3556. How Wild Turkeys Took Over New England

By Briana Abbott, audubon.org, November 22, 2021

Photo: Kamran Nayeri

In suburban New England, gobbling gangs roam the streets. Wild Turkeys, each weighing in at 10 or 20 pounds, loiter in driveways, trapping residents inside their homes. They lounge on decks, damage gardens, and jump on the car hoods. Flocks of 20 or 30 birds roost in backyards, while particularly plucky turkeys chase down mailmen and the occasional police cruiser. They even fly (granted, not very well) across highways; one left a turkey-size dent in an ornithologist’s windshield. So far in 2018, the Massachusetts Division of Fisheries & Wildlife, or MassWildlife, has received 150 turkey-related calls and complaints, primarily from residents of densely populated counties in the southeast and Cape Cod. These are the Wild Turkeys of New England, and they’ve taken over.

The turkeys’ subjugation of New England residents is a relatively recent phenomenon. Just 50 years ago, the Wild Turkey population in New England was essentially non-existent, and had been for over a century. Then, an extensive, coordinated effort to trap and transfer turkeys across state lines rejuvenated the population—a comeback lauded by wildlife biologists and agencies as a conservation triumph. “It was an all-hands-on-deck restoration effort,” says Chris Bernier, a wildlife biologist at the Vermont Fish & Wildlife Department. “It’s a fabulous success story.” But now, with turkeys practically running the show, agencies must find a balance between celebrating the Wild Turkey revival and ensuring that human and bird get along. “We’re at opposite ends of the spectrum from where we were 50 years ago,” says wildlife biologist David Scarpitti, who leads the Turkey & Upland Game Project at MassWildlife. “It’s gone from a conservation success story to a wildlife-management situation.”

Before Europeans first colonized New England in the 17th century, an estimated 10 million Wild Turkeys stretched from southern Maine to Florida to the Rocky Mountains. As settlers spread out across the continent, they cut down forests as they went—and New England took the biggest hit. Forest area decreased 70 to 80 percent in Massachusetts alone in the first half of the 19th century, says Jim Cardoza, a retired wildlife biologist who led the Turkey & Upland Game Project at MassWildlife during the 1970s conservation effort.

As a result, the birds lost not only the cover of their habitat but also their food supply of acorns and chestnuts. Without hunting restrictions, hunters picked off any Wild Turkeys that survived the deforestation. By the mid-1850s, New England’s turkeys had all but disappeared. In the 1930s, biologists released hundreds of captive-bred turkeys into the region to try and resuscitate the species, but these domesticated birds couldn’t survive in the wild.

In the 1960s, biologists began to explore the idea of trapping Wild Turkeys, primarily from New York, and transporting them for release in New England. Biologists like Cardoza and his team sat in their trucks on cold winter mornings, sometimes for eight hours, waiting for Wild Turkeys to follow the trail of cracked corn, wheat, and oats to an open farmyard or pasture. Once 20 or so birds had gathered, Cardoza fired a 2,625-square-foot cannon-net towards the gaggle to capture them before tagging the birds for relocation.

Massachusetts captured 37 Wild Turkeys from New York’s Adirondacks in the 1970s and released them in the Berkshires. Vermont relocated 31 New York turkeys in the mid-1960s, and Connecticut, Maine, and New Hampshire participated in similar programs. By that time, the New England human population had migrated and condensed into cities, and forests and food had returned to much of the abandoned farmlands. Turkey predators like cougars and wolves had been extirpated, and the entire region created hunting restrictions to protect the birds. All the while, trapping and relocation continued between and within states—and soon New England’s Wild Turkeys, once considered extinct, were resurgent.

“Their population just exploded, quite literally,” Bernier says. Today, the Wild Turkey population in Massachusetts exceeds 25,000 birds. There are 45,000 Wild Turkeys in Vermont, 40,000 in New Hampshire, and almost 60,000 in Maine—almost all of which descended from those few dozen relocated birds, Bernier says. They now cover more terrain than they did before they disappeared; some Wild Turkeys even filled in pockets of previously uninhabited land on their own, something that researchers didn’t expect. “They did better than anybody thought that they would,” says Matthew DiBona, wildlife biologist with the National Wild Turkey Federation. The U.S. population is back up to roughly 6.2 million birds, he says.

