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