The blue eyes of some seabirds appear to darken after being infected with bird flu.
The color change, observed in northern gannets (Morus bassanus), may give scientists a new way to track the impact of the virus outbreak.
Bird flu has seasonally circulated among wild and farmed birds for decades, but, since October 2021, a highly pathogenic strain of the virus has swept through wild and farmed bird populations with unusual virulence.
Seabirds in Europe and the UK have been particularly hard hit, with thousands dying last year from the H5N1 virus, including threatened gannets, puffins and great skuas.
The adult survival rate of the population of 150,000 gannets on Bass Rock, an island off the east coast of Scotland, for example, was 42% lower than average between 2021 and 2022.
Without performing invasive tests, scientists are struggling to say whether seabirds have suffered infections and survived or have so far escaped contact with the virus.
Collecting this information is crucial to better understand how the virus is affecting wild bird populations, including assessing survival rates and determining whether these birds are developing immunity to the disease.
Gannets with black or black-spotted irises, rather than the standard pale blue color, have been spotted for the first time in several colonies known to have been affected by bird flu, including the UK, France, in Germany and Canada.
Jude Lane from the RSPB, a UK conservation charity, and colleagues took samples from 18 apparently healthy gannets with normal, black irises living on Bass Rock. Eight of the birds tested positive for avian flu antibodies and, of these, seven had black irises.
The incidence of this trait could be a useful noninvasive diagnostic tool for conservationists tracking the impact of avian flu, Lane says. “Being able to see how many birds are dying, but also how many birds are surviving, will allow us to add those details into population models to predict what seabird populations might look like in the future,” says- She.
It’s unclear why irises turn black, but Lane and his colleagues are studying it. She also plans to study whether the change is permanent, how long antibodies to the virus persist in gannets, and whether the birds suffer any long-term adverse effects from the infection, such as fertility or birth problems. vision.
Understanding whether the same eye color changes occur in other bird species will also be crucial, she adds, although the feature may be harder to spot in those with naturally darker eyes. .