Some consider them pests and precursors of fate. For others, they are a sign of good luck. For Phoebe Murtagh, who lives in Pullman, American crows are a charismatic addition to her favorite Chicago park.
“They were intrigued because they knew they could recognize faces with tools. Clever animals are always the most interesting because they wonder what they are thinking. That’s what Murtagh, 26, said.
Lifelong Chicagoers spend a lot of time in the park and love to see big black birds exploring the tops of trees. But she doesn’t remember seeing many crows growing.
“In the last 5 or 10 years, [crows] Martag, who studied environmental science at university and volunteered for the Chicago Conservation Corps at the Chicago Academy of Sciences, said:
She wondered if the number of crows in the city was actually increasing.
I found out they have. Today Illinois has more crows than she did in the early 2000s when she was a kid.
Illinois crow populations have undergone dramatic changes over the last two decades.And the reason is not always what you expect
It dates back to 2001 when scientists discovered the dead bodies of two crows that tested positive for West Nile virus in Chicago.
Most people suffer from mild illness, but West Nile fever is fatal. More than 7 million people have been affected by the virus since it was first detected in the United States.
It also reduced the population of Illinois crows, but it has not yet recovered to the state of the 1990s.
But by keeping track of state birds, scientists could learn more about how the West Nile virus spreads and how it can be contained. Also, changes in bird populations serve as an early warning system for all types of viruses, not just West Nile fever.
Crows are “one of the most successful generalist species everywhere,” said Tara Bevelos, a bird ecologist at the Illinois Natural History Survey, who was hired to find out why so many birds died in 2004. I am saying.
Jen Mui / WBEZ Curious City
West Nile fever devastates crows in Illinois
From the late 1990s to the early 2000s, Illinois was home to the largest collection of American crows in the world. Each year, more than 300,000 crows come from around the Midwest to the north of Danville to make winter roosts near Lake Vermilion.
And they weren’t just in the heart of Illinois.
Crows are “one of the most successful generalist species everywhere,” said Tara Bevelos, a bird ecologist at the Illinois Natural History Survey, who was hired to find out why so many birds died in 2004. I am saying.
Crows are omnivorous, so they work very well in cities like Chicago, where there are lots of trees in the trash can and lots of food debris, Bevelos said.
Then West Nile fever arrived in Illinois. The virus has been epidemic in Africa and the Middle East for decades, but the strains that emerged in the United States in 1999 were deadly to both humans and birds.
According to Bevelos, it was estimated that half of the crows in Illinois had died from the virus by 2002, just one year after the West Nile virus was first detected in two Chicago crows.
Michael Ward, senior ornithologist at the Illinois Natural History Survey, said: “But I was wrong in several respects with West Nile fever.”
Throughout 2002, Illinois ornithologists witnessed the major deaths of jays as well as jays and robins. And the disease did more than just hit bird populations.
Why West Nile fever hit Illinois
In 2002 alone, West Nile fever in Illinois killed more people than anywhere else in the country.
Scientists have several theories as to why Illinois was particularly hit.
The first has to do with how the virus spreads among birds. West Nile virus is predominantly inhabited by birds, and different species of birds can spread to each other. Humans rarely catch the West Nile directly from birds. People get the virus from mosquitoes that bite infected birds.
Crows are the most likely animal species to get sick and die in the West Nile, but are known as peripheral or “dead end” hosts. The virus kills crows very quickly, making it really difficult for West Nile fever to mutate and spread.
Another bird known as the West Nile “super spreader” is the American Robin.
“We know that Robin never dies like a crow,” Ward said. “And because they don’t die, and every year, more and more babies are susceptible to West Nile virus, maintaining the virus cycle.”
Scientists also determined that mosquitoes prefer Robin’s blood by analyzing the blood in the mosquito’s stomach. Even if Robin isn’t the most common bird in the region, mosquitoes seem to eat more Robin than any other species, Ward said.
There is Robin’s big roost returning to Illinois every year. Because they are less likely to die from the virus, mosquitoes have more chances to bite the infected Robin and then bite humans to spread the virus.
Combining Chicago’s dense mosquito population with a large number of super-spreader robins, experts say you have a high rate of infection recipes.
However, scientists like Ward said that Illinois may not have actually had more cases of West Nile fever than other states, but instead have better data. May be.
“We know [the virus] It was particularly intense in the Chicagoland area, but with a lot of bird surveillance, it could have been ready to determine the impact, “he said.
