Climate change and nutrient deficiency in the seas have for a long time caused problems for several seabird species. Now, a new problem has been detected. During the last couple of years, an outbreak of High Pathogenicity Avian Influenza has killed thousands of seabirds. Scientists have now investigated the outbreak of avian flu in Northern Gannets Morus bassanus and examined its effect on adult survival and breeding success. The results are far from encouraging.

Lethal virus

In 2021 and 2022, 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 appeared to be especially severely impacted, but a detailed account of the data available was required to help understand how the HPAI virus (HPAIV) spread across the meta-population, and the ensuing demographic consequences.

Spreading rapidly

The researchers behind a recently published article analyzed information on confirmed and suspected HPAIV outbreaks across most North Atlantic gannet colonies and, for the largest colony (Bass Rock, UK), provided impacts on population size, breeding success, and preliminary results on apparent adult survival and serology. Unusually high numbers of dead gannets were first noted at colonies 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 colonies in Canada and the English Channel.

Increased mortality and reduced breeding success

Unusually high mortality was recorded at 40 colonies (75% of global total colonies). Dead gannets testing positive for HPAIV H5N1 were associated with 58% of these colonies. At Bass Rock, the number of occupied nest-sites decreased by at least 71%, and breeding success declined by c. 66% compared with the long-term UK mean. The resighting of marked individuals suggested that apparent adult survival between 2021 and 2022 could have been substantially lower than the preceding 10-year average.

Black iris a possible phenotypic indicator

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 challenges faced by seabirds is key to establishing effective conservation strategies for threatened seabird populations.

Read the article:

Northern gannets in a breeding colony. Photo © Rob Barrett
Northern gannets breed in relatively dense colonies but stay out at sea in the non-breeding season.
Photo © Rob Barrett
A Northern gannet close-up. Photo © Rob Barrett
The gannet’s iris (the area around the pupil) is normally pale blue.
Photo © Rob Barrett

Contact person: Signe Christensen-Dalsgaard, NINA