In the mid-2000s, however, the turkeys started colliding with humans. New England is one of the most densely populated regions in the United States, and as people began putting out birdfeeders and growing gardens, turkeys found ample food. And the Wild Turkeys in suburbia, unlike skittish rural-roaming turkeys, quickly grew accustomed to humans. “No one had any idea that these birds would be showing up in suburbs,” says Marion Larson, the chief of information and education at MassWildlife. “There was no precedent for it.”

Overall, locals don’t mind the company. Some eager residents even go out of their way to attract the birds by scattering nuts, seeds, and berries on background platforms or intentionally growing nut-producing trees. But that warm welcome sometimes fades as the turkey-human scuffles continue to mount, and residents claim that the birds are a nuisance.

Encounters with the four-foot-tall turkeys can be dangerous, especially to a household pet or a small child. The birds can act aggressively towards humans by charging at them, pecking at them, or otherwise intimidating them. They also attack reflective surfaces that they mistake for other turkeys. That’s because the birds, usually male, are trying—and succeeding—to establish themselves at the top of the town’s pecking order. “This is the way they deal with socialization,” Larson says. “They’re treating people as if they’re turkeys.”

Outside of cities, Wild Turkey populations, such as in some southeastern and midwestern states, are on the decline as other forests are converted to farmland. But the urban birds continue to flourish in New England. Now wildlife agencies across the region are tasked with managing both the Wild Turkeys and their human neighbors to make sure encounters don’t go awry. The answer, biologists say, is simple: “We just need to stop feeding them,” Scarpitti says.

That’s what he tells local residents when he’s called to mediate neighborly disputes: Don’t feed the birds, and don’t show fear. But people hardly ever listen, and so for the foreseeable future, Wild Turkeys will continue to rule the neighborhoods of New England.

3546. Drought? This Is What Climate Change Looks like in the West

By Karyn Stockdale, Audubon.org, August 24, 2021 

Living back East for a few years, I missed the expansive bright blue skies of the Rockies. Now that I’ve returned to the West, I’m remembering the smoky haze that fills the sky. I’m remembering how the smell of summer has turned into the smell of smoke from wildfires. How the ash from fires hundreds of miles away sometimes coats your car and porch furniture. But it’s getting worse.

I’m used to the seasonality of streams—the spring runoff that slows to a trickle with hot summer days. My kids would wait for the monsoon storms to bring back the water flowing to our arroyo. But it was shocking to see how low the rivers and streams got so early this year. Recently, some southwestern states have seen abundant monsoonal rainfall, with some intense flooding. But in Utah, Nevada, California, and parts of the Northwest, the dryness and record-setting heat waves have intensified large wildfires. The combination of drought and heatwaves are pushing birds to their limits, leading to lethal dehydration.

Welcome drought.

There's a lot to unpack in that word. Decades of drought in the West seems to be hitting a tipping point, garnering national attention. More and more, people are recognizing this isn’t just a drought. This isn’t temporary.

It’s fires, it’s decreasing water supplies, it’s air quality issues, it’s high temperatures, and unpredictable weather. It’s an era of extremes.

This summer has turned into the worst water year for many farmers and ranchers, for wildlife managers, for businesses and communities concerned about their water supplies. We urgently need to adapt and better prepare for constant drought and for extremes to become more common. As my colleague said recently, “This is climate change stealing your water.”

Climate change is increasingly impacting all of us—threatening the health of millions of birds, our food supplies and economies, our air quality, and the water security for all of us. It’s starting to affect our way of life.

And this affects birds. The future of several bird species, including some protected by the Endangered Species Act, is tied to the health of rivers and lakes. We’ve already lost too many wetlands and riparian habitats across the West and birds are pushed to congregate in high concentrations in the last places left with water. You might recall the death of 40,000 ducks from avian botulism last year due to overcrowded conditions with limited water and habitat left at the Lower Klamath National Wildlife Refuge.  

How bad is this drought? 2021 is shaping up to be the driest year in the last century.

Everywhere in the West we see signs of the ongoing megadrought. Here are a few indicators that we are concerned about at Audubon:

• Lake Mead, the largest reservoir on the Colorado River (and in the country), has officially reached its lowest water level in history—and it’s expected to continue dropping.
   
• Great Salt Lake reached its lowest lake level ever recorded, and will continue to drop this year, maybe even by a foot more.
   
• Years of reduced inflows, along with drought and a warming climate, continue to shrink the Salton Sea in California, impacting the health of surrounding communities and the available habitat and food sources for migratory birds.
   
