The Conservation Column
By Pepper Trail
October’s column is from the National Audubon Society, and covers a major new analysis of North American bird populations. The study, just released, confirms what long-time birders know: bird populations are in steep decline in virtually every habitat and every part of the country. Time to redouble our efforts!
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.
By Jillian Mock, from www.audubon.org
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. 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.
Despite gaps in the data, the overall picture is clear, especially because the radar and survey results tell the same story of losses, says Nicole Michel, a senior quantitative ecologist with the National Audubon Society. “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.
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. 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.
“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.
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, like the Western Meadowlark. The study found that grasslands have lost nearly 720 million birds since 1970—a greater than 40 percent decline.
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, like the Evening Grosbeak. Some 500 million birds have been lost in this habitat since 1970—a more than 30 percent decline.
3. Forest Generalist: Habitat loss and fragmentation are a major issue in all forests, home to birds like the Dark-eyed Junco. 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.
4. Habitat Generalist: These birds, for example, the White-crowned Sparrow, 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.
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, like the Wood Thrush, 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.
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, home to species like the Pinyon Jay. 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.
7. Arctic Tundra: Climate change looms large over the tundra and is the primary threat to this nesting habitat for many birds, like the iconic Snowy Owl. 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.
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, vital for birds like the Cactus Wren. About 35 million birds have been lost since 1970, the study estimates— about a 15 percent loss.
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.
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.
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.”