Wild bird mass mortalities in eastern Canada associated with the Highly Pathogenic Avian Influenza A(H5N1) virus, 2022

Abstract

In 2022, a severe outbreak of clade 2.3.4.4b Highly Pathogenic Avian Influenza (HPAI) H5N1 virus resulted in unprecedented mortality among wild birds in eastern Canada. Tens of thousands of birds were reported sick or dead, prompting a comprehensive assessment of mortality spanning the breeding season between April 1 and September 30, 2022. Mortality reports were collated from federal, Indigenous, provincial, and municipal agencies, the Canadian Wildlife Health Cooperative, non-governmental organizations, universities, and citizen science platforms. A scenario analysis was conducted to refine mortality estimates, accounting for potential double counts from multiple sources under a range of spatial and temporal overlap. Correcting for double counting, an estimated 40,966 wild birds were reported sick or dead in eastern Canada during the spring and summer of 2022. Seabirds and sea ducks, long-lived species that are slow to recover from perturbations, accounted for 98.7% of reported mortalities. Mortalities were greatest among Northern Gannets(Morus bassanus; 26,193), Common Murres (Uria aalge; 8,133), and American Common Eiders (Somateria mollissima dresseri;1,945), however, these figures underestimate total mortality as they exclude unreported deaths on land and at sea. In addition to presenting mortality estimates, we compare mortalities with known population sizes and trends and make an initial assessment of whether population-level impacts are possible for the Northern Gannet, a species that has suffered significant global mortality, and two harvested species, Common Murre and American Common Eider, to support management decisions. We hypothesize that population-level impacts in eastern Canada are possible for Northern Gannets and American Common Eiders but are unlikely for Common Murres. This study underscores the urgent need for further research to understand the broader ecological ramifications of the HPAI outbreak on wild bird populations.

Seabird and sea duck mortalities were lower during the second breeding season in eastern Canada following the introduction of Highly Pathogenic Avian Influenza A H5Nx viruses

“…We defined spring/summer as April 1 – September 30, which spans the breeding season for almost all birds in eastern Canada. To quantify the differences in mortality across the breeding seasons across two years, we present data for i) the spring/summer of 2022 (the period reported in Avery-Gomm et al 2024) and ii) the spring/summer of 2023. In addition, we report mortalities for the intervening period (October 2022 – March 2023), hereafter referred to as the fall/winter period.…”

“…In addition, we report mortalities for the intervening period (October 2022 – March 2023), hereafter referred to as the fall/winter period. Deviations from the methods described by Avery-Gomm et al (2024) included an increased effort to survey beaches in the spring/summer of 2023, the inclusion of the complete mortality dataset (i.e., not only HPAI- linked mortality), and no effort to characterize the age classes of any species using photos submitted to iNaturalist.…”

“…The impact of highly pathogenic avian influenza (HPAI) clade 2.3.4.4b H5N1 viruses and their derived reassortants (H5Nx) on both wild and domestic birds in recent years has been unprecedented (Careen et al, 2024; Lane et al, 2023; Ramey et al, 2022). This virus has also been responsible for disease and mortality events in an unprecedented number of wild bird species worldwide (Avery-Gomm et al, 2024; Leguia et al, 2023; Molini et al, 2023; Rijks et al, 2022). Another concerning development with this virus has been the positive detection in a wide variety of marine mammals and terrestrial mesopredators (Alkie et al, 2023; Plaza et al, 2024).…”

“…Since then, mass mortality events in seabirds (e.g., Pelecaniformes, Suliformes, and Charadriiformes), sea ducks (e.g., American Common Eider; Somateria mollissima ), and geese (Anseriformes; waterfowl) have been documented (Avery-Gomm et al, 2024; Giacinti et al, 2023). To date, the largest mortalities associated with HPAI in North America have been in eastern Canada, where at least 40,391 wild birds died during the 2022 HPAI outbreak between April and September 2022 (Avery-Gomm et al, 2024). The scale of mass mortality that occurred among seabirds and sea ducks was unanticipated and coincided with similar mass mortalities in Europe (European Food Safety Authority et al, 2022; Pearce-Higgins et al, 2022).…”

Geographic, ecological, and temporal patterns of seabird mortality during the 2022 HPAI H5N1 outbreak on the island of Newfoundland

“…Observations of the same species reported two or more times within 1 km and 1 day (i.e., potentially double-counted records) were identified and removed from the dataset. A complete description of the data collation methods and processing can be found in Avery-Gomm et al (2024). For the present study, we extracted reports of seabird mortalities (Fig.…”