• Our last remaining wetlands in California’s Central Valley—essential Pacific Flyway habitat for waterfowl—are expected to receive only about 57% of their water supply.
   
• In rural Arizona, unlimited groundwater pumping (80% of the state has no groundwater management!) is causing wells to go dry and further stressing flows in rivers and streams.
   
• The Klamath River Basin’s drought is testing everything:  There's not enough water to meet all the demands from farmers, tribes, and wildlife, including endangered fish.
   
• The Southwest’s other major river basin—the Rio Grande—is also historically dry.

At Great Salt Lake, the 17 named islands that usually exist on the lake, where nesting birds are protected from predators, are now peninsulas. In this “Year of the Shorebird” as designated by Utah’s Governor, the decreased water coming into the shrinking lake is affecting the whole ecosystem with potentially hemispheric implications. Great Salt Lake and its surrounding wetlands create vital habitat in the Western Hemisphere for millions of breeding and migrating shorebirds including more than 56% of the global population of American Avocets and nearly 30% of the global population of Wilson’s Phalaropes. If nothing is done to reverse course, Great Salt Lake risks suffering the fate of other large, saline lakes around the world, the loss of which invariably triggers dramatic harm to communities, local business, and human health.

In the West, we are used to competing demands for scarce water for farms, cities and rural communities, hydropower, recreation, and the environment (typically last in consideration) which can lead to conflict. Audubon’s Western Water team continues to push for all of us to face these risks and plan for water shortages with a changing climate in mind.

I keep thinking of that folk song “It Ain’t Gonna Rain No More” from my childhood. My extended family lived through the Dust Bowl in Texas and Oklahoma and went into dryland ranching. This year doesn’t feel like business as usual—it feels like the cusp of another Dust Bowl.

New approaches are needed to adapt to, respond to, and mitigate the compounding and extreme risks of climate change to communities, economies, ecosystems, and the water resources that support them.

This is why Audubon is working in state capitals and in Washington, D.C. to advocate for sensible policies and funding that benefit birds and communities alike. We have worked to ensure that the needs of birds and habitat aren’t carved out of policy decisions and water management.

Audubon is also working to secure water to enhance habitats where water is most needed. Working with partners, we continue to enable and secure water flows in rivers in places like Colorado, New Mexico, Utah, California, and Arizona. And through our science, we are improving our understanding of the long-term health of priority places for birds and how we might better manage the limited water availability into the future. 

With drought conditions persisting now into a third decade and climate change increasingly impacting water supplies and habitat in the West, we urgently need inclusive and equitable long-lasting water solutions for climate resilience. Please join us in advocating for policies, funding, and on-the-ground actions that result in sustainable change.

3535. This ‘Shazam’ for Birds Could Help Save Them

By Margaret Renkl, The New York Times, July 26, 2021 

Northern Cardinal

I spent my entire childhood playing in the woods and meadows of rural Alabama. The world back then was lush and green: cooled by creeks, carpeted by pine needles, attended by birdsong. In those days there were nearly three billion more birds in North America than there are today, and my young days played out beneath the sound of their music.

The staggering loss of birds — nearly a third of them since 1970 — is due to human behavior: to climate change, to deforestation and ecosystem fragmentation, to insecticides and free-roaming pets, to light pollution in our skies and microplastics in our waterways, to glass-encased skyscrapers protruding into migratory flyways, among other choices that favor our own convenience over the lives of our wild neighbors.

I can’t help but wonder how much of the blame lies, too, in indifference, our failure even to notice what we’ve lost. Birds can be secretive creatures, staying high in the treetops or deep in the underbrush. Even those in plain sight often move startlingly quickly, appearing as hardly more than a flash of color, a blur of wings. Except for the background sound of birdsong, many people are never aware of how many birds — or how few — they share the world with.

Apps like iNaturalist from National Geographic and the California Academy of Sciences help to close that gap, functioning as both electronic field guides and vast data-collection devices. They learn as we learn, improving with every photo and map pin we upload, helping experts understand a planet undergoing profound change. But what of the vast number of birds we never see, those we only hear? To offer that feature — one that accurately and consistently recognizes birds by sound alone — would be the birding equivalent of finding the Holy Grail.

