A pair of Caspian terns. (Gary Rogers/Getty Images)
More than half a colony of Caspian terns on a small island near Port Townsend died last year amid an outbreak of bird flu, underscoring the harsh effects the disease can have on wildlife.
Researchers say they directly counted 1,101 dead adult terns and 520 dead chicks and that at least 53-56% of the adult birds in a colony on Rat Island, in northern Puget Sound, were wiped out. After factoring in Caspian tern deaths in other parts of the region, the researchers estimated about 10-14% of the birds in the Pacific flyway were lost last year to bird flu.
The researchers also studied harbor seals that died from the virus on or around Rat Island during the same timeframe and found that the disease had attacked the animals differently than it did birds, causing severe inflammation in their brains.
A team that included staff from the Washington Department of Fish and Wildlife and Washington State University published the findings in Frontiers in Veterinary Science. Researchers from about a half-dozen other organizations and universities also worked on the study.
“This Caspian tern event was the first big marine environment avian flu outbreak for Washington. It caused a significant, punctuated mortality for the Caspian terns, which were already a species in decline throughout this flyway,” said Katherine Haman, a wildlife veterinarian at the Department of Fish and Wildlife and lead author on the study.
Caspian terns are migratory and return to the Northwest in late April or May after wintering elsewhere, mostly in southern California and Mexico. They can live for 20 years or more. The journal article cites estimates indicating that, in 2021, about 10,800 Caspian terns were living in the Pacific flyway — a major migratory bird corridor between North and South America.
Washington’s Department of Fish and Wildlife received the first reports of sick or dead Caspian terns on Rat Island in July last year. The researchers’ modeling suggests adult terns started dying from bird flu on the island around July 3. The outbreak stretched through the end of August, they said, and at its peak about 50 of the birds were dying per day.
In contrast to the high death rate for the terns, the researchers estimated that only about 3% of the island’s adult Glaucous-winged gulls died from the disease. Juvenile gulls were more vulnerable, with at least 298 of the young birds counted dead.
Flareup in Northwest
The findings come as bird flu — a virus formally known as H5N1 highly pathogenic avian influenza — has flared up this fall in Washington.
On Thursday, Woodland Park Zoo in Seattle said a red-breasted goose there had died from a suspected case of bird flu. The zoo had been taking precautions to protect animals and people from the disease, including draining pools of water in open-topped bird exhibits and moving free-roaming peacocks indoors. Now it plans to further tighten safety protocols.
Last month, the disease infected a flock of about 800,000 poultry at an egg farm in Franklin County, in southeast Washington. The birds there were euthanized and the eggs destroyed.
During the Franklin County outbreak, the disease jumped to people who worked around poultry at the farm. The U.S. Centers for Disease Control and Prevention last week listed 52 cases of bird flu nationwide, with 11 in Washington all tied to poultry. Officials confirmed a human case of the disease in Oregon on Friday that was linked to poultry as well.
The CDC says risks to humans from the bird flu remain low, especially for people who don’t work around animals that can spread it. A concern is that the virus could mutate in ways that allow it to spread from person to person. Health officials are also watching for signs that the disease is causing more severe illness in humans.
With the recent cases in Washington, health officials described patients having relatively minor symptoms, like runny noses, sore throats, and conjunctivitis or “pink eye.” But the disease has proven deadly in the past. Between 2003 and April this year, the World Health Organization recorded 889 human cases and 463 deaths in 23 countries caused by the H5N1 bird flu virus.
Virus harmed seals’ brains
The new research highlights how bird flu can affect different species in different ways.
With birds, it typically spreads to animals’ respiratory tracts. With 16 dead harbor seals documented on Rat Island and other locations nearby last year, testing showed the virus had harmed the animals’ brains as well as their lungs. Nasal swab tests for two of the dead harbor seals were negative but tests of lung or brain tissue were positive.
Testing discovered seals’ brains were inflamed with a condition known as meningoencephalitis as well as brain cell death, or neuronal necrosis.
“It took a little bit to figure that out,” said Kevin Snekvik, a professor at Washington State University and executive director at the Washington Animal Disease Diagnostic Laboratory. “Our initial samples were negative, but we knew these seals were dying.”
“It informs us that you need to be collecting and evaluating different samples in order to get the correct diagnosis,” he added.
Inflammation similar to what was seen in the seals’ brains has also been found previously in other carnivores that have caught the virus, including raccoons and skunks, Snekvik noted. There are theories that this could have to do with how the animals feed on infected carcasses. “We don’t know exactly why that is,” Snekvik said. “But it’s definitely showing up differently.”