Artwork: Chris Maynard

Science

North America Has Lost More Than 1 in 4 Birds in Last 50 Years, New Study Says

For the first time, researchers have estimated the volume of total avian loss in the Western Hemisphere—and it’s not just threatened species that are declining. Many backyard favorites are also losing ground.

Almost anywhere you go, you can find birds. They scurry through the waves on every beach, sing as they wing over every prairie, raise chicks in nests in every wood, and visit every backyard. But while birds remain everywhere, people are actually seeing far fewer of them than just 50 years ago, according to a new study. It estimates that North America is home to nearly three billion fewer birds today compared to 1970—that’s more than 1 in 4 birds that have disappeared from the landscape in a mere half a century. 

“This was an astounding result, even to us,” says lead author and Cornell Lab of Ornithology conservation scientist Ken Rosenberg. 

The study, published today in the journal Science, marks the first time experts have tried to estimate sheer numbers of avian losses in the Western Hemisphere. Typically, conservation studies focus on a specific species, habitat, region, or type of threat. By taking a higher-level view, the study highlights that many birds we still consider common, ranging from Baltimore Orioles to Dark-eyed Juncos to Barn Swallows, are actually posting heavy population losses over time. 

Altogether, the research team—which included collaborators at the American Bird Conservancy, Smithsonian Conservation Biology Institute, U.S. Geological Survey, the Canadian Wildlife Service, and other institutions—analyzed the breeding population of 529 species by pooling data from the North American Breeding Bird Survey, Audubon’s Christmas Bird Count, U.S. Fish and Wildlife Service waterfowl surveys, and 10 other datasets. They also analyzed more recent data collected by weather radar technology that can track large groups of birds as they migrate to estimate their numbers.  

The weather radars indicated a 14 percent decrease in nocturnal spring-migrating birds in the last decade alone, helping the authors to verify the longer-term survey trends—especially for those breeding in remote northern habitats that aren’t as well monitored. Using models that incorporated all the data, they estimated the net number of birds lost over time, across various habitats and bird groupings. 

Bringing so many different datasets together is tricky work, says Nicole Michel, senior quantitative ecologist at the National Audubon Society, who was not an author of the study but provided some underlying data. The authors had to account for differences in collection methods, location, species elusiveness, and even the attentiveness of the data collectors themselves. Even with this detailed approach, the study didn't capture every North American species, and declines of each individual species included have varying uncertainty ranges, based on data available. Sea and shorebird data proved particularly limited, says Rosenberg, and many elusive birds had to be left out entirely.

Despite these gaps, the overall picture is clear, especially because the radar and survey data tell the same story of losses, Michel says. “Unfortunately for the birds, I think we can be very confident in these results,” she says. Scott Loss, an Oklahoma State University ecologist not directly involved in the study, agreed: “We know birds are in decline, but this is a really sobering picture of that decline," he says.  

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Tap the graphic below to see how the relative number of birds in each breeding habitat changed from 1970 to 2017. The colors indicate the percentage of decline (Red >30%; Orange <30%) or gain (Blue).

Click the graphic above to see how the relative number of birds in each breeding habitat changed from 1970 to 2017. The colors indicate the percentage of decline (Red >30%; Orange <30%) or gain (Blue)The size of each circle represents the relative abundance of birds per habitat type. 

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As expected, the study showed that birds that breed in at-risk habitats such as grasslands and the Arctic tundra are declining drastically. Grasslands in particular posted the biggest losses, with more than 700 million breeding individuals lost across 31 species since 1970, a more than 50 percent decline (see habitat breakdown below).

Far more surprising were far-reaching declines across habitats and bird types, says Michel. About 90 percent of the missing birds came from 12 distinct and widespread bird families, including warblers, sparrows, blackbirds, and finches. Common birds found in many different habitats—even introduced, ubiquitous species like European Starlings—experienced some of the steepest drops. Feeder birds like the Dark-eyed Junco declined by nearly 170 million individuals, the study's models estimated, while White-throated Sparrows dropped by more than 90 million.

There isn’t one single factor that can account for these pervasive losses, says Rosenberg. Habitat loss is likely an important driver in some biomes, but can’t explain the widespread declines on its own, says Arvind Panjabi, avian conservation scientist at Bird Conservancy of the Rockies and a study co-author. Multiple, complex environmental factors including pesticide use, insect declines, and climate change, as well as direct threats like outdoor cats and glass skyscrapers, are also hitting birds from a range of angles. For migratory species, long journeys and changes to winter habitats could pose additional challenges. The study itself doesn’t look at causes, but the results point to how human influence over the last 50 years has chipped away at bird populations, says Michel. 

