Tufted Puffin. (Alan Burger/Special to QMI Agency)

Nearly half of Canada's bird species are significantly declining in numbers, and there are 12% fewer birds now than in the seventies, a new report has found.

While some of the country's 451 regularly occurring native species are doing well, more species are showing decreases (33% versus 44%), and human activity is responsible in all cases, concluded the State of Canada's Birds report released Wednesday.

Raptor species, like falcons and bald eagles, have bounced back since 1970, largely due to pesticide controls and other conservation measures. Waterfowl populations have also done well thanks to wetland management.

But grassland birds (like meadowlarks and grouse) and aerial insectivores (like swallows and flycatchers) have declined steeply. Some formerly very common species like the barn swallow and the chimney swift are down to less than a quarter of their 1970-level populations, the report said. And "urgent action" is needed to protect shorebirds, which have declined by almost half.

There are 66 bird species currently considered endangered, threatened or of "special concern."

Loss of habitat is primarily to blame, mainly due to clearing forests, converting grassland to farms, over-harvesting and general urban and industrial development. Climate change is also a factor.

"In recent decades, increasing human populations in Canada and elsewhere are putting pressures on bird populations that may exceed their ability to cope," the report said.

The health of bird populations is important because it's an indicator of the overall health of the environment.

The report was compiled by the North American Bird Conservation Initiative in Canada (NABCI-Canada), which is made up of experts from government, conservation groups and private sector organizations.