While investigating peregrine falcon territories across Nevada—suspended by a rope on a cliff face or peering through a telescope focused on tiny rock alcoves—wildlife biologist Joe Barnes documented a disturbing trend: Half of the state’s peregrines have vanished.
“From 2023 to 2025, in 72 different (Nevada peregrine) territories, overall occupancy rate is down 51 percent,” said Barnes, who works for the U.S. Fish and Wildlife Service in Reno and has studied raptors for more than two decades. “Half of the population has blinked out; we’ve lost half of our breeding population. Even more so, at Lake Mead, which was the stronghold, it’s only 44 percent occupancy. And things are still declining.”
Peregrine falcons have been a wildlife conservation success story in the Silver State, across the U.S., and throughout the Northern Hemisphere. The birds faced extinction by the 1960s but recovered after the pesticide DDT was banned in 1972. Peregrines returned as a breeding species in Nevada in 1985, and by 1999, they were removed from the nation’s Endangered Species List.
Barnes began studying the birds in Southern Nevada in 2004, when there were just 10 known nesting territories in the state. Since then, he and his collaborators have identified 101 nesting territories, containing 202 individual birds. Today, Barnes said, fewer than half of those nesting pairs remain. The missing birds haven’t migrated—they are presumed dead, he said.
That’s because peregrines mate for life, and the nesting pairs stake out a specific territory, defending it against other falcons and predators. They may move their nests from season to season, but they stay within the bounds of their defensive space. If one adult bird dies, its place is usually taken by wandering single falcons called “floaters,” who join a territory’s surviving bird.
“It’s hard to keep tabs on the floaters,” Barnes said. “Those are the prospectors. They see a vacancy, and they jump in. But the numbers (of nesting birds) are lower year after year. That means that the floaters also are down. Normally, the ratio is one breeder for every three or four non-breeders. When a spot opens, they fill it. But we’ve lost much of our floater population, too.”
It’s a global phenomenon. Researchers across the U.S. and around the world are reporting similar drastic reductions in peregrine populations. No one knows why that’s happening, but Barnes and other researchers suspect an especially virulent strain of bird flu is the main culprit.
In 2015, when a different strain of bird flu appeared, peregrine populations also decreased the following year. Their numbers rebounded as the flu threat dissipated. In 2022, a new strain of especially lethal avian flu arrived—and is still killing birds.
“(In 2016), the birds got hit one year but made it through the single cycle,” Barnes said. “But the 2022 strain is still out there, persisting over multiple years. With the previous strain, they just had to ride it out. … This new strain is almost 100 percent lethal to peregrines, and they die within three days. There’s no developing immunity to this strain, at least so far.”
Peregrines probably get the virus by preying on infected waterfowl, he said; waterfowl usually make up more than half their diet. The hunters bring the disease back to their nests, and the whole falcon family dies within days.
In addition, Barnes suspects mercury pollution depresses the birds’ immune systems, making them more susceptible to the virus.
He scaled cliffs and collected scraps from peregrines’ meals from hundreds of nests. “We’ve tested the birds the falcons ate for mercury, and the aquatic birds have higher mercury loads,” Barnes said. “Terrestrial birds have lower levels. … In all, I’ve counted 117 species of prey. Peregrines will eat everything from a hummingbird up to a Canada goose.”
In 23 years of studying falcons and other raptors, Barnes has made several discoveries and come up with ways to streamline the surveys of the elusive peregrines, which nest in remote areas. His research has included:
- Finding peregrines nesting in the Nevada desert, some as far as 30 miles from water sources that researchers had thought were essential for survival. “But there are some nests in the Great Basin’s wide-open desert,” Barnes said. “There are no geese or ducks, so they prey on smaller birds, which have fewer calories that are essential to a species like peregrines. It’s a harder life, but that’s a paradigm shift which allows for a larger population. We don’t know exactly why, but it is now a known and acknowledged phenomenon that they are not just restricted to areas near water.”
- Determining that peregrine nests, shallow bowls of pebbles found in alcoves on scorching Nevada cliff faces, are about 15 degrees cooler than the surrounding rock. “The cliffs are amazingly hot,” Barnes said, “but temperature sensors show those cooler temperatures and higher humidity at the nest. Those little potholes on the sides of cliffs where they nest are microclimates, and the falcons’ young, those little butterballs, are hatched into that.”
- Surveying nests more efficiently. When Barnes started surveying falcon nests, he set up his spotting scope and waited for four hours in the hope of spying the birds. Now, he uses a brief recording of a peregrine’s cry to stir the pot. The falcons, thinking an interloper is nearby, soon make themselves known. “Some of these cliffs are 500 feet tall, so it’s easy to miss them,” he said. “But using the peregrine call boils down four hours of looking into 10 minutes. They hear another falcon’s voice, and they get keyed up.”
- Collecting samples for genetic studies that show Nevada’s peregrine population is descended from Southern Nevada birds whose descendants steadily worked their way northward. “All Nevada birds are inter-related,” Barnes said. An exception is the three nesting pairs around Lake Tahoe, which are presumably genetically linked to peregrines from California, he said.
Barnes, who previously worked for the Nevada Department of Wildlife and also studies ferruginous hawks and golden eagles, said Nevada’s golden eagle population also has been decimated.
“We had about 3,000 golden eagles in the state, and we lost about 300 of them by 2024,” Barnes said. The eagles mostly prey on rabbits and other small mammals, rather than birds, so avian flu isn’t suspected as the cause of that decline.
Because eagles and falcons are no longer considered endangered species, research funding is hard to come by, Barnes noted. His work “is done on a shoestring,” he said. He climbs cliffs on some weekends and pores over data at home to keep tabs on the state’s peregrines. He searches nooks and crannies in towering cliffs. He scans mountain ranges and ridges for a glimpse of the falcons, which can dive from the clouds at more than 200 mph to sink their barbed beaks and razor-like talons into their prey.
However, against avian flu, the powerful predator is defenseless.
“Hopefully this year, I’ll see if (their numbers) have plateaued and stabilized, or if their population is still in decline,” Barnes said. “Wildlife and nature are resilient if you give them a chance. That’s comforting. I don’t want to be the guy saying the sky is falling. I want to get the full picture, the full story, and not preach doom and gloom. My job is to get the data and try to shine a light on something.
“Nature fights its way back.”
To hear the cry of a peregrine falcon:
