Illinois crows returning from the West Nile virus, an amazing link to human health

Illinois crows returning from the West Nile virus, an amazing link to human health


Some consider them to be pests or indicators of extinction. For others, it is a sign of good luck. For Pullman resident Phoebe Murtagh, the American raven is a delightful addition to Chicago’s favorite parks.

“I’ve found them curious since I learned that they can use tools and detect faces, and clever animals tend to be more attractive because you end up wondering what they think,” Murtagh, 26 said.

The Chicago native spends most of his time in the garden and enjoys watching large, black birds watching the treetops. But he does not remember seeing so many crows grow up.

“In the last five, 10 years, I see [crows] more than I can remember, ”said Murtagh, who studied environmental science at the college and volunteered at the Chicago Conservation Corps.

He wondered if the number of crows in the city had really increased.

It turns out they have. There are more crows in Illinois today than in the early 2000’s, when he was a child.

The Illinois crow population has undergone major changes over the past 20 years. And the reason is not necessarily what you can expect

It goes back to 2001, when scientists discovered two dead crows in Chicago who had been tested for West Nile virus.

Although most people suffer from only a minor ailment, the Western Nile can be devastating. Since its first discovery in the United States, more than seven million people have been infected.

It also reduced the number of Illinois crows, which have not yet recovered as much as they did in the 1990s.

But, by continuing to monitor the state’s birds, scientists have been able to learn more about how the West Nile virus spreads and how to control it. And changes in the number of birds can serve as a warning system for all viruses, not just the Western Nile.

Ravens are “one of the most endangered species in the world,” said Tara Beveroth, an Illinois aerospace and Natural History Researcher who was hired in 2004 to help explain why so many birds were dying.

Jen Mui / WBEZ Curious City

The Nile West is destroying the Illinois crow

In the late 1990s and early 2000s, Illinois was home to the largest gathering of American crows in the world. Each year, more than 300,000 ravens come down to the vicinity of Danville from around the Midwest to make their winter habitat near Lake Vermilion.

And they were not just in central Illinois.

Ravens are “one of the most endangered species in the world,” said Tara Beveroth, an Illinois aerospace and Natural History Researcher who was hired in 2004 to help explain why so many birds were dying.

Ravens are predators, so they thrive in cities like Chicago, where there are many trees and food scraps in the garbage, Beveroth said.

Then, the West Nile reached Illinois. The virus has been spreading in Africa and the Middle East for decades, but the problems that occurred in the United States in 1999 were even more serious for humans and birds.

By 2002, just one year after the West Nile virus was first detected in two Chicago crows, it was estimated that half of all Illinois crows had died from the virus, according to Beveroth.

“Previously, I thought it probably wouldn’t be a big deal because there are so many diseases that occur in birds,” said Michael Ward, a senior ornithologist at Illinois Natural History Research. “But I was wrong in many calculations with the West Nile.”

In 2002, ornithologists in Illinois were witnessing massive deaths – not just crows but also jay and robin. And the disease did not just beat the number of birds.

Why West Nile hit Illinois so much

In 2002 alone, more people became sick and died from West Nile in Illinois than anywhere else in the country.

Scientists have a few theories about why Illinois was so difficult.

The first is related to how viruses spread between birds. West Nile viruses live mainly on birds, and birds of different species can spread each other. There is a strong possibility that humans could capture the Western Nile directly from a plane. People get the virus from mosquitoes that have bitten infected birds.

And although crows are the species of animals that are most likely to get sick and die from the Western Nile, they are known as the peripheral host or “dead end”. The virus kills crows very quickly, which makes it difficult for West Nile to adapt and spread.

It is another bird, an American robin, known as the “best broadcaster” of the West Nile.

“We know that robins don’t die from it just like crows die,” Ward said. “And so, because they do not die, and every year they have more children who are infected with the West Nile virus, which maintains the viral cycle.”

By analyzing the blood in the mosquito’s intestines, scientists have also determined that mosquitoes prefer robin blood. Mosquitoes appear to eat more robin than other species, even though robin is not a common bird in the area, Ward said.

There are huge roosts of robins that return to Illinois every year. Because they are less likely to die from the virus, there is a greater chance of mosquitoes biting an infected robin and then biting a human and transmitting the virus.

Combining the Chicago mosquito population with a large number of excellent robin spreaders, and experts say you have recipes for high levels of infection.

But scientists like Ward said it was also possible Illinois did not have more Nile Western cases than other states but instead could have better data.

“We know [the virus] “It was very severe in the Chicagoland area, but we are also doing a lot of bird monitoring, so we may be more prepared to detect the effects,” he said.

