Skip to main content

Towards a cumulative collision risk assessment of local and migrating birds in North Sea offshore wind farms


Bird collision assessments are generally made at the scale of a single wind farm. While especially in offshore situations such assessments already hold several assumptions, even bigger challenges exist on estimating the cumulative impact of multiple wind farms and the impacts at population level. In this paper, the number of collision victims at Belgian offshore wind farms was estimated with a (theoretical) collision risk model based on technical turbine specifications, bird-related parameters and bird density data of both local seabirds and passerine migrants. Bird density data were gathered by visual censuses and radar registrations. The outcome of the model was extrapolated to future development scenarios in the Belgian part of the North Sea and in the entire North Sea, and then further used for a preliminary assessment of the impact at population level for the species at risk. The results indicate that the cumulative impact of a realistic scenario of 10,000 turbines in the North Sea might have a significant negative effect at population level for lesser and great black-backed gull. We further show that during a single night of intense songbird migration, the number of collision victims among passerine migrants might be in the order of magnitude of several thousands in the entire North Sea. We argue that it is of great importance to further develop methods to quantify the uncertainties and to minimise the assumptions, in order to assure more reliable cumulative impact assessments.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2


  • Alerstam, T., 1990. Bird Migration. Cambridge University Press, Cambridge: 420pp.

  • Alerstam, T., M. Rosén, J. Bäckman, P. G. P. Ericson & O. Hellgren, 2007. Flight speeds among bird species: allometric and phylogenetic effects. PLoS Biology 5(8): e197.

    PubMed Central  PubMed  Article  Google Scholar 

  • Band, B., 2012. Using a collision risk model to assess bird collision risks for offshore wind farms. British Trust for Ornithology.

  • Barclay, R. M. R., E. F. Baerwald & J. C. Gruver, 2007. Variation in bat and bird fatalities at wind energy facilities: assessing the effects of rotor size and tower height. Canadian Journal of Zoology 85: 381–387.

    Article  Google Scholar 

  • BirdLife International, 2004. Birds in Europe: Population estimates, trends and conservation status. BirdLife International, Cambridge.

    Google Scholar 

  • Bourne, W. P. R., 1980. The midnight descend, dawn ascent and reorientation of landbirds migrating across the North Sea in autumn. Ibis 122: 536–540.

    Article  Google Scholar 

  • BTO, 2013. Bird Facts. Available at

  • Buurma, L. S., 1987. Patronen van hoge vogeltrek boven het Noordzeegebied in oktober. Limosa 60: 63–74.

    Google Scholar 

  • Chamberlain, D. E., M. R. Rehfisch, A. D. Fox, M. Desholm & S. J. Anthony, 2006. The effect of avoidance rates on bird mortality predictions made by wind turbine collision risk models. Ibis 148: 198–202.

    Article  Google Scholar 

  • Collier, M. P., S. Dirksen & K. L. Krijgsveld, 2012. A review of methods to monitor collisions or micro-avoidance of birds with offshore wind turbines: Part 2: Feasibility study of systems to monitor collisions. Strategic Ornithological Support Services Project SOSS-03A.

  • Cook, A. S. C. P., L. J. Wright & N. H. K. Burton, 2012. A review of flight heights and avoidance rates in relation to offshore wind farms. Strategic Ornithological Support Services Project SOSS-02. BTO Research Report 618. BTO, Thetford.

  • Cramp, S. (ed), 1977–1985. The birds of the Western Palearctic. Handbook of the birds of Europe, the Middle East and North Africa, Vol. 1, 3 & 4. Oxford University Press, Oxford.

  • Croxall, J. P. & P. Rothery, 1991. Population regulation of seabirds: implications of their demography for conservation. In Perrins, C. M., J.-D. Lebreton & G. J. M. Hirons (eds), Bird Population Studies: Relevance to conservation and management. Oxford University Press, New York: 272–296.

    Google Scholar 

  • Dierschke, V., O. Hüppop & S. Garthe, 2003. Populationsbiologische Schwellen der Unzulässigkeit für Beeinträchtigungen der Meeresumwelt am Beispiel der in der deutschen Nord- und Ostsee vorkommenden Vogelarten. Seevogel 24: 61–72.

    Google Scholar 

  • Drewitt, A. L. & R. H. W. Langston, 2006. Assessing the impact of wind farms on birds. Ibis 148: 29–42.

    Article  Google Scholar 

  • Everaert, J., 2013, in preparation. Aanvullingen op het rapport “Risico’s voor vogels en vleermuizen bij geplande windturbines in Vlaanderen”. Aanzet voor beoordelings- en significatiekader. Research Institute for Nature and Forest, Brussels.

