Nearly 3 billion birds have disappeared from North America since 1970, new research shows, with even common species like sparrows and blackbirds suffering massive declines — a “sobering” new chapter in the global biodiversity crisis.

Most public attention is focused on extinctions, when all individuals of a species disappear forever. But the team behind the new research, published Thursday in the journal Science, instead undertook a detailed accounting of gains and losses for 529 species of birds in Canada and the United States using long-running surveys and a network of weather radars.

They found a decline of 29 per cent over five decades — a net loss of 2.9 billion individual birds out of approximately 10 billion alive in 1970. Biologists and ecologists have long known that many bird species are in decline, but the Science paper offers a startling new perspective on the magnitude of the problem.

“That 3 billion number was — wow,” said Adam Smith, a study co-author and senior biostatistician at the Canadian Wildife Service, Environment and Climate Change Canada.

Forest birds, grassland birds, shorebirds, and even invasive species — birds that inhabit incredibly diverse environments — all suffered massive declines, he points out. Sparrows, blackbirds, and finches accounted for a huge chunk of the total loss.

“Common birds, that we still see almost everywhere we go, even those species are in decline.”

The dwindling of even common species raises concerns about the scarcity of animals who play a critical role, and also fears that this pattern may not be exclusive to birds.

“They’re integral components of every ecosystem. They do pest control, pollination, seed dispersal,” says Ken Rosenberg, the study’s lead author and a conservation scientist with the Cornell Laboratory of Ornithology and the American Bird Conservancy.

“They’re so interwoven with everything else that if we’re seeing this loss and degradation in birds, we can be pretty sure that it’s happening with other groups, and that it’s a symptom of a much larger problem in the environment that will ultimately affect people.”

At the same time, the research offered a clear signal that conservation efforts have worked for some birds once considered on the precipice of extinction.

“We genuinely do have hope,” Rosenberg says.

The research team pulled from a dozen extensive North American bird surveys, most of which are carried out by volunteer bird enthusiasts.

The Audubon Christmas Bird Count, one of the longest-running citizen science efforts in the world, has been conducted every winter since 1900. The North American Breeding Bird Survey, the biggest data source for this paper, relies on skilled birders observing species along pre-set routes in Canada and the U.S.

“Because we can see them, they’re so conspicuous, so many people know birds and love birds, we can actually count them. We have better data on birds than we have on any other group of organisms in the world, so that allows us to see this picture,” says Rosenberg.

The researchers also drew on data from a network of 143 radar stations across the U.S., which accidentally capture enormous amounts of information on birds flying overhead as radars scan the sky for weather patterns. The radar data, a totally different monitoring technique, confirmed the same trends as the survey data, indicating a drop of 13.6 per cent of night-migrating birds since 2007.

The worst-hit group was grassland birds, which inhabit the same ecosystems that humans have increasingly converted for agriculture. Some 700 million grassland birds have disappeared since 1970.

Habitat loss is a huge problem for these species — grassland birds are being “squeezed out” of these landscapes as agriculture expands and intensifies, Rosenberg says — but new Canadian research also offers another worrying cause.

In a paper published in last week’s issue of Science, York University’s Bridget Stutchbury and her co-authors from the University of Saskatchewan showed that songbirds exposed to imidacloprid, a neonicotinoid insecticide, exhibited weight loss and delays in migration, one of the first direct links between a widely used pesticide and the long-observed decline in migratory birds.

“When I see this big picture, I think, what is happening? Why are birds declining, despite all our efforts?” asks Stutchbury.

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The new paper found birds with the longest-distance migrations tend to be faring worse. Stutchbury points out they touch down in so many different states along their journey that there is no simple answer on what is needed to stabilize these populations.

While the negative effects of neonicotinoids on bee populations is well-known, Stutchbury says scientists are just beginning to understand the link between these pesticides and declining bird health. But she also notes the causes of the losses are also diverse and global: wildfires in the Amazon, where many species of birds winter, also play a role, for example.

“The new study shows the huge scope of the bird decline problem in North America. It’s really sobering to see the numbers,” says Stutchbury.

The study also offered a beacon of hope. Wetland birds like ducks, geese and swans showed an overall gain since 1970 — evidence, the scientists say, that conservation efforts targeting these landscapes have worked.

“That’s a really encouraging story,” says Paul Smith, a research scientist with the National Wildlife Research Centre, Environment and Climate Change Canada, and another study co-author (no relation to Adam Smith.)

Wetland conservation is very advanced in North America, Paul Smith says, and is supported in part by funding from the sale of duck hunting licences.

“Over the last 50 years we’ve seen a significant increase in the amount of protected wetlands and there’s been efforts to restore those wetlands. The return of waterfowl in response to these conservation efforts is one of the conservation success stories.”

Hawks, falcons and other birds of prey, whose populations crashed in the 1970s, have rebounded since DDT was banned: they also showed a net gain.

Rosenberg emphasizes individuals can be part of the solution, by keeping their cats indoors, making windows bird-safe, replacing grass lawns with native plants, and buying bird-friendly shade-grown coffee, among other actions.

Ultimately, solutions will have to be both local and multi-state, experts say.

“It’s important to recognize the fact that Canada is the breeding grounds for a very large number of species that are shared at other times of the year with other countries throughout the western hemisphere,” says Paul Smith.

“Whether or not we’re responsible, the shared nature of migratory birds, and the worrying nature of these trends, means we need to work together to conserve them.”