IRIS PIGMENTATION IRREGULARITIES FOLLOWING AN AVIAN INFLUENZA OUTBREAK: IMPLICATIONS FOR DISEASE SURVEILLANCE AND POPULATION MONITORING IN A COLONIAL SEABIRD

Emerging infectious diseases can have catastrophic impacts on wildlife populations, yet identifying individuals that survived exposure, especially when external symptoms are absent, remains challenging. Since 2021, a virulent strain of highly pathogenic avian influenza virus (HPAIV H5N1 clade 2.3.4.4b) has caused unprecedented mortality in wild birds across continents. Northern Gannets ( Morus bassanus ) are among the species that suffered significant population declines in Europe and North America. At North America’s largest gannet colony (Bonaventure Island) dramatic mortality and reproductive failure occurred in 2022. Following this event, researchers noted a subset of gannets displaying irregular iris pigmentation, raising the possibility that this visible change may indicate a lasting effect of infection. Here, we build on earlier observations linking irregular iris pigmentation to HPAIV exposure in gannets using anti-nucleoprotein (NP) and anti-hemagglutinin (H5) antibodies. This provides the first quantitative test of this relationship using serological data and field-based digital photography. Iris irregularities were strongly associated (ρ = –0.72) with antibodies to NP, supporting the hypothesis that they can indicate past exposure. The likelihood of NP antibody detection increased with iris pigment irregularity—about 50% likelihood at 40% irregularity, 65% at 50%, 77% at 60%, and over 90% above 77% irregularity. Moderate correlations (ρ = 0.30) were observed for H5 antibodies. Our findings provide quantitative support for the hypothesis that iris pigmentation irregularities may serve as a visible, non-invasive marker of past HPAIV exposure in gannets. If validated across colonies and years, iris assessment could offer a rapid tool for tracking population health and recovery following HPAIV outbreaks, enhancing conservation monitoring and disease surveillance.