Tara Beveroth, an avian ecologist at the Illinois Natural History Survey, has installed a mesh net in a 300-acre natural area owned by the University of Illinois. After the bird jumps into the net, scientists place a band on its paw so that its movement can be tracked. Also, determine how many birds are in different areas and what species they are.
Claire Colefield / WBEZ A curious city
Track crows
why To do Does Illinois have such good data on crow populations?
The process of counting counting crows is more complicated than you might think.
Illinois has held records of the state’s natural resources for over 160 years, but it wasn’t until the 1970s that a scientist named Vernon Clean began recruiting volunteers to count birds.
At the time, Kleen struggled to create accurate records of state bird populations, as different counts were used differently.
So, in 1972, he recruited 650 volunteers in 62 counties for the state’s first spring bird count. Volunteers and scientists spread throughout the state, focusing on the different birds they see and hear. Since then, they have been doing so every year.
Scientists at the University of Illinois use the data to estimate the number of different birds inhabiting the state. Having consistent data for 50 years gives Illinois a great advantage in determining trends.
“It’s really fun to work with many fun and entertaining people who care about birds,” said Bevelos, who runs the Spring Bird Count in the ward. “I’m so excited that I can’t sleep well the night before.”
In this weekend’s count, she expected more than 1,000 volunteers to spend the whole day searching for birds in all 102 counties.
It is thanks to the data collected each year that scientists know that crow populations have been steadily increasing over the last decade.
“They are doing well,” Bevelos said.
Leta Chesser, a vector science specialist at the University of Illinois, and Noah Seo, a lab assistant, analyze DNA from the blood of the mosquito’s stomach. Understanding which species mosquitoes prefer to chew helps scientists better understand how mosquito-borne diseases spread.
Claire Colefield / WBEZ A curious city
Why did the number of cases decrease?
Illinois has a mosquito control area since 1927, when authorities slaughtered mosquitoes in response to malaria outbreaks. Workers hunt down where mosquitoes can lay eggs, kill larvae, and spray pesticides on a regular basis.
In response to West Nile fever, the city of Chicago has increased mosquito response and membership has increased in mosquito control districts throughout the state.
This is one of the reasons scientists say the number of West Nile infections has decreased — for humans and birds.
There are two other theories about what might have contributed to the decline.
The virus may have mutated, Bevelos said. Scientists believe that this mutation can lead to a reduction in virus numbers. This means that there are few viruses in the blood of birds. This makes birds more likely to survive and less likely to cause mosquitoes to infect humans with the virus.
The second theory is why the number of bird infections has decreased. Scientists know that crows have begun developing antibodies. This means that their immune system is learning to fight the virus.
Scientists continue to capture and inspect mosquitoes for mosquito-borne diseases. Illinois is home to more than 50 species of mosquitoes, including Chris Stone, head of the Medical Entomology Laboratory of the Illinois Natural History Survey. Stone said each presents different challenges and potential health risks.
This year, Stone’s team is paying special attention to black-tailed mosquitoes. You can be infected with the Eastern Equine encephalitis virus, which is more dangerous than West Nile fever.
“It’s very rare, but it’s expanding its geographic range,” he said. “Therefore, as it was seen in neighboring states such as Indiana, Michigan, and Wisconsin, there is concern about whether it could pop up in Illinois someday.”
Stone hopes that the COVID-19 pandemic has helped Americans recognize the importance of understanding and fighting the virus.
“It seems like it’s only a matter of time before the next big virus arrives, and it may be a mosquito-borne virus,” he said. “Thanks to COVID, everyone has seen how easy it is for the next big virus to occur and how dramatic their effects are.”
Steps to delay spread and protect yourself
Like COVID, there are things you can do to protect yourself from the West Nile virus.
The first is to check if there is water in the garden. Many mosquito species lay eggs in water, and the larvae need a little unobstructed water to grow. If you keep your tires, buckets, planters, toys, pools, bird baths, flowerpots and trash cans outdoors, rinsing once a week in the spring and summer can make a big difference.
In Illinois, the mosquito season is from mid-April to October, but mainly in July and August. Wearing long sleeves and light-colored trousers will help prevent bites. Insect repellent is also a good option, but it is important to make sure that the product is insect repellent and has proven to be safe for children.
And scientists recommend reporting dead birds to your health department.
“The crow is an indicator species,” Beveroth said. “The crow told us,” Look, there’s this virus going on, and it can potentially harm people. “… It’s almost like a warning. “
