Bald Eagle Numbers Hit by Avian Flu
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Bald eagles are often touted as a massive conservation success story due to their rebound from near extinction in the 1960s.
But now a highly infectious virus may put that hard-fought comeback in jeopardy.
Published in Nature’s Scientific Reports, new research from the University of Georgia showed highly pathogenic avian influenza, also known as H5N1, is killing off unprecedented numbers of mating pairs of bald eagles.
“Even just one year of losses of productivity like we’ve documented regionally is very concerning and could have effects for decades to come if representative of broader regions,” said Nicole Nemeth, lead author of the study and an associate professor in the College of Veterinary Medicine. “There were nights where I couldn’t sleep based on what we were hearing and seeing. We have already lost unprecedented numbers of wild birds due to this virus in the U.S. and it appears here to stay.”
Less than half of Georgia bald eagle nests fledged one chick in 2022
The researchers found that just under half of bald eagle nests along coastal Georgia successfully fledged at least one eaglet in 2022. That’s 30% below average for the region.
The study also showed the success rate for nests was halved in one Florida county, dropping to 41% from an average of 86.5%. Another Florida county experienced a less dramatic but still concerning decrease from an average of approximately 78% to 66.7%.
“We had reports from people who faithfully monitor eagle nests year after year with these heartbreaking stories of an adult eagle found dead below their nest. Within a few days, often its mate and the chicks were also found dead below the nest. It is clear the virus is causing nest failures,” said Nemeth, who is part of the UGA-based Southeastern Cooperative Wildlife Disease Study (SCWDS).
The collaboration is the first diagnostic and research service established specifically to investigate wildlife diseases.
Number of infected wild birds likely an undercount
In April 2022, SCWDS researchers confirmed highly pathogenic avian influenza had hit Georgia’s eagle populations for the first time.
The three dead eagles were found in Chatham, Glynn and Liberty counties in March.
At the time, the U.S. Department of Agriculture (USDA) had confirmed around 660 cases of the H5N1 virus in wild birds, only 11 of which were from Georgia.
That number has since skyrocketed to more than 6,200 reported cases across the country, according to the USDA’s Animal and Plant Health Inspection Service.
Those cases include a variety of vultures and other raptors, waterfowl like geese and ducks, as well as other aquatic birds like pelicans and herons, and even some songbirds, though they are less common victims of the virus. (Tens of millions of commercially farmed poultry have died or been culled due to risk of infection.)
“I think the number of wild bird cases is drastically underreported,” Nemeth said. “People will submit one snow goose, for example, and it will test positive for the virus. And then they’ll tell you, ‘Well, there are thousands of geese dying at the same site.’ But it only goes down as one infected bird.”
H5N1 doesn’t pose massive threat to humans but may to other species
The birds at biggest risk of infection are those that live in coastal or other aquatic areas inland or prey on other birds that do.
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The virus can persist in water for over a year, given the proper conditions. While not a risk to people, birds can pick up the virus from spending time in the water and carry it to new locations through migration.
Raptors like eagles and vultures then catch the virus when they consume the infected birds.
“Worst case scenario, we get into a scary place with some of these bird species,” Nemeth said. “We could see a lot more decline in the numbers of eagles, raptors, waterfowl and other birds than what we’ve already seen. It could be devastating.”
Bears, red foxes and coyotes among animals infected with virus
Avian influenza has hopped species as well.
H5N1 has infected wild mammals such as red foxes, coyotes, racoons, seals, opossums and even some bears in North America. However, very few people have been infected with the virus in the U.S. and have recovered with minimal symptoms, according to the Centers for Disease Control and Prevention.
“A virus that can spread and be maintained as this virus can, it’s everywhere now,” Nemeth said. “We can’t contain the virus, and we can’t vaccinate wild birds. But we can document the losses and try to help conserve affected species and populations the best we can.”
Reference: Nemeth NM, Ruder MG, Poulson RL, et al. Bald eagle mortality and nest failure due to clade 18.104.22.168 highly pathogenic H5N1 influenza a virus. Sci Rep. 2023;13(1):191. doi:10.1038/s41598-023-27446-1
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