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.

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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.