Identifying birds by their songs has always been difficult, for computers and humans alike. Every species of bird has a range of vocalizations, sometimes an immense range, and those vocalizations can have regional inflections, just as people speak with local accents. In some species, individual birds put a unique spin on their songs, too. A mockingbird is the avian equivalent of a jazz musician.

Last month, the Cornell Lab of Ornithology released an updated version of its Merlin Bird ID app, which allows users to identify birds by song. There are other voice-recognition apps for birds, but they are accurate barely 50 percent of the time. Though Merlin doesn’t claim to be 100 percent accurate, it comes very close. Drawing on a database of notes and recordings contributed by tens of thousands of citizen scientists through the Lab’s eBird initiative, Merlin listens as you listen, in real time, and tells you what you’re hearing. The app can identify some 400 North American species so far and will keep expanding. It’s an immense achievement, a quantum leap forward, nothing less than “a Shazam for bird songs,” as an article in Fast Company put it. 

Naturally, I had to try out the new technology. I am far from an expert birder, but I do know my avian neighbors, and I figured a good way to test Merlin’s accuracy was to try it with birds I can already recognize by ear.

The first test didn’t bode well. I was reading on the sofa when I heard a Carolina wren singing just above my head. It was hopping around in a hanging basket barely a foot beyond the glass and singing its head off. That wren was as close as any bird was ever going to get, but the app was stumped. “Merlin has no matches,” it reported. Merlin fared no better in the two other recordings I made indoors.

But outside, something magical happened. I set my phone down on the table on my back deck, opened the Merlin app, chose “Sound ID” and hit the microphone button. Immediately a spectrogram of sound waves began to scroll across the screen. Every time a bird sings, the sound registers as a kind of picture of the song. By comparing that picture with others in its database, the app arrives at an ID.

I watched as Merlin rolled out the names of bird after bird — tufted titmouse, European starling, Carolina chickadee, northern cardinal, American crow, white-breasted nuthatch, eastern towhee, house wren, American goldfinch, blue jay, eastern bluebird, American robin, Carolina wren, house finch. It didn’t miss a single one.

What amazed me was not merely the accuracy of the ID but also the way the app untangled the layers of song, correctly identifying the birds that were singing in my yard, as well the birds that were singing next door and the birds that were singing across the street. If the same bird sang a second time, the app highlighted the name it had already listed. Watching those highlights play across the growing list of birds was almost like watching fingers fly across a piano keyboard.

Then I started seeing the names of birds I’d never seen in this yard before, birds that for me have existed only as undifferentiated sounds in the trees: Kentucky warbler, blue-gray gnatcatcher, yellow-breasted chat. The new bird I’d been hearing but not seeing all summer long, the one whose song sounded to me like, “Here, here, do you know my name?” turned out to be a magnificent summer tanager. Merlin also picked up the song of a yellow-throated warbler, a bird the app identified as uncommon for this area. I knew two were here because one of their babies fell out of a nest onto my son’s car — it was safely reared by the wildlife experts at Walden’s Puddle and released back into the wild — but I had never heard them sing. At least, I didn’t know what I was hearing when I heard them sing.

This enchanting app is aptly named. Watching those birds appear on my phone screen in response to the sound of their voices in the air was a kind of wizardry — like watching the notes of a song become visible, like having fairies or angels suddenly embodied before me. Merlin made me see what before I could only imagine.

The timing for this app is perfect. During the pandemic quarantines, many people took up bird-watching as a pastime, and people who notice birds almost invariably become people who love birds. Love can’t save the environment, of course, but when enough voters fall in love, they can surely shift the political winds toward preservation.

That’s because we are a species motivated by love. Our most powerful work is done in the fervor of love; our most urgent effort is born from the fear of losing what we love best. To save birds, we need to make the whole human race fall in love with birds. What if all the people with phones in their pockets could suddenly hear beyond the sounds of their own machines? What if we could all discover how surrounded we are by bright-winged fairies and golden-voiced angels come down to live among us?

Thanks to the Cornell Lab of Ornithology, now we can.

3299. The Quiet Disappearance of Birds in North America

By Ed Yong, The Atlantic, September 19, 2019

In the early afternoon of September 1, 1914, Martha the passenger pigeon, the last of her kind in the world, passed away, and her entire species disappeared with her. But before that instant of extinction, there had been decades of decline, as hunters killed what was once the most common bird in the world. Billions of passenger pigeons became millions, thousands, and then hundreds, until eventually one became none. Few people took note of this decline as it happened: There still seemed to be a lot of pigeons, and their abundance obscured their downfall.

