Hardship is nothing new for birds. Birds are adapters. They flock or they fly alone. Some migrate thousands of miles, knowing when to go and how to get there. Others tough it out, camouflaging themselves to match their winter surroundings and eating what they can rustle up.

These facts, well known to most human children and adults, make it all the more shocking to hear that there are 2.9 billion fewer birds in the skies over North America than in 1970. Even the scientists who collected the data were caught off guard by the magnitude of the decline. They analyzed a half-century of evidence, including citizen birdwatchers' reports and 11 years of data from 143 NEXRAD radar stations that spot large masses of migratory birds flying at night.

Their findings, published in the journal Science, note that the losses are across the majority of North American bird species, not just among those already known to be endangered or threatened. Similar results are coming from Europe. Ninety percent of the declines are among familiar backyard birds — sparrows, warblers, finches and swallows. It all translates to a net loss of 29% of the breeding birds, meaning that many more have died than have hatched and survived. 

The authors identified likely causes by the declines in numbers in certain habitats. They say North American forests have lost 1 billion birds; grasslands, 720 million; insect-eaters are down 160 million; coastal shorebirds, down by one-third; and in the last decade, spring migration numbers off by 14%. The scientists, who include researchers from Audubon, the Smithsonian and the Cornell Lab of Ornithology, put partial blame on disappearing habitats, such as when forests are cleared or land is converted for agriculture, development or mining, and no longer supports the food or water birds depend upon.

Within human habitats birds are dying because of those superb hunters, domestic cats, and from collisions with windows, vehicles, communication towers or wind turbines. Pesticides and warming climates cut down on insects and plants — the birds' grocery store. 

Unlike many reports of gloom, this one moves beyond doom to a call to action. It offers ways that ordinary householders can lessen the risks to birds, such as keeping cats indoors and making windows less invisible to birds by day and night. They have organized a movement, #BringBirdsBack, citing the huge successes humans have made in bringing back ospreys, eagles and other raptors after Rachel Carson warned of the lethal effects of the pesticide DDT in her book, "Silent Spring." The 1973 passage of the Endangered Species Act, which the Trump administration has said it will curtail, made it possible.

Conversely, North Americans failed to grasp that passenger pigeons, once by far the most numerous bird population on the continent, had fallen to dangerous levels at the turn of the 20th century. They had been hunted down to three flocks, and finally one last female named Martha, who died at the Cincinnati Zoo 105 years ago.

The expression "canary in the coal mine" describes an avian warning system for miners who would not notice a build-up of carbon monoxide or other lethal gas until they were too weakened to escape. If the canary died, it was a sign to act fast. It still is.

What's bad for birds is bad for humans. The Audubon Society has observed that when birds don't thrive in urban neighborhoods, those are the same places that are unhealthy and unsafe for people. Birds have been inhabiting earth's waters and skies since they shared the world with the dinosaurs. They survived when the dinosaurs did not, and they can rebound now.

No humans existed when the dinosaurs died out. We could not have saved them  — or ourselves. When the last passenger pigeon died, it was because humans failed to realize the consequences of their actions or to stop the killing. The best they could do was to shelter Martha in a zoo. 

Communities, developers and all levels of government should insist on standards for lessening the environmental impact of new construction, and use the best science available to site towers and turbines. Keep the rules for the Endangered Species Act intact. We must help undo some of our own unintended consequences for the birds. We need them. #BringBirdsBack.

The Day editorial board meets with political, business and community leaders to formulate editorial viewpoints. It is composed of President and Publisher Timothy Dwyer, Executive Editor Izaskun E. Larraneta, Owen Poole, copy editor, and Lisa McGinley, retired deputy managing editor. The board operates independently from The Day newsroom.