A recent epidemiological study revealed that 56% of a significant breeding colony of Caspian terns perished during a 2023 outbreak of highly pathogenic avian influenza on Rat Island in Washington state. Since this incident, there have been no successful breeding attempts by birds on the island, which raises concerns about the potential long-term effects on an already dwindling population along the Pacific coast.
The research team, which included members from the Washington Department of Fish and Wildlife (WDFW) and Washington State University (WSU), also discovered that the avian flu virus H5N1 had made its first known transfer to harbor seals in the northeastern Pacific.
Even though there haven’t been any new major outbreaks of H5N1 in coastal wildlife, researchers estimate that approximately 10-14% of the Caspian tern population in the Pacific flyway may have been lost due to H5N1 infections.
“This incident involving Caspian terns marked the first significant avian flu outbreak in Washington’s marine environment. It resulted in notable fatalities among Caspian terns, a species that was already experiencing decline across this flyway,” explained Katherine Haman, a wildlife veterinarian with WDFW and the primary author of this study published in the journal Frontiers in Veterinary Science.
Caspian terns are distributed throughout the United States, and until recently, their largest breeding ground was on an island in the lower Columbia River, downstream of Portland. Due to their consumption of juvenile endangered salmon, measures were taken to deter them from nesting on that island. It is believed that part of the large Columbia River colony relocated to Rat Island near Fort Flagler Park in Jefferson County, before the avian flu outbreak in 2023 occurred.
Haman credited the early detection of the first bird deaths on Rat Island to dedicated citizen volunteers from the Friends of Fort Flagler and local kayaking guides, who promptly informed officials. This swift action enabled researchers to respond quickly, allowing them to collect deceased birds and euthanize those showing symptoms. Ultimately, 1,101 adult birds and 520 chicks were lost to the outbreak.
The research team also observed 15 dead harbor seals in the vicinity, whereas the area typically reports only 1 or 2 seal deaths annually. Using tissue samples, researchers at Washington Animal Disease Diagnostic Laboratory (WADDL) successfully identified H5N1 in the birds, though confirming the presence of the virus in seals proved to be more challenging.
“While avian influenza is often regarded as a respiratory illness, the seal lung samples initially returned negative for H5N1. This was surprising given the high mortality among the seals, alongside concurrently sick birds,” noted co-author Kevin Snekvik, a veterinary pathologist at WSU and the executive director of WADDL.
Further examinations of other organs revealed that the avian flu virus caused an inflammatory response in the seals’ brains, indicating a different pathological effect. Whole genome sequencing of the virus confirmed that the seals likely contracted it from the terns.
While avian influenza has led to the deaths of many seals and sea lions in various parts of the world, particularly in South America, this type of spread has not yet been observed in the Pacific Northwest. Unfortunately, the impact on tern populations in this region has been more severe. Currently, there are no vaccines or treatments available in the U.S. for affected wildlife. Due to the rapid transmission and challenges associated with handling wild animals, researchers are focused on gaining insights into how the disease spreads among wildlife populations.
Human cases of avian flu in Washington and across the U.S. have mostly involved agricultural workers who had close contact with infected domestic animals, according to the Centers for Disease Control and Prevention.
The researchers stressed that it is important for people to avoid touching sick or dead wildlife and instead report any sightings on the WDFW website.
This study received funding from various entities, including the Washington state legislature, the Centers for Disease Control and Prevention, the National Oceanic and Atmospheric Administration, the Washington Department of Health, WDFW, and WADDL. The investigation benefitted from extensive collaboration with additional researchers from WSU, WDFW, Center Valley Animal Rescue, the National Marine Fisheries Service, Pennsylvania State University, the Washington Department of Health, and the University of California, Davis.
“The successful outcome of this study and the ongoing investigations can be attributed to numerous organizations working in unison. For wildlife research, effective collaboration across different groups is critical,” emphasized co-author Tom Waltzek, a researcher associated with WADDL and WSU’s College of Veterinary Medicine.