“My hope is that this will spawn a greater awareness that we really need to take care of our environment,” Panjabi says. “In order to prevent another third of our birds disappearing before too long, we need to change how we do things.” Kevin Gaston, an ecologist at the University of Exeter not involved in the work, said such a possibility should concern everyone: "We’re undermining the role that these organisms have in structuring landscapes, in providing ecosystem goods and services and benefits," he says.

But while the results are troubling, there is some good news. Not all birds declined and some species even showed steady gains over time. Waterfowl as a group, for example, saw a population increase of 34 million individuals since 1970, thanks largely to wetland conservation efforts. Raptors, such as the Bald Eagle, also fared better with a gain of 15 million individuals thanks largely to a ban on DDT in 1972. The numbers show that taking steps like wildlife management, habitat restoration, and political action can be effective to save species in steep decline. 

The study serves, in many ways, as a wake-up call. By making the dramatic losses concrete, Rosenberg hopes people will be jolted into action. Today, Cornell and its partners (which includes the National Audubon Society) launched the website 3BillionBirds.org to share the findings and promote bird-saving solutions, including seven steps that anyone can take in their own lives. 

“The takeaways are that this is disturbing and that we need to do something soon,” Michel says. “But we’re seeing wonderful reasons for hope as well.”

Habitat Breakdown

Western Meadowlark. Photo: James Halsch/Audubon Photography Awards

1. Grasslands: These are among the most threatened biomes on the planet. Loss of habitat to urban and agricultural development, along with liberal pesticide use, has had detrimental effects on the birds that rely on these habitats. The study found that grasslands have lost nearly 720 million birds since 1970—a greater than 40 percent decline.

Spotlight Bird: The Western Meadowlark is widespread across grasslands in the western United States, Mexico and Canada. These yellow-bellied birds feed primarily on insects and seeds, often probing the soil with its bill to find food. This meadowlark is still common, but trends show populations have declined in recent decades.   

Evening Grosbeak. Photo: Kathy Webb/Great Backyard Bird Count

2. Boreal forest: Clearing for oil and gas development, logging, widespread fires, and climate change all threaten boreal forest habitat. It has also historically been difficult to monitor boreal forest species and the threats to them. Some 500 million birds have been lost in this habitat since 1970—a more than 30 percent decline.

Spotlight Bird: In the last century or so, the Evening Grosbeak spread from its historic territory in the western United States and Canada to conifer forests in the eastern side of the continent. These chunky-billed finches eat mostly seeds, including in backyard feeders. Although still common across their range, grosbeak numbers have taken a hit in recent decades and the eastern population has started to decline for unclear reasons.  

Dark-eyed Junco. Photo: Rebecca Fackrell/Great Backyard Bird Count

3. Forest Generalist: Habitat loss and fragmentation are a major issue in all forests. Logging, wildfires, and human development all threaten to carve up North America’s woods. Warming temperatures could also change the plant composition of forests. About 482 million individuals have been lost since 1970, a nearly 20 percent loss, according to the study.

Spotlight Bird: Dark-eyed Juncos can be found across nearly every forest of the United States, Canada, and Alaska. While considered one species, these sparrows come in several different color patterns depending on the region. The birds are still very widespread, but this study indicates there are still considerably fewer juncos today than there were 50 years ago.  

White-crowned Sparrow. Photo: Matthew Endersbe/Audubon Photography Awards

4. Habitat Generalist: These birds thrive in at least three different kinds of habitat. The considerable loss of generalists that thrive across biomes and across the continent point to multiple factors chipping away at bird populations gradually, over time.  About 417 million birds have been lost since 1970, the study estimates— a more than 20 percent loss.

Spotlight Bird: White-crowned Sparrows are common birds that nest across Alaska and Canada, and south along the Pacific Coast and mountains of the West. In winter, they spread across the southern states and into Mexico. Named for the black and white stripes on their heads, these birds fascinate scientists with the distinct local dialects in different regions. While still considered widespread, the analysis found this species has fewer individuals among its ranks.

Wood Thrush. Photo: Nate Rathbun/USFWS

5. Eastern Forest: This biome includes all forests south of the boreal forest in Canada and the eastern United States. Many of these forests were cleared in the 1800s and then regrown in the 1900s. Logging, clearing for development, and climate change all affect these forest landscapes. What’s more, many forest songbirds are migratory and winter in Central and South America, where they are facing threats that scientists are just beginning to understand. About 167 million birds have been lost since 1970, the study estimates— a more than 20 percent loss.

