Kleptoparasitism in seabirds-A potential pathway for global avian influenza virus spread

Wild birds have experienced unprecedented, near-global mass mortalities since 2021, driven by outbreaks of high-pathogenicity avian influenza virus (HPAIV) H5N1 lineage 2.3.4.4b. Managing this panzootic requires identification of transmission pathways. We investigated potential HPAIV transmission via kleptoparasitism (food theft) by examining the distribution, behaviors, and movements of two globally widespread and commonly kleptoparasitic seabird families: Fregatidae (frigatebirds) and Stercorariidae (skuas). These kleptoparasites force other seabirds (targets) to regurgitate food, which the kleptoparasite then ingests, potentially facilitating direct transfer of viral particles from target to kleptoparasite. Scavenging and predation probably contribute further to viral spread. Although frigatebirds use kleptoparasitism on a year-round basis, skuas more commonly do so outside of the breeding season. Both frequently forage, disperse, or migrate across oceans and hemispheres. Dense aggregations of kleptoparasitic and target seabirds at breeding and/or roosting sites may facilitate the spread of HPAIV. In addition, the migration of these species could also facilitate broadscale geographic spread of HPAIV. Surveillance of kleptoparasites for HPAIVs could aid in early detection and may be important for seabird conservation.