Canada's bird populations have a new predator: climate change.

According to "The State of Canada's Birds," the first comprehensive report on the state of Canadian avian species, Canadian bird populations have declined by an average of 12 percent since 1970. While some species are thriving, 44 percent of Canada's more than 460 bird species are losing numbers.

Grassland birds, migratory shorebirds and birds that eat insects in flight are in the steepest decline. Each of these groups has decreased by more than 40 percent and some individual species have decreased by more than 90 percent, such as the prairie-dwelling McCown's longspur, which is now considered to be "at risk."

Climate models predict that the Canadian prairies will experience increased drought, which could strip away habitat for waterfowl. Farther north, flooding and fires are expected to jeopardize bird populations in the Canadian boreal forest.

The early arrival of spring in recent years has also caused experts to worry that migratory birds will return to Canada after their food supply has peaked.

The problem of synchrony

"One of the concerns is ... that climate change is happening so fast it's throwing out of synchrony the food supply and the cycle of migration," said Ted Cheskey, manager of bird conservation programs at the nonprofit Nature Canada and an author of the report, led by the multistakeholder group the North American Bird Conservation Initiative.

Although they are still relatively common species, aerial insect feeders, like barn swallows and chimney swifts, have declined by 64 percent compared with previous levels. Some experts attribute the fall to a climate shift that has caused insect populations to peak earlier in the year, limiting what adults can feed their young.

Arctic bird species are also having a tough time. The Arctic is changing faster than anywhere in the world, and that could have significant impacts on nesting practices and the overall survival of Arctic birds, given changes in food availability, increases in the number of predators and more frequent severe weather events.

Climate change is already affecting Arctic ecosystems at a rate the authors say could outpace the ability of some bird species to adapt.

However, some bird populations are soaring. The snow goose population, for instance, has increased by more than 300 percent, although the birds are now degrading Canada's salt marshes. Overall, 33 percent of Canadian bird species have experienced growth since 1970.

Arctic shorebirds plummet

Of those under threat, shorebirds that nest in the Arctic have fared the worst. Overall, shorebird populations have dropped by 60 percent, and 10 species are in severe decline. Experts say the fall is largely due to the degradation of resting sites along winter migratory routes, spurred in part by climate change.

Only about 20 percent of Canada's bird population stays in the country year-round, which makes the preservation of avian habitat a continental issue, said Cheskey. Building bird populations back up to previous levels will require collaboration across national borders, he said.

The authors conclude that protecting areas vital to bird survival that are also most resistant to climate change will help reduce the harmful impacts of human activity on bird populations.

"We know birds are good indicators of overall ecosystem health, so we want to use protecting those bird populations as a means of protecting ecosystems for us, as well," said Cheskey. "We are all part of the same ecosystem."

A similar report on climate change and the state of bird species in the United States was published in 2010.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500.