Spotlight Bird: The Wood Thrush breeds in forests in the eastern United States and Canada and migrates south to spend the winter in the tropical forests of Central America. Populations have been declining for decades, raising concerns among conservationists. The spotted-bellied birds are susceptible to nest parasitism from cowbirds and may also be suffering from habitat loss in their winter range.  

Pinyon Jay. Photo: Pam Koch/Great Backyard Bird Count

6. Western Forest: Western forests are all those south of the boreal in western Canada and the United states, and including the mountain forests of northern Mexico. Wildfire is a bigger threat in western forests than it is in eastern forests. These forests also face threats from logging, clearing for development, fragmentation, and climate change. About 140 million birds have been lost since 1970, the study estimates— a nearly 30 percent loss.

Spotlight Bird. True to its name, Pinyon Jay feed mainly on seeds on pinyon pine in the pinyon-juniper forests of the western United States. As such, the range of these dusty blue birds is closely tied with the fate of this unique habitat. Drought, insects, heat, and habitat loss all threaten the trees and the jays.  

Snowy Owl. Photo: Karyn Schiller/Audubon Photography Awards

7. Arctic Tundra: Climate change looms large over the tundra and is the primary threat to this nesting habitat for many birds. Warming temperatures melt permafrost and threaten to put migrating birds out of sync with the food they depend on during the brief northern summer. About 80 million birds have been lost since 1970, the study estimates—a more than 20 percent loss—though there is a wide range of uncertainty in this habitat due to data collection challenges.

Spotlight Bird: Snowy Owls breed on the open tundra of the Arctic and spend their winters in the balmy climes of Canada, Alaska, and the northernmost regions of the United states. Its nests are merely an unlined depression in the tundra. With this ecosystem warming faster than any other part of the globe, continued changes could further affect this species’ breeding success.   

Cactus Wren. Photo: Megumi Aita/Audubon Photography Awards

8. Arid Lands: Land clearing for urban expansion is a big threat to this habitat, as major southwestern cities like Phoenix grow. Oil and gas development also threaten to take out swaths of this habitat. About 35 million birds have been lost since 1970, the study estimates— about a 15 percent loss. 

Spotlight Bird: True to their name, Cactus Wrens often build nests in cacti in the arid southwestern United States and Mexico. These sociable birds like to hang out in pairs or family groups and making loud, raspy calls. Although still generally considered widespread, the birds may be declining in parts of their range in Texas and California. 

Sanderling. Photo: Traci Sepkovic/Audubon Photography Awards

9. Coasts: Human activity—like driving on the beach, letting dogs and kids run loose on the beach, bringing gull-attracting food to the beach—can disturb birds attempting to incubate eggs and raise chicks. Climate-related factors pose a threat as well, as sea-level rise encroaches on nesting grounds and an uptick in tropical storms washes out beaches. The study estimates about 6 million birds have been lost in this habitat since 1970. However, many coastal birds weren’t included in the analysis because there wasn’t enough robust population data, says Rosenberg. And some species the scientists looked at, like Oystercatchers, actually showed population increases over time.  

Spotlight Bird: While these small sandpipers breed only on high Arctic tundra, Sanderlings are commonly seen scurrying up and down beaches of the Atlantic, Pacific, and Gulf Coasts of North America for most of the year. Scientists think these birds are declining, owing at least in part to their reliance on a few specific stopover habitats during migration.

Wood Duck. Photo: Scott Suriano/Audubon Photography Awards

10. Wetlands: Some wetland species, waterfowl in particular, have seen population gains over the last few decades due in large part to political action and careful land management and restoration. Not all wetland birds have thrived, however. Marsh birds in particular have struggled as their habitat is drained for development, the ocean encroaches on coastal marshes, and contamination of chemicals and heavy metals as well as invasive species make these habitats less than suitable. The study estimates that this habitat has gained 20 million birds since 1970, an increase by more than 10 percent.

Spotlight Bird: Magestic Wood Ducks are found in wooded ponds, swamps, and rivers across the United States and some areas of Canada and, occasionally, Mexico. In the late 19th century, Wood Duck populations took a serious hit from habitat loss and hunting pressure. The ongoing recovery of Wood Duck populations is held up as a win for wildlife management.

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Bald Eagle. Photo: Don Berman/Audubon Photography Awards