  • Everaert, J. & E. W. M. Stienen, 2007. Impact of wind turbines on birds in Zeebrugge (Belgium). Significant effect on breeding tern colony due to collisions. Biodiversity and Conservation 16: 3345–3359.

    Article  Google Scholar 

  • Everaert, J., 2014. Collision risk and micro-avoidance rates of birds with wind turbines in Flanders. Bird Study 61: 220–230.

    Article  Google Scholar 

  • EWEA, 2011. European Offshore Wind 2011 Map. Available at

  • EWEA, 2014. The European offshore wind industry – key trends and statistics 2013. Available at

  • Fox, A. D., M. Desholm, J. Kahlert, T. K. Christensen & I. K. Petersen, 2006. Information needs to support environmental impact assessment of the effects of European marine offshore wind farms on birds. Ibis 148: 129–144.

    Article  Google Scholar 

  • Frederiksen, M., S. Wanless, M. P. Harris, P. Rothery & L. J. Wilson, 2004. The role of industrial fisheries and oceanographic change in the decline of North Sea black legged kittiwakes. Journal of Applied Ecology 41: 1129–1139.

    Article  Google Scholar 

  • Furness, R. W., H. M. Wade & E. A. Masden, 2013. Assessing vulnerability of marine bird populations to offshore wind farms. Journal of Environmental Management 119: 56–66.

    PubMed  Article  Google Scholar 

  • Garthe, S. & O. Hüppop, 2004. Scaling possible adverse effects of marine wind farms on seabirds: developing and applying a vulnerability index. Journal of Applied Ecology 41: 724–734.

    Article  Google Scholar 

  • Hartman, J. C., K. L. Krijgsveld, M. J. M. Poot, R. C. Fijn, M. F. Leopold & S. Dirksen, 2012. Effects on birds of offshore wind farm Egmond aan Zee (OWEZ) an overview and integration of insights obtained. Bureau Waardenburg, Culemborg.

    Google Scholar 

  • Hüppop, O., J. Dierschke, K.-M. Exo, E. Fredrich & R. Hill, 2006. Bird migration studies and potential collision risk with offshore wind turbines. Ibis 148: 90–109.

    Article  Google Scholar 

  • Johnston, A., A. S. C. P. Cook, L. J. Wright, E. M. Humphreys & N. H. K. Burton, 2014. Modelling flight heights of marine birds to more accurately assess collision risk with offshore wind turbines. Journal of Applied Ecology 51: 31–41.

  • Krijgsveld, K. L., R. C. Fijn, M. Japink, P. W. van Horssen, C. Heunks, M. P. Collier, M. J. M. Poot, D. Beuker & S. Dirksen, 2011. Effect studies offshore wind farm Egmond aan Zee—final report on fluxes, flight altitudes and behaviour of flying birds. Bureau Waardenburg, Culemborg.

    Google Scholar 

  • Lack, D., 1963. Migration across the southern North Sea studied by radar. Part 4. Autumn. Ibis 105(1): 1–54.

    Article  Google Scholar 

  • Langston, R. H. W. & J. D. Pullan, 2003. Windfarms and Birds: an analysis of the effects of windfarms on birds, and guidance on environmental assessment criteria and site selection issues. Report T-PVS/Inf (2003) 12. Birdlife International.

  • Lensink, R., H. van Gasteren, F. Hustings, L. S. Buurma, G. van Duin, L. Linnartz, F. Vogelzang & C. Witkamp, 2002. Vogeltrek over Nederland 1976–1993. Schuyt & Co, Haarlem.

    Google Scholar 

  • Masden, E. A., A. D. Fox, R. W. Furness, R. Bullman & D. T. Haydon, 2010. Cumulative impact assessments and bird/wind farm interactions: developing a conceptual framework. Environmental Impact Assessment Review 30: 1–7.

    Article  Google Scholar 

  • Mitchell, P. I., S. F. Newton, N. Ratcliffe & T. E. Dunn, 2004. Seabird populations of Britain and Ireland. Results of the seabird 2000 census (1998–2002). T & A D Poyser, London.

    Google Scholar 

  • OSPAR, 2009. Background Document for Black-legged kittiwakes Rissa tridactyla OSPAR commission. London: 27pp.

  • Pennycuick, C. J., 1997. Actual and ‘optimum’ flight speeds: field data reassessed. Journal of Experimental Biology 200: 2355–2361.

    PubMed  Google Scholar 

  • Poot, M., P. W. van Horssen, M. Collier, R. Lensink & S. Dirksen, 2011. Effect studies offshore wind Egmond aan Zee: cumulative effects on seabirds – a modelling approach to estimate effects on population levels in seabirds. Bureau Waardenburg, Culemborg.

