Relying on their own bodies for warmth, birds and men need not turn to the natural environment to soak up warmth, and so in frigid lands they fare better than cold-blooded creatures.
鳥與人，都靠自己身上體溫取暖，不似依賴由自然環境吸取熱量的冷血動物，因此在寒冷地帶也有較強的生命力。