Bird species are in "big trouble" worldwide, a sign that the planet's health is also faltering, according to a new report released today at the International Union for Conservation of Nature (IUCN) meeting in Barcelona, Spain.

Not only are rare birds getting rarer, but migratory songbirds, seabirds, and even common backyard birds are also plummeting, according to the State of the World's Birds, a report by the U.K. nonprofit BirdLife International.

The loss could have far-reaching consequences, according to scientists and policy makers.

Like the proverbial canary in a coal mine, the nearly 10,000 known bird species act as "environmental barometers" whose populations can appraise the greater well-being of their habitats.

"There's a serious erosion of biodiversity around us," Leon Bennun, director of science and policy for BirdLife International, said during a briefing at the IUCN's congress.

"It's a signal we should be picking up and not ignoring."

However, Bennun and others pointed out that conservation action can keep birds from disappearing—16 bird species have been saved in the past ten years, for instance.

BirdLife's Muhtari Aminu-Kano added, "It's not all stories of doom and gloom, but there's little reason to cheer about what's happening to biodiversity."

Scary Finding

One in eight of the nearly 10,000 known bird species are threatened, according to BirdLife data included in the 2008 IUCN Red List. More than 150 of bird species have vanished since 1500, the report noted.

(See photos of species on the 2008 Red List.)

But the rapid deterioration of common birds is "one of the scariest things" to come from the findings, said Tim Blackburn, director of the Institute of Zoology at the Zoological Society of London.

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SOURCES AND RELATED WEB SITES Zoological Society of London's Institute of Zoology BirdLife International IUCN