Jul. 17—ANDERSON — Wildlife experts investigating an unknown illness that has killed hundreds of songbirds in Indiana and several other states remain puzzled about its cause.
As of Monday, the disease had killed 462 birds across 65 counties in Indiana since late May, with hundreds more in Ohio, Kentucky, Pennsylvania, Delaware, West Virginia, Virginia and Maryland believed to have died from it.
Ornithologists and experts at testing labs have ruled out several viral diseases, including avian influenza and the West Nile virus, as well as bacterial afflictions like salmonella and chlamydia. They agree that definitively determining a cause for the illness will likely take time.
"Disease diagnostics can be either very fast or very slow," said Allisyn Gillet, an ornithologist with the Indiana Department of Natural Resources. "It can take a very long time, especially if it's something novel and we haven't really seen anything like this before, so I can't really give a confident answer as to when this will be determined, if at all it will be determined."
Gillet said the possibility of multiple factors being connected with the spread of the disease — including possible interactions among several disease agents — complicates the investigation. She likened the process to trying to find a needle in a haystack, but not knowing what the needle looks like.
Experts say it's not uncommon for unexplained illnesses to flare up among certain wildlife populations. However, this outbreak has received considerable public attention in part because it affects several species that are regularly seen in backyards, including common grackles, blue jays, European starlings, robins and cardinals.
"There are natural illnesses and diseases that will move through different groups of wildlife from time to time," said Brad Bumgardner, executive director of the Indiana Audubon Society. "That's effectively what we saw with the West Nile virus five to 10 years ago."
Wildlife officials have recommended residents remove bird feeders and bird baths from their yards in an effort to eliminate gathering points for the birds — in effect, forcing them to socially distance.
"We took down our buffets last year (during the pandemic)," Bumgardner said. "Now we're basically doing the same thing for the birds."
Bumgardner said little is known about the illness as far as methods of contagion and its transmission, and the advice for feeder removal is "precautionary." He added that concern over birds being deprived of a food source is largely needless.
"Ninety-nine percent of birds that are nesting right now are feeding their young with insects and caterpillars," Bumgardner said. "Taking down (feeders) will have no long-term or even short-term harm for these birds, and that will likely be true even into the fall."
Notable symptoms that characterize the illness include swollen eyes with what experts describe as a crusty discharge so severe that it has blinded some of the animals. Other birds showed strange behaviors, including being unusually unafraid of people, stumbling around and acting particularly disoriented.
One theory about the illness holds that it's connected to the emergence of Brood X cicadas throughout the Midwest in the spring. But many experts see flaws in that idea.
"That's a great example of correlation and not causation," Bumgardner said. "If I see a lot of red cardinals in my neighborhood, and then I notice that there are a lot of yellow cars, did the cardinals cause that? These (events) are coincidental incidences that are not the cause for it."
Gillet agreed, noting that although the timing of cicada emergence and the illness outbreak matches up well, there have been no definitive links between the two events.
"Whether that's true is still up for grabs," she said. "We simply do not know. There have been no confirmed links between cicadas and the songbird disease, and I think that link is becoming a little weaker as time goes on because the disease is continuing; however, the peak of the cicadas has long been gone."
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