Officials on lookout for continuing signs of bird flu in wild and domestic flocks

As a historic outbreak of highly pathogenic avian influenza continues to circulate across most of the world this spring, wildlife officials continue to watch for signs of the disease among nesting birds and those migrating north as well as assist with efforts to develop a vaccine to fight the virus in endangered wild birds and commercial flocks alike.

In one hopeful sign, preliminary data show eaglets are surviving at a higher rate this year in Wisconsin bald eagle nests, according to a project organized by Madison Audubon, potentially indicating the disease is waning.

Since it was detected in North America in the winter of 2021, the H5N1 virus has spread throughout the U.S., into Mexico and Central and South America. It’s been documented in every state except Hawaii and on every continent except Antarctica and Australia, although many wildlife disease experts expect it to arrive there, too.

The virus has also affected mammals, including grizzly bears in Montana.

The outbreak is already the deadliest ever for U.S. poultry producers, affecting 58.8 million domestic birds, according to the U.S. Department of Agriculture.

It has surpassed the 2015 outbreak of subtype H5N2, which hit about 49 million birds at U.S. farms. At a cost of $1 billion, that outbreak was deemed the most costly animal health emergency in U.S. history, according to the USDA.

The financial losses associated with the current bird flu strain have yet to be tallied but are likely to exceed the previous outbreak.

H5N1 is deadliest bird flu ever documented among wild birds

The toll on wild birds is much more difficult to assess. However, all signs point to the outbreak of H5N1 over the last two years as the deadliest version of bird flu ever documented among wild birds.

"This (bird flu outbreak) is off the charts, the worst I've ever seen," said Sumner Matteson, a conservation biologist at the Wisconsin Department of Natural Resources who has worked on bird conservation projects for the last 41 years. "I've never seen a disease have such an immediate, disastrous impact like this one."

Birds that gather in flocks and breeding colonies are particularly affected by H5N1, as are raptors that scavenge on sick or dead birds infected with the virus.

Ducks, geese, swans, eagles, hawks, pelicans, cranes, gulls and terns are among the types of birds found dead and have tested positive for the H5N1 during the current outbreak.

Bird flu devastates Caspian tern population along the Door Peninsula

Last June, Matteson documented the loss of more than 1,000 Caspian terns to bird flu on two islands along the Door Peninsula in northeastern Wisconsin. The deaths were estimated at 64% of the breeding population of the state endangered species.

Matteson said it was the most disturbing experience he'd had in his career to be among scores of dead, sick and dying birds and realizing there was nothing he could do to help.

A dead Caspian tern was found in April along the Lake Michigan shore in Ozaukee County, a likely victim of bird flu, according to Matteson.

"This disease may not be as apparent this year, but it is still with us," Matteson said.

Matteson is scheduled to visit Door County in early June to check the status of breeding Caspian terns and other birds.

A sign of hope in Wisconsin seen among eagles nests

The virus was also linked last year to a marked drop in production of bald eagles in Wisconsin. The Bald Eagle Nest Watch program run by Madison Audubon found just 35% of 110 nests produced an eaglet to the fledgling stage in 2022. Over the previous four years the success rate was about 80%.

This year, however, the trend reversed, and 89% of active nests being monitored by volunteers had at least one eaglet as of late May, according to Brenna Marsicek of Madison Audubon. The year-over-year change documented in eagle productivity may provide a first glimpse of a reduced impact of the virus, at least in Wisconsin.

Over the last year the disease has been documented in wild birds in every state except Hawaii, as well as at commercial production facilities in the U.S. and abroad. Brazil recently declared an animal health emergency due to the virus.

California condor at risk

U.S. officials on May 16 announced the emergency use of a bird flu vaccine to protect the California condor, an endangered species that has already bounced back once from the brink of extinction.

After finding a California condor dead from bird flu in March, the U.S. Fish and Wildlife Service sought help from the USDA. Since then, at least 13 condors with bird flu have died, all near the Arizona-Utah border, according to the USDA.

The deaths have alarmed wildlife officials and come from a world population of California condors estimated at 561 at the end of 2022, including 347 free-flying birds in three western states and Mexico and 214 in captivity, according to the USFWS.

The vaccine must first be tested, however. Before it will be used on condors the wildlife service plans to conduct a pilot safety study on vultures, marking the first time the vaccine has been tested on wild birds in the U.S., said Joanna Gilkeson, a wildlife service spokesperson.

Bird flu also found in humans, other mammals

The disease has also shown up in humans and other mammals. The relatively few human cases involved people with extensive contact with domestic birds.

Among wildlife, the virus has been detected in raccoons, skunks, red foxes, possums, coyotes and grizzly bears, according to the USDA.

Three juvenile grizzlies in Montana were found sickly last fall and were euthanized due to their poor condition; all tested positive for H5N1. Veterinarians for Montana Fish Wildlife and Parks suspect the bears and other wild mammals get the virus after consuming infected birds. 

So far it has not been proven that mammals can spread the disease and the Centers for Disease Control and Prevention considers the risk to humans to be very low.

Precautions such as wearing gloves are recommended, though, when handling game birds. And health officials recommend people avoid contact with sick or dead wildlife. Even if an animal is not suspected to have died from a contagious disease, gloves should always be worn if it must be handled for disposal.