stephen leads BTO’s input to EuroBirdPortal which will soon deliver close to real-time continental-scale outputs.

In a related initiative, he is working with colleagues in EURING to develop a European Migration Atlas based on ring recoveries and tracking data. This will be based on data from the EURING databank which is hosted by BTO. Tracking technologies are rapidly advancing our knowledge of avian movement patterns.

Stephen is collaborating with BTO volunteer, Graham Geen, on an extensive review of tracking studies to evaluate their potential impacts on birds and as an input to the European Migration Atlas.

Large-scale studies of avian ecology offer opportunities for substantial advances in our understanding of year-round patterns of avian occurrence and abundance and of the demographic processes that underpin them. Such knowledge is essential for increasing our understanding of the impacts of environmental and climate change, and how these can best be managed. 

Other Information

  • Honorary Reader in Biological Sciences, University of East Anglia
  • Chair of European Union for Bird Ringing (EURING) Atlas Committee
  • Member of EuroBirdPortal steering group
  • Researcher at BTO since 1980
  • Former BTO Director of Science (1987-2014), during which time he led the establishment of the Breeding Bird Survey and BirdTrack, the scientific development of demographic monitoring (Ringing, Nest Records, Constant Effort Sites, Retrapping Adults for Survival) and the BTO’s use of the internet to gather scientific data and disseminate the results.
  • Current research student: Marina Jiminez-Munoz, School of Mathematics, Statistics and Actuarial Science, University of Kent. Co-supervised with Drs Diana Cole, Eleni Matechou and Rob Robinson, Research project on spatially explicit integrated population models.


  • BSc (Hons) Zoology, University of Aberdeen, 1972-76
  • PhD, Population dynamics of the Eider (Somateria mollissima) in North-East Scotland, University of Aberdeen, 1976-1980

Recent BTO Publications

Border, J.A., Boersch-Supan, P., Pearce-Higgins, J.W., Hewson, C., Howard, C., Stephens, P.A., Willis, S.G., Houston, A., Gargallo, G. & Baillie, S.R. 2024. Spatial variation in spring arrival patterns of Afro-Palearctic bird migration across Europe. Global Ecology and Biogeography View at journal website (DOI: 10.1111/geb.13850)
Fattorini, N., Costanzo, A., Romano, A., Rubolini, D., Baillie, S., Bairlein, F., Spina, F., & Ambrosini, R. 2023. Eco-evolutionary drivers of avian migratory connectivity. Ecology Letters View at journal website (DOI: 10.1111/ele.14223)
Massimino, D., Woodward, I.D., Barber, L., Barimore, C., Harris, S.J., Leech, D.I., Noble, D.G., Walker, R.H., Baillie, S.R. & Robinson, R.A. 2023. BirdTrends 2022. British Trust for Ornithology, Thetford, Norfolk Link to publication
Gargallo, G., Davies, J.G., Faverjon, C., Kampichler, C., Baillie, S.R., Cameron, A., Robinson, R.A. & Sierdsema H. 2022. Development of a prototype early warning system for avian influenza in the EU based on risk-mapping. EFSA Supporting Publications 19 (part 12) European Food Safety Agency View at journal website (DOI: 10.2903/sp.efsa.2022.EN-7762)
Caliendo. V., Lewis, N.S., Pohlmann, A., Baillie, S.R., Banyard, A.C., Beer, M., Brown, I.H., Fouchier, R.A.M., Hansen, R.D.E., Lameris, T.K., Lang, A.S., Laurendaeu, S., Lung, O., Robertson, G., van der Jeugd, H., Alkie, T.N., Thorup, K., van Toor, M.L., Waldenstrom, J., Yason, C., Kuiken, T. & Berhane, Y. 2022. Transatlantic spread of highly pathogenic avian influenza H5N1 by wild birds from Europe to North America in 2021. Scientific Reports 12 Link to publication View at journal website (DOI: /10.1038/s41598-022-13447-z)
Woodward, I.D., Massimino, D., Hammond, M.J., Barber, L., Barimore, C., Harris, S.J., Leech, D.I., Noble, D.G., Walker, R.H., Baillie, S.R. & Robinson, R.A. 2021. BirdTrends 2020. British Trust for Ornithology, Thetford, Norfolk Link to publication

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