Anti-H5 antibody prevalence was lower in common eider in NU with 0% (037.1%) in Arviat and 28.6% (9.658%) in Iqaluit. Anti-NP antibodies in black guillemot eggs in 2023 were widely detected across sites (Fig. eastern Canada and two from western Iceland. The prevalence of AIV antibodies in eggs varied across regions, species and years. American common eider (Somateria mollissima dresseri) eggs experienced the highest AIV antibody prevalence compared to sympatric species in 2023. Longitudinal samples were available for northern gannets (Morus bassanus) and American herring gulls (Larus argentatus smithsoniansus) at several sites, where the SP600125 prevalence of anti-NP and anti-H5 antibodies increased from 2022 to 2023. Examining AIV antibody prevalence in seabird eggs can be a useful tool to investigate population-level AIV exposure, while we acknowledge our limited understanding of differential antibody waning rates and the relationship between titre and susceptibility. Keywords:Antibodies, avian influenza computer virus, birds, H5n1, surveillance, wildlife monitoring == Introduction == Seabirds are one of the reservoirs of avian influenza viruses (AIV), which prior to 2021 nearly entirely comprised low pathogenic AIV (LPAIV) with limited morbidity and mortality (Langet al., 2016). The H5N1 clade 2.3.4.4b was introduced to North America via the Atlantic and Pacific flyways following a significant Western epizootic (Alkieet al., 2022;Rameyet al., 2022;Alkieet al., 2023;Rahmanet al., 2024), resulting in elevated disease and mortality in wild birds, marine mammals, domestic birds, cattle and terrestrial mammals (WOAH, 2025). Unlike previous H5Nx outbreaks, HPAIV has persisted in wild bird populations, with elevated morbidity and mortality rates in seabird species globally (Laneet al., 2023;Avery-Gommet al., 2024). Given the Arf6 ongoing common, broad host diversity and high mortality of HPAIV in wild birds, there is a growing need to understand the spatiotemporal extent of AIV and HPAIV exposure and its effects in wild birds. Seabirds are of particular interest as they can mediate transcontinental computer virus incursions (Caliendoet al., 2022), have an affinity for agricultural landscapes (Gartheet al., 2022), interact with people in urban environments (de SP600125 Fariaet al., 2022) and are hunted for subsistence and feathers (Denlinger and Wohl, 2001;Montevecchiet al., 2007;Bdardet al., 2008;Natcheret al., 2012). Introductions of clade 2.3.4.4b from 2021 to 2023 to North America have drastically altered disease ecology in seabirds (Banyardet al., 2022;Laneet al., 2023). Since 2022, variance in viral detection (Giacintiet al., 2024a) and disease impacts at individual and population levels (Laneet al., 2023;Avery-Gommet al., 2024) among species and regions have been well documented. In 2021, great skuas (Stercorarius skua) in the UK displayed unusually elevated H5N1-attributable mortality at several colonies, but few other colonial seabirds showed clinical indicators of contamination (Banyardet al., 2022). In 2022, H5N1 was detected in dozens of seabird species in the North Atlantic, with mass mortality events reported for northern gannets (Morus bassanus), common murres (Uria aalge), common eiders (Somateria mollissima;Avery-Gommet al., 2024) and Sandwich terns (Thalasseus sandvicensis;Rijkset al., 2022). Local, regional and national reports of H5N1 in seabirds have highlighted how seabird species may be differentially uncovered and susceptible to HPAIV. Exposure to influenza A computer virus (IAV) results in cell- and antibody-mediated adaptive immune responses and immune memory that can aid in response to subsequent infections (Dohertyet al., 2009). Serum can be used to detect antibodies in wild birds, e.g. SP600125 against the conserved nucleoprotein (NP) and variable hemagglutinin (HA) surface protein; however, obtaining blood samples from migratory bird species, including seabirds, can be challenging. Eggs are easier to collect and contain maternal antibodies packaged during egg formation that provide passive immune protection (van Dijket al., 2014). While the transfer of maternal antibodies has been detected in several species, only a few studies have evaluated the relationship between.