Tara Beveroth, a bird psychologist with the Illinois Indigenous History Research, set the net in a 300-acre natural area owned by the University of Illinois. After a plane takes off in a net, scientists place a belt on its foot that allows it to monitor its movement and also to determine how many birds are in different locations and in what kind.

Claire Caulfield / WBEZ Curious City

Tracking crows

So why does Does Illinois have good data like this on crow numbers?

The process of counting crows is more complicated than you can imagine.

Illinois has been preserving the province’s natural resources for more than 160 years, but it was only in the 1970’s that a scientist named Vernon Kleen began hiring volunteers to count birds.

At the time, Kleen was struggling to gather accurate records of government airlines because different calculations used different methods.

Thus, in 1972, he recruited 650 volunteers in 62 counties for the first census of a state-of-the-art spring flight. Volunteers and scientists spread across the state to identify the different birds they see and hear. They have continued to do so every year since then.

Scientists at the University of Illinois use the data to estimate how many birds of all species there are in the state – and having 50 years of accurate data gives Illinois significant advantages in identifying styles.

“It’s really fun to partner with a lot of fun and interesting people who care about birds,” said Beveroth, who runs a spring and Ward flight count. “I’m so happy, I can’t sleep well last night.”

At this year’s count this weekend, he expected more than 1,000 volunteers to spend the day searching for flights in all 102 counties.

It is because of the data collected each year that scientists know the number of crows has increased dramatically in the last decade.

“They’re doing well,” Beveroth said.

Leta Chesser, a vector scientist at the University of Illinois, and laboratory assistant Noah Seo analyzes DNA from blood in the mosquito's intestines.  Understanding what mosquitoes prefer to bite helps scientists better understand how mosquito-borne diseases are.

Leta Chesser, a vector scientist at the University of Illinois, and laboratory assistant Noah Seo analyzes DNA from blood in the mosquito’s intestines. Understanding what mosquitoes prefer to bite helps scientists better understand how mosquito-borne diseases are.

Claire Caulfield / WBEZ Curious City

Why has the number of cases decreased?

Illinois has had mosquito control districts since 1927, when officials created them to deal with malaria outbreaks. Workers hunt areas where mosquitoes could lay eggs, kill tadpoles, and spray regularly.

In response to the West Nile, the city of Chicago increased its mosquito response, and mosquito control districts across the state saw an increase in membership.

That is one reason why scientists say the number of West Nile infections is declining – both in humans and in birds.

There are two theories about what else may have contributed to the decline.

It is possible that the virus has changed, Beveroth said. Scientists think these changes may lead to lower viral load, which means that there is less virus in the bird’s blood. This gives the bird a better chance of survival – and reduces the chances of mosquitoes transmitting the virus to humans.

There is a second theory as to why the number of infections has decreased in birds. Scientists know that crows have begun to develop antibodies, which means that their immune system is learning to fight off viruses.

Scientists continue to target and test mosquitoes for infectious diseases. There are more than 50 mosquito species in Illinois, with Chris Stone, director of the Illinois Natural History Survey’s medical entomology laboratory. Stone said each presents different challenges and possible health risks.

This year, the Stone team pays special attention to black-tailed mosquitoes. It can infect humans with the virus of Equine Eastern encephalitis, which can be even more dangerous than the Western Nile.

“It’s very rare, but it has been expanding geographically,” he said. “So we’re worried if it could happen sometime in Illinois because we’ve seen it in neighboring states like Indiana and Michigan and Wisconsin.”

Stone hopes the COVID-19 epidemic has helped Americans realize the importance of understanding and fighting the virus.

“It seems like a matter of time until the next big virus, and it could be a mosquito-borne virus,” he said. “Because of COVID, everyone has seen how easy it is for future viruses to come and how big those effects can be.”

Preventive measures, protect yourself

As with COVID, there are things you can do to protect yourself from the West Nile virus.

The first is to check your yard for standing water. Many species of mosquitoes lay their eggs in water, and they absorb only a small amount of water without interruption for the larvae to grow. Whether you put any tires, buckets, buckets, toys, ponds, bird baths, flower pots or trash cans out, cleaning them once a week during spring and summer can make a big difference.

In Illinois, the mosquito season lasts from mid-April to October, although it mainly infects humans in July and August. Wearing long sleeves and light colored pants can help prevent bites. Insecticide is also a good option, but it is important to check that the product is proven to repel insects and is safe for children.

And scientists recommend reporting any dead bird to your health department.

“The crow is a symbol of species,” Beveroth said. “The crow told us, ‘Look, there are these viruses that happen, and they can cause harm to humans.’ … It’s almost like an earlier warning. ”