Most avian characteristics are directly related to flight. The body is stream-lined to minimise air resistance. The fore-limbs (and usually the tail also) carry large special flight feathers to produce light mobile aerofoils. The skeleton has a remarkable combination of rigidity with lightness and the heavy organs like flight muscles, heart, liver and gizzard lie ventrally to bring the centre of gravity below the centre of the lift forces generated by the wings. This is necessary for stability in flight. But most important of all are the physiological adaptations to produce the rapid energy release necessary for powered flight. Birds have the heaviest heart relative to body weight, the highest blood temperature and the most efficient lung system of any land vertebrate. They also have a specialised digestive system utilising mainly high-energy foods.
Unable to display preview. Download preview PDF.