COLUMBIA, Mo. (AP) — At Rock Bridge Memorial State Park Thomas Bonnot carefully takes a few steps. He stops, takes a phone out of his pocket, plays the call of the Acadian flycatcher and listens.

His gray eyes attentively scan the dense canopies of maples and oaks. Somewhere off to the right, a robin chirps, "cheer up." Bonnot turns his head to look but immediately loses interest. It's not the characteristic "peet-sah" call of the bird he's looking for.

The Acadian flycatcher is a small, olive-colored bird with gray and white stripes on its wings. Over 4.5 million of them breed in the United States in spring and summer.

People can spot it in almost every park and forest across the Eastern Coast. It is considered to be among the species with the least concern for extinction by the International Union for Conservation of Nature.

But even something so common can disappear in a century, according to research published last July in Nature Climate Change. There, Bonnot, the leading author of the study, and his team modeled the breeding success or failure of thousands of individual nests across the Midwest over the next 90 years.

They found that if current warming trends remain, the Acadian flycatcher may face extinction by 2100 because its predators thrive in warmer temperatures.

"If we could see major impacts and people realize that even common species that we might take for granted are threatened by climate change..." said Bonnot, a researcher in the MU School of Natural Resources and a fellow with the Northeast Climate Adaptation Science Center, "...that would be something, you know. "That would catch attention."

It all began more than 20 years ago. Groups of graduate students, mostly under the guidance of MU professor Frank R. Thompson, one of the authors of the study, went to the Central Hardwoods ecoregion — a forest area that covers nearly 99 million acres — to study birds. In Missouri, Illinois and Arkansas, they went into the woods looking for nests. Whenever they found one, they took down a GPS point and marked a nearby tree.

"You don't want to put any flagging on the nest or around it 'cause that would just be a nice, big welcome sign for a predator," Bonnot told the Columbia Missourian . "'What's this flag? Oh, let's check it out. Oh, look, there is a nest!'"

Students would go back periodically to see if the nest was still there and if the birds were surviving. They would do these checks until the bird families raised fully fledged nestlings. And so it went.

Every two or three years, new groups of students came by, did their research and left their notes on whether the nest produced successful offspring and what the habitat around it was like. Young researchers described how many trees were in the area and what kind.

From weather stations next to the nests, they gathered precipitation and temperature. They collected more data on the Acadian flycatcher than any of the other bird species they studied.

In parallel, another group of researchers focused on the behavior of the birds' predators.

"They actually even had cameras on some of the nest to see: OK, if the nest was deprivated that means something came along and ate the eggs, and what was it?" Bonnot said.

It turned out that, for the most part, the flying animals fell prey to the slithering ones. W. Andrew Cox, another author of the study, looked at all of these analyses but focused on the temperature. He found the reptiles hunted more in warmer temperatures, leading to fewer nestlings growing to be fully fledged.

Bonnot looked to the future, creating computer simulations of individual nests across the region and modeling the success of each nest, day by day, over 90 years.

He focused only on Acadian flycatchers and examined three climate scenarios. The first two, mild and moderate, imply that humans will reduce the amount of carbon dioxide that goes into the air and take other action to limit global warming.

In these scenarios, the population of flycatchers decreases at first but begins re-establishing itself in the middle of the century and recovers by the end of it.

In the worst case scenario, the ratio of fully fledged nestlings to female birds irreversibly declines. By 2100, it drops from the current ratio of more than two nestlings per female bird to less than one.

"If the productivity drops that much, they will not be able to maintain the population," said John Besser, president of the Columbia Audubon Society.

In Rock Bridge Memorial State Park, Bonnot continues to look intently through binoculars, but he doesn't see any flycatchers.

"This is the perfect spot," he said. "You'll find them on the slopes leading down to the creeks, rivers and Rock Bridge happens to have a lot of that."

But as the birds settle down, the spring, full of aggressive calls and romantic songs, turns into quiet summer.

"This is the time of the year when they are focused on keeping a low profile, eating as much as they can," Besser said. "There is not much reason to do singing right now."

He often goes hiking to the Wild Haven Nature Area, and the Acadian flycatcher is one of the birds he always expects to hear or see.

"It's kind of like a friend that you can always count on being there," he said.

According to Bonnot and his team's research, in 100 years, there might be no "peet-sah" call anymore.

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Information from: Columbia Missourian, http://www.columbiamissourian.com