SOURCE: New York Times

DATE: September 19, 2019

SNIP: The skies are emptying out.

The number of birds in the United States and Canada has fallen by 29 percent since 1970, scientists reported on Thursday. There are 2.9 billion fewer birds taking wing now than there were 50 years ago.

The analysis, published in the journal Science, is the most exhaustive and ambitious attempt yet to learn what is happening to avian populations. The results have shocked researchers and conservation organizations.

In a statement on Thursday, David Yarnold, president and chief executive of the National Audubon Society, called the findings “a full-blown crisis.”

Experts have long known that some bird species have become vulnerable to extinction. But the new study, based on a broad survey of more than 500 species, reveals steep losses even among such traditionally abundant birds as robins and sparrows.

Common bird species are vital to ecosystems, controlling pests, pollinating flowers, spreading seeds and regenerating forests. When these birds disappear, their former habitats often are not the same.

There are likely many causes, the most important of which include habitat loss and wider use of pesticides.

Kevin Gaston, a conservation biologist at the University of Exeter, said that new findings signal something larger at work: “This is the loss of nature.”

While some species grew, the researchers found, the majority declined — often by huge numbers.

“We were stunned by the result — it’s just staggering,” said Kenneth V. Rosenberg, a conservation scientist at Cornell University and the American Bird Conservancy, and the lead author of the new study.

“It’s not just these highly threatened birds that we’re afraid are going to go on the endangered species list,” he said. “It’s across the board.”

The new study was not designed to determine why birds are disappearing, but the results — as well as earlier research — point to some likely culprits, Dr. Rosenberg said.

Grassland species have suffered the biggest declines by far, having lost 717 million birds. These birds have probably been decimated by modern agriculture and development.

“Every field that’s plowed under, and every wetland area that’s drained, you lose the birds in that area,” Dr. Rosenberg said.

In addition to habitat loss, pesticides may have taken a toll. A study published last week, for example, found that pesticides called neonicotinoids make it harder for birds to put on weight needed for migration, delaying their travel.

The sheer scale of the bird decline meant that stopping it would require immense effort, said Dr. Young, of the University of California, Santa Barbara. Habitats must be defended, chemicals restricted, buildings redesigned. “We’re overusing the world, so it’s affecting everything,” she said.