High pathogenicity avian influenza (H5N1) in Northern Gannets: Global spread, clinical signs, and demographic consequences
Authors: Lane Jude V , Jeglinski Jana WE , Avery-Gomm Stephanie , Ballstaedt Elmar , Banyard Ashley C , Barychka Tatsiana , Brown Ian H , Brugger Brigitte , Burt Tori V , Careen Noah , Castenschiold Johan HF , Christensen-Dalsgaard Signe , Clifford Shannon , Collins Sydney M , Cunningham Emma , Danielsen Jóhannis , Daunt Francis , d’Entremont Kyle JN , Doiron Parker , Duffy Steven , English Matthew D , Falchieri Marco , Giacinti Jolene , Gjerset Britt , Granstad Silje , Grémillet David , Guillemette Magella , Hallgrímsson Gunnar T , Hamer Keith C , Hammer Sjúrður , Harrison Katherine , Hart Justin D , Hatsell Ciaran , Humpidge Richard , James Joe , Jenkinson Audrey , Jessopp Mark , Jones Megan EB , Lair Stéphane , Lewis Thomas , Malinowska Alexandra A , McCluskie Aly , McPhail Gretchen , Moe Børge , Montevecchi William A , Morgan Greg , Nichol Caroline , Nisbet Craig , Olsen Bergur , Provencher Jennifer , Provost Pascal , Purdie Alex , Rail Jean-François , Robertson Greg , Seyer Yannick , Sheddan Maggie , Soos Catherine , Stephens Nia , Strøm Hallvard , Svansson Vilhjálmur , Tierney T David , Tyler Glen , Wade Tom , Wanless Sarah , Ward Christopher RE , Wilhelm Sabina , Wischnewski Saskia , Wright Lucy J , Zonfrillo Bernie , Matthiopoulos Jason , Votier Stephen C 
Published: May 2023

During 2021-22 High Pathogenicity Avian Influenza (HPAI) killed thousands of wild birds across Europe and North America, suggesting a change in infection dynamics and a shift to new hosts, including seabirds. Northern Gannets (Morus bassanus) appeared especially severely impacted, but limited understanding of how the virus spread across the metapopulation, or the demographic consequences of mass mortality limit our understanding of its severity. Accordingly, we collate information on HPAIV outbreaks across most North Atlantic gannet colonies and for the largest colony (Bass Rock, UK), provide impacts on population size, breeding success, adult survival, and preliminary results on serology. Unusually high numbers of dead gannets were first noted in Iceland during April 2022. Outbreaks in May occurred in many Scottish colonies, followed by colonies in Canada, Germany and Norway. By the end of June, outbreaks had occurred in five Canadian colonies and in the Channel Islands. Outbreaks in 12 UK and Ireland colonies appeared to follow a clockwise pattern with the last infected colonies recorded in late August/September. Unusually high mortality was recorded at 40 colonies (75% of global total colonies). Dead birds testing positive for HPAIV H5N1 were associated with 58% of these colonies. At Bass Rock, the number of occupied sites decreased by at least 71%, breeding success declined by ∼66% compared to the long-term UK mean and adult survival between 2021 and 2022 was 42% lower than the preceding 10-year average. Serological investigation detected antibodies specific to H5 in apparently healthy birds indicating that some gannets recover from HPAIV infection. Further, most of these recovered birds had black irises, suggestive of a phenotypic indicator of previous infection. Untangling the impacts of HPAIV infection from other key pressures faced by seabirds is key to establishing effective conservation strategies for threatened seabird populations, HPAIV being a novel and pandemic threat.