Bird populations plummet in the US and Canada

Bird populations have dropped 29% since the 1970s in the US and Canada, scientists reported on Thursday.

Researchers blamed habitat loss and degradation, the chemical eradication of insects, and cats.

"Birds are in crisis," said Peter Marra, director of the Georgetown Environment Initiative at Georgetown University and co-author of the study.

"The take-home message is that our findings add to mounting evidence with other recent studies showing massive declines in insects, amphibians and other taxa, signaling a widespread ecological crisis," Marra added. "Birds are the quintessential indicators of environmental health, the canaries in the coal mine, and they're telling us it's urgent to take action to ensure our planet can continue to sustain wildlife and people."

The paper, published in the journal Science, detailed how researchers tracked populations of 529 species using historical bird counts, and also weather radar data that showed declines in the volume of migrating birds.

Read more: The science of migratory birds

'Landmark paper'

Ornithological experts were quick to react to the alarming study results. "This is a landmark paper. It's put numbers to everyone's fears about what's going on," said Joel Cracraft, curator-in-charge of the Department of Ornithology at the American Museum of Natural History, who wasn't part of the study. "It's even more stark than what many of us might have guessed," Cracraft said.

More than 90% of the drop came from 12 mostly common species including sparrows, warblers, blackbirds, and finches.

The worst hit category of birds were grassland birds, dropping 53% due to agricultural intensification. Shorebirds, often migratory, dropped 37%, due to habitat degradation and the destruction of migratory destinations.

Migratory birds in general suffered a steep decline, particularly in bird species that migrate to the tropics.

The study matches similar results from other parts of the world, including Europe.

aw/kl (AP, Reuters, AFP)

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