More Than Lost Feathers

If you were alive in 1970, more than one in four birds in the U.S. and Canada has disappeared within your lifetime. According to research published in *Science*, wild bird populations in the continental U.S. and Canada have declined by almost 30% since 1970.

Bird numbers naturally fluctuate, which explains changes from month to month, but many bird populations have been declining gradually and consistently for years. In a comprehensive 2019 study led by the Cornell Lab of Ornithology, researchers examined 529 bird species in the U.S. and Canada, finding a net loss of 2.9 billion breeding birds—or 29% of the overall population—since 1970.

These losses don’t just affect rare or endangered species; common birds have suffered the greatest declines, including beloved species like Dark-eyed Juncos (down by 168 million) and Red-winged Blackbirds (down by 92 million). “We were astounded by this net loss across all birds on our continent—the loss of billions of birds,” said Ken Rosenberg, a conservation scientist at the Cornell Lab who led an international team in analyzing population trends for 529 species. “Our results signal an urgent need...to avert continued biodiversity loss and potential collapse of the continental avifauna.”

This study, the first to compute total declines in bird populations across the U.S. and Canada, reveals a loss of 2.9 billion breeding adult birds. “These bird losses are a strong signal that human-altered landscapes are losing their ability to support birdlife,” Rosenberg said. “And that is a sign of a coming collapse of the overall environment.”

Birds play essential roles in ecosystems by pollinating wildflowers, dispersing seeds, and eating pest insects like bark beetles and weevils. In spring, migrating birds are even visible on radar, traveling high at night. Cornell Lab’s aeroecology specialist Adriaan Dokter analyzed radar imagery from spring migration, finding a 14% decrease in “bird biomass” since 2007, with the steepest declines in the eastern U.S.

The scale of loss portrayed in this *Science* study is unlike anything in modern natural history. While the Passenger Pigeon experienced catastrophic declines, this was one species; the current losses span hundreds of species from coast to coast. The population models in this study are based on decades of standardized bird-survey data, representing the most comprehensive synthesis of long-term monitoring data for any animal group, according to Adam Smith, a biostatistician at Environment and Climate Change Canada. “In less than a human lifetime, we’ve lost almost a third of our birds,” Smith said.

Forest bird populations alone have lost 1 billion birds, and grassland birds have collectively declined by more than 50%, losing over 700 million birds. Habitat loss, driven by agricultural intensification and development, is a major factor in these declines.

“This analysis shows we’re eating away at the foundations of our ecosystems,” said Arvind Panjabi, avian conservation scientist at the Bird Conservancy of the Rockies. “These numbers show that the world has changed significantly since 1970.” For Smith, the data calls for a major shift in conservation strategy. “This is a wake-up call for the need to move beyond single-species conservation. We’ve rescued species like the Trumpeter Swan and Peregrine Falcon, but now, given the extreme declines, we need a new approach. These ecosystems and biomes are in serious trouble.”

More than 90% of the total bird loss in the U.S. and Canada (over 2.5 billion birds) comes from just 12 avian families, including sparrows and blackbirds. Familiar backyard birds are among the hardest hit. For example, the Red-winged Blackbird has lost one-third of its population since 1970. “These so-called common birds—the species many people see daily—represent the greatest losses,” notes Peter Marra, director of the Georgetown Environment Initiative. “That’s reminiscent of what happened with the Passenger Pigeon, which no one thought could go extinct.”

Birds are indicators of broader ecological issues, such as habitat loss, pollution, and climate change. Monitoring bird populations helps us gauge the health of our environment. Rosenberg emphasizes the alarming decline in common birds: “We’re squeezing the planet so hard in terms of resource use and space. The last common birds on our landscapes are declining, and we’re losing hundreds of millions.”

Because declines are gradual, people may not notice the loss of abundance. “There’s a shifting baseline,” said Smith. “Since the declines are gradual, we lose track of just how abundant these birds used to be.” The study’s findings are clear: even some of America’s most familiar backyard birds are rapidly disappearing.

Nature is dynamic, and without human impact, some bird species would thrive while others would fade. But many of the biggest challenges birds face—habitat loss, pesticides, glass windows, and domestic cats—are man-made.

Not all news is dire; some bird groups are flourishing thanks to focused conservation. Raptors, waterfowl, and turkeys have benefited from conservation efforts. Birds of prey, like hawks and falcons, recovered thanks to policies like the banning of DDT and endangered species protections. Conservation funding has also bolstered game birds like the Wild Turkey.

Rosenberg points out that even with 30% of North America’s birds lost, 70% remain to drive a recovery if conservation efforts ramp up soon. “None of these declines are irreversible yet,” he says, “but that may not be true 10 years from now.”

The Western Meadowlark, in particular, has lost an estimated 40% of its population since 1970. Their iconic song signals the arrival of spring, bringing hope after winter. Without their melodic calls, we may lose one of nature’s most beloved signs of spring’s return.