History is now repeating itself—across the entire avian world.

A new study, which analyzed decades of data on North American birds, estimates that the continent’s bird populations have fallen by 29 percent since 1970. That’s almost 3 billion fewer individuals than there used to be, five decades ago. “It’s a staggering result,” says Kenneth Rosenberg from Cornell University and the American Bird Conservancy, who led the analysis.

“This is a critically important study,” says Nicole Michel, an ecologist at the National Audubon Society. Past work has shown that specific groups of birds are declining, but this is the first study to rigorously put a number on the full extent of these losses. And surprisingly, it shows that the most ubiquitous birds have been the hardest hit. “The common wisdom was that we’d see the rare and threatened species disappearing and the common, human-adapted ones taking over,” Rosenberg says. Instead, his team found that 90 percent of the missing birds came from just 12 families, and that they were all familiar, perchy, cheepy things such as sparrows, warblers, blackbirds, finches, larks, starlings, and swallows.

About 19 species have each lost more than 50 million individuals. Seemingly ubiquitous species such as the red-winged blackbird are at risk. The dark-eyed junco, a type of sparrow and one of the most common sights at bird feeders, is in trouble. Even birds that humans successfully introduced to this continent—such as the house sparrow and European starling, which are famed for their adaptability—are in trouble. “If we can’t even keep introduced species in healthy populations, that could be a stronger indicator that the environment is unhealthy,” Rosenberg says. It’s as if all birds are canaries, and the entire world their coal mine.

As with the passenger pigeon, abundance obscures decline. The fact that 24 million eastern meadowlarks still survive hides the fact that 74 million have gone. “There are still a lot of birds out there,” Rosenberg says. “If you have a lot of birds coming to your feeder and they’re reduced by 30 percent, you might not see that. This loss of abundance can be happening right under our noses.”

With this great emptying of the skies, there are now 3 billion fewer beaks to snap up insects, and 3 billion fewer pairs of wings for moving nutrients, pollen, and seeds through the world. We haven’t just lost birds, but all the things that birds do, “as well as our connection to what is arguably one of the most widely cherished forms of wildlife on the planet,” says Kristen Ruegg from Colorado State University. “Our forests and backyards will continue to grow quieter with every passing year, and within that leftover space there is an opportunity for complacency about the natural world to grow.”

A broader pattern of “biological annihilation” is coming into focus, too. A third of backboned species on land, for example, are also declining, including many that are deemed by the International Union for Conservation of Nature to be of “least concern.” Insects might also be in trouble, although fears of an insect apocalypse are hard to judge because there’s very little long-term data on insect populations.

The opposite is true for birds, which are conspicuous, beloved, and heavily watched by both amateur enthusiasts and professional researchers. There’s long-term survey data aplenty, and Rosenberg’s team collected as much as it could for 529 species, covering most major groups. “The data sets they used provide probably the best long-term, large-scale information on species abundances for any group of organisms anywhere in the world,” says Natalie Wright from Kenyon College. “There’s always uncertainty. But if they are wrong, they are likely underestimating the magnitude of population declines.”

Rosenberg’s team also used data from a weather-radar network to show that the number of birds migrating through America’s nighttime skies has fallen by 14 percent since 2007. That’s important. The radar not only provides another line of evidence, independent of the more traditional surveys, but picks up species that those surveys miss, such as Arctic-breeding shorebirds. It “increases our confidence that these declines are really happening,” Michel says.

The new study is silent on the causes of these declines—that’s what Rosenberg’s team will look at next. But it’s widely accepted that “habitat loss and degradation are the largest forces behind the decline of birds,” Rosenberg says. The fact that grassland birds have suffered more than those in other habitats attests to this problem. As wild prairie has been converted into agricultural land, invaded by non-native plants, and flooded with harmful pesticides, 700 million local birds have disappeared, and three-quarters of bird species are going downhill.

It’s hard to estimate exactly how many birds are dying due to habitat loss, or from other potential dangers such as pesticide use, the disappearance of insect prey, or climate change. Other threats are easier to quantify, and the biggest of these, by some margin, is domestic cats, which kill an estimated 2.4 billion birds every year. Window collisions claim 600 million bird lives a year, vehicles take out 214 million, power lines are responsible for killing 32 million, and the lights of industrial towers fatally distract about 6 million. Wind turbines are often cited as a problem for birds, and while they should be placed carefully to protect migratory species, their effect is comparatively small; for every bird killed by a wind turbine, thousands are killed by a cat.

