Wood Thrush checks the brush. (Frank Leung/Getty Images)

More than a third of all North American bird species are at risk of becoming extinct unless significant action is taken, scientists who are part of a tri-nation initiative reported Wednesday, adding that ocean and tropical birds were in particular danger.

The report by the North American Bird Conservation Initiative — the first of its kind to look at the vulnerability of bird populations in Canada, the United States and Mexico — said 37 percent of all 1,154 species on the continent needed urgent conservation action.

The governments of the three nations created the initiative in 1999.

More than half of the species tied to oceans and tropical forests are on a special watch list because of small and declining populations, limited ranges and severe threats to their habitats.

“The outlook for oceanic birds . . . is the bleakest of any North American bird group,” said the report, which blamed invasive predators — such as rats and cats — on nesting islands as well as overfishing, pollution and climate change.

Ways to address the problem include removing predators, expanding protected marine areas and reducing the oceans’ deposits of plastic products that can trap or choke birds, the report said.

Many species in coastal, grassland and arid habitats are declining steeply, in particular long-distance migratory shore birds. The main causes are sea-level rise, coastal development, human activity and oil spills, the report said.