In a shocking epidemiological study, researchers have revealed that a staggering 56% of a significant breeding colony of Caspian terns at Rat Island, Washington, fell victim to a severe outbreak of highly pathogenic avian influenza (H5N1) in 2023. This alarming discovery has sparked concerns about the already dwindling Pacific-coast population of these seabirds, as no successful breeding has taken place on the island since the outbreak.

This outbreak serves as a grim wake-up call for wildlife conservationists. A multidisciplinary team involving the Washington Department of Fish and Wildlife (WDFW) and Washington State University researchers uncovered the devastating effects of this avian flu strain, which remarkably jumped from terns to harbor seals for the first time in the northeastern Pacific.

Since the outbreak, there has been a relative calm regarding H5N1 in coastal wildlife, yet experts estimate that around 10% to 14% of the Pacific flyway's Caspian tern population has perished due to infections related to this strain. "The impact of this avian flu on Caspian terns, a species already in decline, is significant and troubling," stated Katherine Haman, WDFW wildlife veterinarian and lead study author, as published in the journal *Frontiers in Veterinary Science.*

Remarkably, Caspian terns are distributed across the U.S. The largest breeding colony was traditionally found in the lower Columbia River, downstream of Portland. However, conservation efforts to protect endangered salmon led to the birds being pushed away from their original nesting sites. Many of these terns likely migrated to Rat Island, a choice that tragically coincided with the 2023 outbreak.

Community involvement played a crucial role in addressing the outbreak. Volunteer docents from the Friends of Fort Flagler and local kayaking guides were alert to the first signs of bird deaths, allowing for prompt action by researchers who collected carcasses and euthanized afflicted birds. This proactive approach unfortunately led to the deaths of an estimated 1,101 adult terns and 520 chicks.

Even more surprising, additional investigations reported 15 deceased harbor seals in the vicinity, whereas only one or two deaths are typical in an average year. Initial tests indicated that the seals did not contain H5N1 in respiratory samples, leading researchers to dig deeper. "It seemed odd because there was a considerable mortality in the seals correlated with concurrent bird deaths," noted Kevin Snekvik, co-author and a veterinary pathologist at WSU. Subsequent testing revealed inflammation in seals’ brains, a unique response to the virus.

Globally, avian influenza has wreaked havoc among seals and sea lions, especially in South America, yet the Pacific Northwest has yet to experience a similar widespread outbreak among marine mammals. The situation remains precarious for the Caspian terns of this region, which face uncertain futures.

Currently, there is no vaccine or treatment for animals affected by avian flu in the U.S., making it challenging to control the rapid spread in wildlife populations. Efforts are shifting to understanding disease transmission and its ecological impact.

While human cases of avian flu have mostly been confined to agricultural workers with close contact to infected domestic animals, the risk remains a topic of ongoing research and concern, especially among wildlife professionals and public health officials.

**Stay tuned as we continue to follow developments in this ongoing crisis that could reshape the future of wildlife on the Washington coast!**