“Being able to tie any one of these drivers to the decline of a particular species or group is difficult,” Rosenberg says. “Cumulatively, they’re all important.”

The organizations behind the new study have compiled a list of seven personal actions that people can take to protect North America’s remaining birds:

1) Make windows safer with products that prevent collisions.

2) Keep cats indoors (or walk them on a leash).

3) Choose native plants instead of lawns, to offer food and resting places for migrants.

4) Avoid pesticides.

5) Choose bird-friendly, shade-grown coffee that’s grown on farms that preserve bird habitat.

6) Reduce the use of plastics, and especially single-use plastics.

7) Watch birds and report what you see to help scientists track the surviving populations.

Ultimately, it will take political will and action to refill the emptied skies—and there’s precedent for such reversals of fate. The number of raptors (hawks, eagles, and their kin) has doubled since the 1970s, thanks to a ban on the pesticide DDT and hunting restrictions imposed by the Endangered Species Act. At the same time, waterfowl such as ducks and geese have increased in number by 56 percent, after hunters lobbied for legislation to protect wetland areas. These success stories show that “when people band together and take action, it is possible to reverse population declines and bring species back from the brink,” Michel says. “Birds are down, but they’re not out. When you give them half a chance, they can recover.”

But Donald Trump’s administration has recently moved to gut the most important bird-conservation law in the United States: the century-old Migratory Bird Treaty Act. This proposal would absolve companies of responsibility for millions of incidental bird deaths, and hold them accountable only for purposeful killings, which are negligible. “This is the absolute worst time to be weakening protections,” Rosenberg says.

No one hunts the sparrow, he notes, but bird lovers are so numerous that they could form a constituency to match the political clout the hunting lobby used to save waterfowl. “We need to raise our voices,” Rosenberg says.

3283. Birds Are Vanishing From North America

By Carl Zimmer, The New York Times, September 19, 2019

Three billion birds

A survey of 529 bird species in the United States and Canada found that bird populations have fallen by 29 percent since 1970, a loss of nearly three billion birds.

Bird population change since 1970 by breeding habitat

–50%

–40

–30

–20

–10

0

+10

+20%

Grasslands

Boreal forests

Western forests

Tundra

Generalist

Tundra

Forest generalist

Eastern forests

Arid lands

Western

forests

Coasts

Wetlands

Boreal forests

0

Arid

lands

200 million

Grasslands

Eastern

forests

400 million

Note: Wetland and

coastal habitats

are not shown.

Habitat boundaries

are approximate.

Net loss of

600 million birds

1970

’80

’90

2000

’10

By The New York Times | Source: Science

The skies are emptying out.

The number of birds in the United States and Canada has fallen by 29 percent since 1970, scientists reported on Thursday. There are 2.9 billion fewer birds taking wing now than there were 50 years ago.

The analysis, published in the journal Science, is the most exhaustive and ambitious attempt yet to learn what is happening to avian populations. The results have shocked researchers and conservation organizations.

In a statement on Thursday, David Yarnold, president and chief executive of the National Audubon Society, called the findings “a full-blown crisis.”

Experts have long known that some bird species have become vulnerable to extinction. But the new study, based on a broad survey of more than 500 species, reveals steep losses even among such traditionally abundant birds as robins and sparrows.

There are likely many causes, the most important of which include habitat loss and wider use of pesticides. “Silent Spring,” Rachel Carson’s prophetic book in 1962 about the harms caused by pesticides, takes its title from the unnatural quiet settling on a world that has lost its birds:

“On the mornings that had once throbbed with the dawn chorus of robins, catbirds, doves, jays, wrens, and scores of other bird voices, there was now no sound.”

Kevin Gaston, a conservation biologist at the University of Exeter, said that new findings signal something larger at work: “This is the loss of nature.”

For decades, professional ornithologists have been assisted by an army of devoted amateur bird-watchers who submit their observations to databases and help carry out surveys of bird populations each year.

In the new study, the researchers turned to those surveys to estimate the populations of 529 species between 2006 and 2015.

Those estimates include 76 percent of all bird species in the United States and Canada, but represent almost the entire population of birds. (The species for which there weren’t enough data to make firm estimates occur only in small numbers.)

