A billion birds have disappeared from North America since 1970, and a third of bird species across the continent are threatened with extinction, a new report says.

The first State of North America's Birds report finds that of 1,154 bird species that live in and migrate among Canada, the U.S. and Mexico, 432 are of "high concern" due to low or declining populations, shrinking ranges and threats such as human-caused habitat loss, invasive predators and climate change.

Steven Price, president of Bird Studies Canada, a member of the North American Bird Initiative behind the report, says that since 1970, "the estimate is we've lost at least a billion birds from North America…. The trend lines are continuing down. They have to be turned around or will fall below a threshold where they can be recovered."

Ocean birds like northern gannets are among the most threatened, a new report suggests. Many that nest in Canada migrate to the Gulf of Mexico and were hard hit by the 2010 oil spill.

Most threatened, with more than half the species of "high concern" are ocean birds such as northern gannets, tropical and sub-tropical birds, including many that breed in Canada and the U.S., but winter in Mexico.

There are also steep declines in coastal shorebirds like semipalmated and western sandpipers and red knots, which have lost 90 per cent of their population; grassland birds such as the greater sage grouse, Sprague's pipit and chestnut-collared longspur; and aridland birds.

Once one of the most common forest birds in eastern North America, the wood thrush has decreased by almost 70% in the last 40 years. Wood thrushes and many warblers breed in Canada's forests, but winter in tropical forests of Mexico that are threatened by logging. ((Isaac Sanchez))

The North American Bird Conservation Initiative is a collaboration of conservation groups and scientists, in all three countries. The report was released partly to mark the 100th anniversary of the 1916 Migratory Bird Convention between Canada and the U.S. Information in the report is based on data collected by citizen scientists through bird surveys and counts since the 1970s and analyzed over the past 18 months.

It follows a similar report that focused on Canada in 2012 and found a 12 per cent drop in bird populations since 1970.

But because many birds make very long migrations, Canada's birds are "not really Canada's — they're shared across three nations," said Price.

For example, northern gannets nest in four colonies on Canada's East Coast, but migrate to the Gulf of Mexico, where they "got hit very hard by the Gulf oil spill" in 2010.

Waterfowl such as wood ducks are making a big comeback due to wetland habitat protection and hunting restrictions. (Sean Kilpatrick/The Canadian Press)

Wood thrushes and many warblers breed in Canada's forests, but winter in tropical forests of Mexico that are being logged.

Many grassland birds rely on habitat that run from Canada's Prairies down to Mexico's Chihuahuan grasslands — nearly 70 per cent of birds that migrate between the northern and southern grasslands have disappeared since 1970.

"It's our North American Serengeti," Price said of the region. "We have so many endangered birds or birds in decline because we have really dissected and divided the grasslands and prairies."

Some birds also face domestic threats — many coastal birds on the Haida Gwaii islands on Canada's West Coast are threatened by invasive predators such as raccoons and rats. They include species like the ancient murrelet, Cassin's and rhinoceros auklets, the fork-tailed storm petrel and the black oystercatcher.

The report did have some good news. Populations of waterfowl such as wood ducks and canvasbacks and birds of prey such as the osprey and peregrine falcon continue to rebound. Wetland habitat protection, hunting restrictions and bans of pesticides such as DDT have helped bring them back.

Populations of birds of prey such as osprey are also rebounding since the pesticide DDT was banned and hunting restrictions were put in place. (Rodney Saigeon)

"It's surprising that trend still continues to improve," Price said, adding that it offers hope for other species.

He said governments and industries in all three countries need to be thinking about habitat protection throughout the Western Hemisphere and other strategies to help bird populations stabilize and recover.

In addition to tackling problems such as invasive island predators at home, he added, Canada should be helping out nations in Latin America where many of our birds migrate.

"It's in our self-interest to help abroad because our birds are overwintering there."