As the songbird outbreak in the east fades, the cause remains unknown

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The mysterious outbreak that has caused widespread death and disease of songbirds in the eastern and midwestern United States, statewide feeder removal recommendations and public concern seem to have calmed down.

From late April through July, reports of disoriented and dead songbirds with puffy eyes proliferated in nearly a dozen states. Most of the accounts were about juvenile birds, especially American robins, blue jays, grackles, and starlings, common visitors to backyards and bird feeders. Sick birds have been officially documented in Virginia, Maryland, Delaware, New Jersey, Pennsylvania, West Virginia, Kentucky, Ohio, Indiana and the District of Columbia . Agencies in each of the states have recommended removing feeders and emptying birdbaths as a precaution against social spread.

Since September 10, all states have lifted these advisories. The last agencies to do so were the Ohio and Indiana Departments of Natural Resources. The change came in response to a sharp decrease in the number of reports of sick and dead birds. But even though the number of active cases is declining, the cause of the disease remains a mystery.

“We were wondering, you know, ‘are people going to have to stop feeding birds in the long term? »», Says David Curson, director of bird conservation at Audubon Mid-Atlantic. In Maryland, where Curson is based, he says the first cases appeared in late April, declined through July and had all but stopped by August. In Ohio and Indiana, the first reports of sick birds were from wildlife rehabilitators during the first week of June, but faded on a similar schedule.

At the height of the outbreak, state agencies opened up online reporting systems and were overwhelmed by reports of the disease from members of the public. “I think in the first week and a half we received 1,000 reports,” says Allisyn Gillet, the ornithologist with the Indiana Department of Natural Resources. Although many involved injuries and deaths of unrelated birds, she estimates that around 700 of the more than 4,300 reports in total have been confirmed as part of the outbreak. In Ohio, the situation was similar. Laura Kearns, a wildlife biologist for the state’s Division of Wildlife, says she ultimately believes as many as 1,000 of the thousands of total reports were of birds suffering from the same set of related symptoms. Pennsylvania was receiving hundreds of reports a day in early July, said Andrew Di Salvo, veterinarian for the state Game Commission.

Now all are saying that the tales of sick and dead birds have come down to a trickle in their respective states. And they attribute the few recent reports to other more standard explanations, like window collisions. Gillet adds that new reports have moved from Grackles, Jays and Robins to primarily finches, which are susceptible to House Finch eye disease, a type of conjunctivitis common at this time of year that can resemble the unidentified disease. .

Reports of the disease have remained low as feeders have risen, casting doubt on disease transmission between birds. But there are other variables at play, says Kearns. It is no longer the breeding and nesting season, which means that the vulnerable young birds hardest hit by the disease are either mature or dead. And it’s the start of the migration season, so the birds are on the move. Experts agree that it is difficult to say why the epidemic receded at that time and if there was a link with the feeders or the baths. “We’re in this curious position where this wave of disease has passed us, and people can start feeding their birds again, but we never really found out what it was,” Curson says.

The United States Geological Survey’s National Wildlife Health Center (NWHC) has been working with other partner institutions for months to identify a diagnosis, but they do not yet have a clear answer. Together, the group examined deceased birds and released a interagency statement, last updated on July 2. In the update, they shared what has been ruled out so far: Salmonella, Chlamydia, bird flu, Trichomonas parasites, West Nile, Newcastle disease, herpes and other viruses don’t were not detected in any of the birds. NWHC and its partners continue to investigate, test and stay in contact with affected states.

Meanwhile, biologists and wildlife managers across the state are divided over what they think are the most likely causes and are reluctant to speculate in the absence of clear evidence. Di Salvo points out that many potential culprits are still under investigation. “There are all kinds of things that could be out there, and honestly, we don’t know,” he says. But he is eagerly awaiting the results of the time-consuming metagenomic testing that NWHC and its partners are currently conducting. Metagenomics examines the entire bacterial community present within a cohort of sick songbirds and compares it to a control group to identify possible pathogens.

However, for tests like metagenomic screening to provide conclusive results, they require large numbers of bird samples, and with the end of the epidemic, these have become difficult to find, says Gillet. She adds that in the end, having fewer samples is a good thing. “Due to the nature of the disease and how it has presented itself so fleetingly, we may never get to the point where we have an answer,” she says. “And it’s good.” Her greatest hope is that the disease will not recur in the next breeding season.

To support long-term healthy bird populations, experts recommend staying vigilant about cleaning feeders, providing only fresh feed, removing feeders if you see sick birds, minimizing use pesticides and planting native plants. For now, however, birders can at least rest easy knowing this epidemic is over and they can finally welcome the birds to their feeders.

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