The iris of avian flu survivors turns from blue to black

The bright blue irises of northern gannets turn black if they have had bird flu. This is stated in the study, which indicates that some wild birds get rid of the deadly virus.

Avian influenza has been killing wild and domestic birds for decades, but the current strain (H5N1) has severely impacted seabird populations in the North Atlantic. Last year, the mortality rate among gannets was especially high.

Scientists from several organizations have investigated the timing of outbreaks of avian influenza in colonies across their North Atlantic range, examining the impact of the virus in detail in Scotland, home to the world’s largest colony of gannets.

Black irises – instead of blue – were first seen on gannets breeding in Scotland last June, ranging in color from completely black to spotted.

The researchers took blood samples from 18 apparently healthy adult gannets with both normal and black irises. The samples were tested for avian influenza antibodies to determine if the birds had previously been infected. Eight tested positive, of which seven had black irises.

Dr. Jude Lane, RSPB conservationist and lead author of the study, said the significant finding is that gannets that have survived an avian flu infection no longer have their usual iris coloration. This can prove to be a useful non-invasive diagnostic tool.

“The next steps are to see if there are any detrimental effects on bird vision,” indicated scientist. “Ophthalmic examinations will also be required to determine what is causing the black coloration,” the researcher added.

The study was carried out in collaboration between the RSPB, the University of Glasgow, the University of Edinburgh, Heriot-Watt University and the Animal and Plant Health Agency in partnership with the Scottish Seabird Centre.