    Google Scholar 

  • Sæther, B. E. & Ø. Bakke, 2000. Avian life history variation and contribution of demographic traits to the population growth rate. Ecology 81: 642–653.

    Article  Google Scholar 

  • Seys, J., 2002. Estimates of the number of seabirds residing in and migrating through the southern North-Sea. Report IN.D.2002.2. Institute of Nature Conservation, Brussels.

  • Stienen, E. W. M., J. Van Waeyenberge, E. Kuijken & J. Seys, 2007. Trapped within the corridor of the Southern North Sea: the potential impact of offshore wind farms on seabirds. In de Lucas, M., G. F. E. Janss & M. Ferrer (eds), Birds and wind farms – risk assessment and mitigation. Quercus, Madrid: 71–80.

    Google Scholar 

  • Stone, C. J., A. Webb, C. Barton, N. Ratcliffe, T. C. Reed, M. L. Tasker, C. J. Camphuysen & M. W. Pienkowski, 1995. An atlas of seabird distribution in north-west European waters. Joint Nature Conservation Committee, Peterborough.

    Google Scholar 

  • Tasker, M. L., P. H. Jones, T. J. Dixon & B. F. Blake, 1984. Counting seabirds at sea from ships: a review of methods employed and a suggestion for a standardised approach. Auk 101: 567–577.

    Google Scholar 

  • Tasker, M. L., A. Webb, A. J. Hall, M. P. Pienkowski & D. R. Langslow, 1987. Seabirds in the North Sea. Nature Conservancy Council, Aberdeen.

    Google Scholar 

  • Vanermen N., R. Brabant, E. W. M. Stienen, W. Courtens, T. Onkelinx, M. Van de walle, H. Verstraete, L. Vigin & S. Degraer, 2013. Bird monitoring at the Belgian offshore wind farms: results after five years of impact assessment. In Degraer, S., R. Brabant & B. Rumes (eds), 2013. Environmental impacts of offshore wind farms in the Belgian part of the North Sea: Learning from the past to optimise future monitoring programmes. Royal Belgian Institute of Natural Sciences, Operational Directorate Natural Environment, Marine Ecology and Management Section: 49–61.

  • Vanermen, N., T. Onkelinx, W. Courtens, M. Van de Walle, H. Verstraete & E. W. M. Stienen, 2014. Seabird avoidance and attraction at an offshore wind farm in the Belgian part of the North Sea. Hydrobiologia. doi:10.1007/s10750-014-2088-x.

    Google Scholar 

  • Venables, W. N. & B. D. Ripley, 2002. Modern applied statistics with S, 4th ed. Springer, New York.

    Book  Google Scholar 

  • Wetlands International, 2013. Waterbird Population Estimates. Available at:

  • WWT Consulting, 2012. Demographic data, population model and outputs. SOSS-04 Gannet Population Viability Analysis:61pp.

Download references


The authors acknowledge C-Power and Belwind for their willing cooperation throughout the research. The crew of the RV Belgica, RV Zeeleeuw and RV Simon Stevin are thanked for their enthusiasm and technical support throughout the sampling campaigns. Lieven Naudts from the Royal Belgian Institute of Natural Sciences (RBINS) and André Cattrijsse & Michiel Tjampens from the Flanders Marine Institute (VLIZ) are especially thanked for their invaluable logistic support. Ship time on RV Belgica was provided by the Belgian Science Policy (BELSPO) and Royal Belgian Institute of Natural Sciences, Operational Directorate Natural Environment. Ship time on the RV Zeeleeuw and RV Simon Stevin was provided by DAB Vloot and the Flanders Marine Institute (VLIZ).

Finally, we wish to thank all colleagues and volunteers who assisted in the seabird counts, especially to Wouter Courtens, Hilbran Verstraete, Marc Van de walle & Walter Wackenier.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Robin Brabant.

Additional information

R. Brabant and N. Vanermen shared first authorship

Guest editors: Steven Degraer, Jennifer Dannheim, Andrew B. Gill, Han Lindeboom & Dan Wilhelmsson/Environmental impacts of offshore wind farms

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Brabant, R., Vanermen, N., Stienen, E.W.M. et al. Towards a cumulative collision risk assessment of local and migrating birds in North Sea offshore wind farms. Hydrobiologia 756, 63–74 (2015).

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:


  • Offshore wind farms
  • Bird collisions
  • Seabirds
  • Bird migration
  • Collision risk modelling
  • Impact assessment