Washington Post: About half of America’s migratory birds fly from destinations as far-flung as Chile to nest in Canada’s boreal forest. In Alberta, that forest lies above tar sands that contain oil reserves second only to Saudi Arabia’s. The excavation of the tar sands — projected to pump $2.4 trillion into Canada’s economy between 2010 and 2030 — could reduce the region’s migratory-bird population by almost half, according to a peer-reviewed study released Dec. 2 by U.S. and Canadian environmental …