Highly pathogenic avian influenza causes mass mortality in Sandwich Tern Thalasseus sandvicensis breeding colonies across north-western Europe

Ulrich Knief*, Thomas Bregnballe, Ibrahim Alfarwi, Mónika Z. Ballmann, Allix Brenninkmeijer, Szymon Bzoma, Antoine Chabrolle, Jannis Dimmlich, Elias Engel, Ruben Fijn, Kim Fischer, Bernd Hälterlein, Matthias Haupt, Veit Hennig, Christof Herrmann, Ronald In 'T Veld, Elisabeth Kirchhoff, Mikael Kristersson, Susanne Kühn, Kjell LarssonRolf Larsson, Neil Lawton, Mardik Leopold, Sander Lilipaly, Leigh Lock, Régis Marty, Hans Matheve, Włodzimierz Meissner, Paul Morrison, Stephen Newton, Patrik Olofsson, Florian Packmor, Kjeld T. Pedersen, Chris Redfern, Francesco Scarton, Fred Schenk, Olivier Scher, Lorenzo Serra, Alexandre Sibille, Julian Smith, Wez Smith, Jacob Sterup, Eric Stienen, Viola Strassner, Roberto G. Valle, Rob S.A. van Bemmelen, Jan Veen, Muriel Vervaeke, Ewan Weston, Monika Wojcieszek, Wouter Courtens

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

1 Citation (Scopus)


In 2022, highly pathogenic avian influenza (HPAI) A(H5N1) virus clade became enzootic and caused mass mortality in Sandwich Tern Thalasseus sandvicensis and other seabird species across north-western Europe. We present data on the characteristics of the spread of the virus between and within breeding colonies and the number of dead adult Sandwich Terns recorded at breeding sites throughout north-western Europe. Within two months of the first reported mortalities, 20,531 adult Sandwich Terns were found dead, which is >17% of the total north-western European breeding population. This is probably an under-representation of total mortality, as many carcasses are likely to have gone unnoticed and unreported. Within affected colonies, almost all chicks died. After the peak of the outbreak, in a colony established by late breeders, 25.7% of tested adults showed immunity to HPAI subtype H5. Removal of carcasses was associated with lower levels of mortality at affected colonies. More research on the sources and modes of transmission, incubation times, effective containment, and immunity is urgently needed to combat this major threat for colonial seabirds.

Original languageEnglish
Article numbere6
JournalBird Conservation International
Publication statusPublished - 2 Feb 2024


  • Avian flu
  • H5N1
  • Highly pathogenic avian influenza virus
  • HPAI
  • Seabird conservation
  • Sero-surveillance
  • Wildlife disease management


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