A highly contagious strain of avian flu continues to move west across North America this spring — an unprecedented source of mortality for wild birds as well as millions of chickens and turkeys in poultry plants and farms. Lately, the virus has been detected in wild birds in Wyoming and Montana and in backyard poultry flocks in Idaho and Utah.

Since late 2021, avian flu has been found in about 40 species of wild birds in the U.S. and Canada, says Bryan Richards, emerging disease coordinator at the Wisconsin-based National Wildlife Health Center. More than 700 individual wild birds have tested positive for highly pathogenic avian influenza (HPAI). The majority have been waterfowl, while others have been raptors and scavenging species like gulls, vultures, and Bald Eagle.

Wildlife rehab facilities have revamped their operations due to the outbreak because infected birds can easily spread the virus to other birds in a care facility. So, most rehabbers are isolating their feathered patients, and many have changed how they accept birds that are brought in by the public.

Raptors that catch the virus have “a 90 to 100 percent fatality rate,” says Victoria Hall, executive director of The Raptor Center at the University of Minnesota.

Infected birds of prey may have scavenged or hunted an infected duck or other animal. “But this virus is extremely hearty,” Hall says, “and in cool, wet conditions, it can last weeks and weeks in the environment. So, the bird doesn’t necessarily even have to come in contact with the duck that’s shedding the virus. It can just go to a place where there’s goose or duck poop and get exposed as well.”

‘It kills them pretty quickly’

Eagles and other birds of prey that have been brought to the center in recent weeks often have seizures or are nonresponsive, Hall says. “They’re just sitting with their heads down. We also have seen that it kills them pretty quickly.”

The New York Times reported yesterday that more than 40 Bald Eagles have died from avian flu. Krysten Schuler, the co-director of the Cornell Wildlife Health Lab, tells the Times what worries her about eagles: “I’m concerned it will be endemic, and there’s already been reports of some recombination, which means there’s this new strain mixing with some of the North American versions we have and creating new viruses. We always worry about those.”

A statement from the Georgia Department of Natural Resources says that aerial surveys show that nest success for eagles along the coast is down about 30 percent this year. Although the 73 nests documented was normal, Bob Sargent, a program manager with DNR’s Wildlife Conservation Section, said fewer than half fledged young, compared to an annual average success rate of 78 percent from 2015-2021.

Sargent added the eagle population in Georgia is strong, and he does not expect HPAI to significantly slow the species’ rebound. Initial survey results of eagle nesting outside the coastal region indicate a success rate on par with previous years. Full survey results are expected by late spring.

In Ohio, Richards says, one rehab facility took in 10 or 12 Bald Eagles in a four-week period, and most of them died. Normally, that rehabber would only see 10 or 12 eagles in a whole year, and most would recover and be released.

Still, he doesn’t foresee the virus taking a widespread toll on the populations of any North American bird species. Bald Eagle numbers, for example, soared in the last decade to an estimate of 316,700 individuals in the lower 48 states alone.

Distribution of Highly Pathogenic Avian Influenza H5 and H5N1 in North America, 2021/2022. Updated April 21, 2022. Source: USGS National Wildlife Health Center

The Raptor Center’s Hall, however, isn’t sure what impact avian flu will have on populations.

“We’re seeing much more mortality in wildlife, and at The Raptor Center we have seen at least a handful of complete nest failures of Great Horned Owls where the parents and the babies have all been found deceased because of avian influenza. So, this is starting to change our thoughts on what impact this could have. That’s part of the reason that at The Raptor Center we’re doing such complete surveillance and trying to track where the public has found deceased birds so we can start to get an idea of what this is actually doing to the population, because when we start losing whole breeding pairs and offspring together, that does make me concerned.”

Avian flu and bird feeders

As we reported recently, messaging from wildlife experts has been mixed about whether people should continue to provide birds with feeders and bird baths at this time. Most cases of the virus have been found in species that don’t visit feeders — waterfowl, raptors, gulls. However, two Blue Jays in Nova Scotia tested positive, and two Cooper’s Hawks — birds that hunt backyard songbirds — have also tested positive.

Also, an American Crow in North Dakota was found to be positive, and another has been reported dead in Minnesota, writes BirdWatching Contributing Editor Laura Erickson.

Hall says the uncertainty over feeders is the “million-dollar question” because it comes up a lot. “I’m a veterinarian and an epidemiologist as well as director of the center and you know, my philosophy is when we have this much disease in wild birds, anything we can do to stop birds of any species from gathering because of a human cause, such as bird feeding or bird baths, it’s probably a good idea right now.

“And especially as temperatures are warming up and we know songbirds are going to have other food sources out there available to them, so taking down feeders for a couple months could only help. The good news is it’s going to be a short-term thing. Usually, these outbreaks peter out in the summer, so it would just be for a couple of months. During this time of unprecedented transmission, it’s something we can do to help the birds.”

On April 13, The Raptor Center shared more thoughts about feeders and HPAI in this Facebook post, which has been shared thousands of times.

Hall says her caution over feeders extends to hummingbird feeders, because like all birds, hummingbirds may contract this virus. But she notes that very little is known in general about the incidence of HPAI in songbirds and hummingbirds.

Erickson, writing on her blog, says she’s taking down her tray feeders, but she’s continuing to use suet feeders and scatter seed on the ground and will put out her hummingbird feeders, unless she learns of hummingbirds contracting HPAI.

Richards, from the National Wildlife Health Center, says it’s fine if people want to take down feeders and baths for the time being, as a precaution against bringing together species that normally wouldn’t come close to each other in the wild. But, he notes, that there is little evidence that passerines are threatened by HPAI to a broad degree.

In the last HPAI outbreak in North America, in 2014-15, only two known songbirds tested positive: a European Starling and a Black-capped Chickadee. And this year’s known toll are the jays and crows noted above. “I’m not sure the science and data support a broad involvement of passerines in this outbreak,” says Richards.

He adds, however, that people should frequently clean and disinfect their feeders and baths, not just during this outbreak but all the time. Feeders and baths should be cleaned with a bleach solution, outside your house when possible. If you clean them indoors, use a laundry sink or bathtub, and thoroughly clean and disinfect the area right after.

Virus likely to fade over summer then return in fall

This past winter, HPAI killed thousands of Common Cranes in the Hula Valley in Israel. The mass mortality raised fears for North America’s Sandhill Cranes as they migrate north and the small population of Whooping Cranes that stop in some of the places that Sandhills do, including along Nebraska’s Platte River.

Richards says that the virus was found in a backyard poultry flock less than 10 miles from the Platte this spring, but “not a single crane that we know of contracted the virus” while they were in Nebraska. One difference from the situation in Israel is that artificial feeding keeps the Common Cranes concentrated in a relatively small area, which likely contributed to the large number of deaths. Artificial feeding doesn’t occur in Nebraska, so, while Sandhills are certainly close to each other when they roost on the river, they spread out into nearby fields during the day.

Like Hall, Richards also expects the virus to fade over the summer but says it’s likely to come back in the fall and winter. Waterfowl hunting begins in many states with teal season in September, and he says that birds collected at that time will be tested and will give scientists the first clues about what lies ahead with avian flu.