The role of climate change and food supply on winter populations of seed-eating birds

We studied the populations of four seed-eating bird species throughout winter during a 30-year study in forests Tatarstan Republic, Russia. Numbers all fluctuated from year-to-year by several orders magnitude but with significant underlying trend for increased numbers associated rising temperatures and greater food supply. question whether traditional view that such birds move further south only after exhausting supply is too simplistic. believe severity winter, or lack it, highly influential on mortality movements these characteristic boreal forest zone.