CALGARY, Alberta: A coalition of North American environmental groups says the development of Canada's oil sands region threatens to kill as many as 166 million birds over the next five decades and is calling for a moratorium on new projects in the region.

The coalition's groups, which include the Natural Resources Defense Council, the Boreal Songbirds Initiative and the Pembina Institute, say petroleum-extraction projects in the oil-rich region of northern Alberta are a threat to migratory birds and the boreal forest they rely on.

Their study concluded that development of the oil sands, would be fatal for 6 million to 166 million birds because of habitat loss, shrinking wetlands, accumulation of toxins and other causes.

The solution, the groups say, is to halt new projects in the oil sands and to clean up existing facilities. They are also calling for strengthened regulations to protect Canada's vast boreal, or northern, forest and for Alberta, whose government has backed oil sands developments, to prove the resource can be exploited without serious environmental harm.

"People need to take a hard look at whether this can be mitigated or if tar sands development is just incompatible with conservation of bird habitat," said Susan Casey-Lefkowitz, a senior attorney with the Natural Resources Defense Council.

The report estimates about half of North America's migratory birds nest in the boreal forest and between 22 million and 170 million birds breed in areas that could be subject to oil sands development.

The oil sands contain the biggest oil reserves outside the Middle East but the crude is expensive and difficult to extract. Mining projects strip large areas of land to access the oil-laden soils below the surface.

While the report has not yet been made public, the Canadian Association of Petroleum Producers, which represents the country's big oil firms, said the oil sands industry complies with environmental regulations and dismissed calls for a moratorium.

"We need a balanced conversation, supported like a stool with three legs, environment, economy and energy," David Collyer, the association's president, said in a statement. "Calls for a moratorium that consider only one leg of the stool, in a vacuum, are not constructive."

Developments in the region have been criticized for pumping large amounts of greenhouse gases into the atmosphere, using too much water and being harmful to wildlife.

Indeed, the death of about 500 ducks earlier this year after they landed on a toxic tailings pond operated by Syncrude Canada Ltd, the biggest oil sands producer, brought international attention to the region.

The environmental groups' forecast is based on a big expansion of oil production from the region. The oil sands currently produce more than 1 million barrels a day, but the report is based on an eventual output of 5 million barrels a day, in line with industry forecasts of production in two decades or more.