Zoology 10th Edition by Stephen Miller,John Harley

Exercise 2

The bodies of birds are covered by two kinds of feathers. Pennaceous feathers create aerodynamic surfaces. Plumulaceous feathers include insulating down feathers. There are numerous modifications of the bird skeleton for flight. Some bones have large air spaces and internal strutting. More cervical vertebrae create a very flexible neck. Other modifications help keep the skeleton in a flight posture and serve as points of attachment for muscles and feathers. Wings of birds form an airfoil, and wing movements provide lift and forward movement. Birds sustain endothermy and rapid metabolism by high rates of food consumption and digestion. Bird lungs contain parabronchi, which promote efficient gas exchange in a one-way movement of air across exchange surfaces. The forebrain of birds is large, and birds rely on visual and auditory senses. Birds are oviparous and females possess a single ovary. Most birds are monogamous; others are polygynous or polyandrous. Altricial hatchlings are helpless and dependent on their parents during early growth. Precocial hatchlings are alert, lively, and able to feed themselves. Birds migrate to avoid climatic extremes and secure adequate food, shelter, and space throughout the year. Birds navigate using route-based navigation and location-based navigation.
Why is flight much more complicated than just flapping wings?