This bird may migrate for more than a thousand miles, sometimes in only a few days. A birds metabolic rate during flight is about 10 times as high as the resting metabolic rate. There is an optimum speed of flight at which oxygen consumption is at a minimum which varies depending on species. Flying slower or faster than this speed uses more oxygen, therefore is less efficient. The skeletal structure of a bird is uniquely built for flight.
Bird bones are very light and filled with air.