The researchers then used bird-watching records to estimate the population of each species since 1970, the earliest year for which there is solid data.

“This approach of combining population abundance estimates across all species and looking for an overall trend is really unprecedented,” said Scott Loss, a conservation biologist at Oklahoma State University who was part of the new study.

While some species grew, the researchers found, the majority declined — often by huge numbers.

“We were stunned by the result — it’s just staggering,” said Kenneth V. Rosenberg, a conservation scientist at Cornell University and the American Bird Conservancy, and the lead author of the new study.

“It’s not just these highly threatened birds that we’re afraid are going to go on the endangered species list,” he said. “It’s across the board.”

Weather radar offered another way to track bird populations. Dr. Rosenberg and his colleagues counted birds recorded on radar at 143 stations across the United States from 2007 to 2018. They focused on springtime scans, when birds were migrating in great numbers.

The team measured a 14 percent decline during that period, consistent with the drop recorded in the bird-watching records.

“If we have two data sets showing the same thing, it’s a home run,” said Nicole Michel, a senior quantitative ecologist at the Audubon Society who was not involved in the study.

Among the worst-hit groups were warblers, with a population that dropped by 617 million. There are 440 million fewer blackbirds than there once were.

Three Billion Birds

A survey of 529 bird species in the United States and Canada found that bird populations have fallen by 29 percent since 1970, a loss of nearly three billion birds.

Dr. Rosenberg said he was surprised by how widespread the population drop was. Even starlings — a species that became a fast-breeding pest after its introduction to the United States in 1890 — have dwindled by 83 million birds, a 49 percent decline.

Europe is experiencing a similar loss of birds, also among common species, said Dr. Gaston, of the University of Exeter. “The numbers are broadly comparable,” he said.

The new study was not designed to determine why birds are disappearing, but the results — as well as earlier research — point to some likely culprits, Dr. Rosenberg said.

Grassland species have suffered the biggest declines by far, having lost 717 million birds. These birds have probably been decimated by modern agriculture and development.

“Every field that’s plowed under, and every wetland area that’s drained, you lose the birds in that area,” Dr. Rosenberg said.

In addition to habitat loss, pesticides may have taken a toll. A study published last week, for example, found that pesticides called neonicotinoids make it harder for birds to put on weight needed for migration, delaying their travel.

The researchers found some positive signs. Bald eagles are thriving, for example, and falcon populations have grown by 33 percent. Waterfowl are on the upswing.

For the most part, there’s little mystery about how these happy exceptions came to be. Many recovering bird species were nearly wiped out in the last century by pesticides, hunting and other pressures. Conservation measures allowed them to bounce back.

“In those cases, we knew what the causes were and we acted on that,” Dr. Rosenberg said. “They’re models of success.”

But some thriving populations are harder to explain.

Tiny warbler-like birds called vireos are booming, with 89 million more birds than in 1970 — a jump of 53 percent. Yet warblers, which share the same habitats as vireos, have suffered a 37 percent decline.

“I have no idea why vireos are doing well,” Dr. Rosenberg said. “I’d love to do a study of vireos and discover what their secret is.”

The sheer scale of the bird decline meant that stopping it would require immense effort, said Dr. Young, of the University of California, Santa Barbara. Habitats must be defended, chemicals restricted, buildings redesigned. “We’re overusing the world, so it’s affecting everything,” she said.

udubon Society is calling for protection of bird-rich habitats, such as the Great Lakes and the Colorado River Basin, as well as for upholding the Migratory Bird Treaty Act, which the Trump Administration is trying to roll back.

The society and other bird advocacy groups also suggest things that individuals can do. They urge keeping cats inside, so they don’t kill smaller birds. Vast numbers of birds die each year after flying into windows; there are ways to make the glass more visible to them.

To some birders, the study’s findings confirmed a dreaded hunch.

Beverly Gyllenhaal, 62, a retired cookbook author, and her husband, Anders, have spotted 256 species in parks in the eastern United States. But when she visited her mother in North Carolina in recent years, it seemed there weren’t as many birds as she recalled from her childhood there.

And when she talks to people around the United States on her birding travels, many say the same thing. “Oftentimes people will tell you, ‘It’s nothing like it used to be,’” she said.

The estimated losses have left her appalled. “If the cardinals and the blue jays and the sparrows aren’t doing well,” she said, “that’s really scary.”