Nature World: Massive bird invasions taking place across the United States and Canada, a phenomenon that has long puzzled scientists and birdwatchers alike, is reportedly linked to climate shifts, new research indicates.
Over the years, vast numbers of birds from Canada's boreal forests have migrated hundreds-of-thousands of miles south from their usual winter range. While previous studies have blamed these so-called irruptions on food shortages, it seems that climate also plays a role. Specifically, persistent...