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

Highly pathogenic avian influenza (HPAI) H5N1 caused mass seabird mortality across the North Atlantic in 2022. Following outbreaks in Europe, the first case in North America was detected on the island of Newfoundland (NFLD), Canada in November 2021, before spreading through all North American flyways. During the following breeding season, NFLD experienced the second-highest number of seabird mortalities in Canadian provinces. Surveys and citizen reports identified 13543 seabird mortalities from April to September 2022. Many carcasses occurred on the west coast of NFLD in May and June 2022. Reported mortalities peaked in July along the southeastern coast. In August and September, mortalities were concentrated along the northeastern coast. With the exception of two colony surveys, reported mortalities decreased in September. Most mortality was found among Northern Gannet (6622), Common Murre (5992), Atlantic Puffin (282), and Black-legged Kittiwake (217). Using comprehensive knowledge of seabird ecology, we formulated exploratory hypotheses regarding traits that could contribute to mortality. Species differences in mortality were most strongly associated with nesting density, timing of breeding, and at-sea overlap with allospecifics from other colonies. Unprecedented seabird mortality and ongoing transmission within the circulating avian influenza viruses highlight the need for continued monitoring and development of conservation strategies. ### Competing Interest Statement The authors have declared no competing interest.