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In a Hopeful First, American Crows Survive West Nile Virus

close up of the head and shoulders of a crow
American Crow by Bryan Calk/Macaulay Library.

Cornell University has documented American Crows surviving the fatal West Nile virus disease for the first time ever.

In research published in May in the Journal of Avian Medicine and Surgery, scientists at Cornell’s Janet L. Swanson Wildlife Hospital documented the immune response of five crows from 2017 to 2018 that received treatment and were successfully released back into the wild. During their hospital stays the crows received supportive care, including fluid therapy, B-vitamin supplementation, and antiparasitic medication, among other treatments.

Prior to these recoveries, crows known to have contracted West Nile Virus had a 100% mortality rate.

“[Crows with West Nile virus] get very sick very quickly and shut down. They usually die within four days of being infected,” says Kevin J. McGowan, a scientist and crow expert at the Cornell Lab of Ornithology. “This is the first time any American Crow has survived [to my knowledge].”

McGowan is a course developer and instructor for the Cornell Lab’s Bird Academy, where he leads an online class entitled The Hidden Life of the American Crow. Over more than 30 years, he has studied, banded, and tracked more than 3,000 crows around Ithaca, New York.

“The number of crows dropping dead in 1999 was actually the reason that we knew there was some kind of new disease going on in the first place,” McGowan said. “[In Ithaca] we would get calls from locals all the time about sick and dead crows in their backyards.”

a crow with a purple wing tag and colored bands on its legs, used for field studies
Kevin McGowan has banded and studied more than 3,000 American Crows in the Ithaca, New York, area, since the 1990s. Photo by Kevin McGowan/Macaulay Library.

According to McGowan, over half of the local American Crow population around Ithaca succumbed to the disease during a wave in 2002 (when he accumulated over 35 dead crows in his freezer, all of which were banded birds from his study population). Another outbreak in 2012 again killed about half of the local Ithaca crows, he said. New York City notably lost almost 6,000 crows in just four months in 1999 when West Nile Virus first appeared in the United States.

More than 250 bird species are susceptible to West Nile virus, but it is deadliest to corvids and raptors—including jays, magpies, ravens, eagles, hawks, owls, and especially American Crows. There is a vaccine available for birds, but widespread vaccination of wild bird populations is not feasible. Instead, scientists hope the Cornell study proves that crows are capable of overcoming West Nile virus, and that wildlife rehabilitation might help local crow populations become more resistant to the virus.

“Their most important protection will be whatever maternal immunity the crows can pass to their offspring,” said lead author Cynthia Hopf-Dennis, a Cornell clinical assistant professor of zoological medicine. “My hope is that when we return crows to the wild after treatment and rehabilitation, they are able to contribute to a stronger population that is able to survive the virus and provide some level of protection to their offspring.”

According to McGowan, the recoveries could mean a new chapter for crows and West Nile virus.

“It’s been pure death for 20 years,” he said. “This is a sign of light and we’ll take it. We’re extremely happy to have these crows survive and be able to get back out there, fully recovered.”

Meher Bhatia’s work on this story as a student editorial assistant was made possible by the Cornell Lab of Ornithology Science Communications Fund, with support from Jay Branegan (Cornell ’72) and Stefania Pittaluga.

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American Kestrel by Blair Dudeck / Macaulay Library

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