鸟类是温血动物，这意味着它们可以独立于环境,保持它们的体温。然而，当环境实在是冷的时候,它们会挤在一起取暖。
They huddle together in such roosts for warmth, the most dominant birds taking the center positions, forcing the immature and more subordinate to the edges where they are at the mercy of the elements.
