Bird flight fascinates me. The wing is both an instrument of power and a specialized surface that generates the lift that carries them aloft.
The feathered surface of the elongated forearms is central to flight, and humans have tried to copy the principles of avian flight in designing aircraft. Two forces govern the operation of the wing in generating flight: lift provided by the differential air masses moving over the upper and lower surface of the wing and frictional drag induced by the bird’s body (and wing) moving through the air. To optimize flight, birds need to maximize lift, while minimizing drag.
Some examples of how this is accomplished. Birds can reduce drag by presenting as little body surface to the airstream as possible, as illustrated by the flattened profile of an Anhinga, with its outstretched neck in perfect alignment with its body and tail. Airflow is directed rapidly over the relatively flat upper surface of the bird, reducing air pressure there, and causing the body to rise.
Ducks, Geese, Swans, and Cranes adopt the same strategy (flying with outstretched neck) to minimize frontal drag, but long-necked wading birds (Herons and Egrets) double-up their necks while flying. This doesn’t seem as aerodynamically efficient, but these species don’t tend to fly long distances, anyway.
Lift is directly related to wing surface area — the more area, the greater the lifting power. Long, wide wings make the best lifters, as seen in hawks, eagles, vultures, pelicans, albatross, etc.
But big, long wings dictate slow, coursing flight, and some birds need to get there faster or make quick changes in direction as they chase prey or evade predators. Most song birds, pigeons and doves, parrots, and a few raptorial birds like Accipter hawks and Falcons have short, round (elliptical) wings that enable high maneuverability and agility while flying. Lift is generated by the wing as it forces the air mass under it down. Pectoral muscle contractions generate the power both to move forward and to move up in the air column.
The king of speed (Peregrine Falcon) has the short, swept-back wings of a fighter plane. Its flat flight profile reduces drag, but the key to its success is its short but powerful wings that allow the bird to change direction rapidly as it chases its prey.
And how about the ability remain stationary in mid-air or to even fly backward?
Hummingbird wings move in a figure-eight pattern back and forth above the plane of its body, and the mobile shoulder allows the wing to rotate so that it presses down on the air mass both on the down-stroke and on the up-stroke of the wing beat. So, unlike other birds that develop almost 100% of their lift during a downward wing flap, hummingbirds can generate up to 25% of their lift during the up-stroke was well.
For some really spectacular photos for birds in flight, please check out Phil Lanoue’s Photography (e.g., October flights). At the end of each month, Phil showcases some of the dramatic photos of airborne birds he has shot that month.