Avian influenza causes age-related mortality in a long-lived seabird

Courtens, W.; Ballmann, M. Z.; Fijn, R. C.; Frederiksen, M.; Kuehn, S.; Lens, L.; Leopold, M. F.; Lilipaly, S.; Packmor, F.; Stienen, E. W. M.; van Horssen, P.; Knief, U.

doi:10.1101/2025.10.30.685500

bioRxiv · 10.1101/2025.10.30.685500

Avian influenza causes age-related mortality in a long-lived seabird

Courtens, W.·Ballmann, M. Z.·Fijn, R. C.·Frederiksen, M.·Kuehn, S.·Lens, L.·Leopold, M. F.·Lilipaly, S.·Packmor, F.·Stienen, E. W. M.·van Horssen, P.·Knief, U.

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Abstract

Recently, highly pathogenic avian influenza (HPAI) A (H5N1) clade 2.3.4.4b viruses have caused mass mortality events in seabirds worldwide, raising concern for long-lived species with low reproductive rates. Using individual-level data from the 2022 mass mortality event in northwestern European Sandwich terns (Thalasseus sandvicensis), we show that older individuals were disproportionately more affected, while no sex bias was observed. This age-specific mortality likely removed the most experienced individuals from the population. Our findings highlight a previously underappreciated mechanism through which HPAI outbreaks may impair the resilience of long-lived avian populations.

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Courtens, W., Ballmann, M. Z., Fijn, R. C., Frederiksen, M., Kuehn, S., Lens, L., Leopold, M. F., Lilipaly, S., Packmor, F., Stienen, E. W. M., van Horssen, P., Knief, U.. 2025-10-31. Avian influenza causes age-related mortality in a long-lived seabird. https://doi.org/10.1101/2025.10.30.685500

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