The irises of Northern Gannets, a type of seabird, turn black if they recover from highly pathogenic H5N1 avian influenza, according to a new pre-print study published last week.
Northern Gannets were one of the species severely impacted by the ongoing bird flu outbreak affecting Europe and the Americas.
The study, which has not yet been peer-reviewed, examined Gannets at Bass Rock in the UK, after researchers noticed that some of the seabirds had unusual black irises instead of the usual blue.
The researchers took blood samples from 18 apparently healthy adult Gannets with both normal and black irises and tested the samples for bird flu antibodies. Eight of the birds tested positive, seven of which had black irises.
The scientists noted that black irises may serve as a likely indicator of prior infection with avian influenza. The researchers added that the one infected bird with blue irises may have been infected with a different subtype of avian influenza, waning antibody levels or it may be that not all infected birds develop black irises.
Two additional birds with black irises tested negative for the virus, with the researchers suggesting that the birds may have been previously infected but had already lost the antibodies.
Black eyes have been reported in gannets once before, although the reason is unknown. Gannets with black irises have also been reported in other colonies in the UK, France, Germany and Canada.
“This has been a fascinating development and the discovery may prove a useful non-invasive diagnostic tool," said Dr. Jude Lane, a conservation scientist at the Royal Society for the Protection of Birds (RSPB) and lead author of the study. "The next steps are to understand its efficacy, if it applies to any other species and whether there are any detrimental impacts to the birds’ vision. Ophthalmology exams will also be needed to determine what is causing the black coloration.”
According to the RSPB, outbreaks of avian influenza were recorded last year in Iceland, Scotland, Canada, Germany and Norway, including at Bass Rock, the world's largest Gannet colony.
The researchers found that the estimated survival of adult birds was 42% lower than the preceding 10-year average, although the full extent of mortality among the birds won't be confirmed until the birds come back this breeding season.
“Like many northern gannet colonies across the North Atlantic the Bass Rock was severely impacted in 2022 by highly pathogenic avian influenza," said Susan Davies, CEO of the Scottish Seabird Center. "Due to the long running research effort on the Bass Rock, it was possible to gain important insights into the changes taking place in the colony with a strong link emerging between virus infection and the changing iris color in these striking seabirds and the high level of nest failure within the study area.”
The study was conducted by researchers from the RSPB, the University of Glasgow, the University of Edinburgh, Heriot Watt University and the Animal Plant Health Agency in partnership with the Scottish Seabird Centre.
In the past two years, large outbreaks of the H5N1 subtype have spread across Europe and the Americas in what has been described as "the largest-ever" outbreak on both continents, with additional outbreaks reported across the world. In recent months, increasing numbers of mammals have been found to be infected with the virus, with mass die-offs of seals and sea lions reported in Russia and the Americas and dozens of foxes, skunks, dolphins, raccoons and cats found to be infected as well.
The outbreak has been widely affecting both birds and mammals. In the US alone, over 58 million poultry have been affected and 6,715 infected wild birds have been found in almost every state. In Europe, thousands of wild and domestic birds were found to be infected in over 24 countries, with many sea birds affected.
Avian flu killed twice as many wild birds in UK as previously estimated
Additionally, on Friday, The Guardian found that avian influenza has killed more than twice the number of wild birds previously estimated, with at least 50,000 wild birds affected by the outbreak.
The British Trust for Ornithology (BTO) estimated that “many more than 20,000” wild birds had died in the UK since the current outbreak began about a year and a half ago in October 2021, but the Guardian studied data from regional governments and nature organizations and found that at least 50,000 birds died due to the bird flu from October 2021 to April 2023.
Even this number is likely to still be a gross underestimate, as there is no national monitoring in the UK and most carcasses are never found or counted, according to The Guardian.
Russia accuses US of 'studying ways to spread bird flu'
Additionally, on Friday, the chief of Russia's Radiation, Chemical and Biological Protection Force, Igor Kirillov, accused the Pentagon of working through Ukraine's Science and Technology Center to assess the conditions which would cause the uncontrolled spread of bird flu in the Azov-Black Sea region, according to TASS.
TASS reported the claim with the headline "Pentagon studied ways to spread bird flu via Ukrainian center, top brass says."
Kirillov claimed that a project called P-444 monitored avian influenza among wild birds in the region and assessed "under what conditions the virus’ transmission would become uncontrolled, cause economic damage and create risks for food security."
Throughout the Russian invasion of Ukraine, Russian authorities and media have repeatedly published claims that Ukrainian and American authorities were conducting "military-biological projects," including biological weapons research. The claims have been widely spread by conspiracy theorists on social media and some talk shows.