Flight

Joe Meche is a member of the board of directors of the North Cascades Audubon Society and is in his eighth year as editor of the chapter newsletter. Joe is also a member of the board of directors of the Washington Brant Foundation. He has been photographing birds and landscapes for over 30 years and has been watching birds for more than 50 years.

When I was growing up and first beginning to notice things other than food and shelter, I’d spend hours watching hawks and vultures soaring effortlessly above the rice fields outside my hometown. Whether I was alone or with an equally-adventurous pal or a visiting cousin or three, I would take a break from aimless meanderings to lie flat on my back to watch the soaring birds. As male kids are quick to do, we’d occasionally pretend to shoot them out of the sky with the guns that we were years away from acquiring. But more often than not we watched with a sense of awe and a bit of envy. Our thoughts were usually along the lines of wondering how they could do that and wishing that we could!

Of all the fascinating characteristics of birds, perhaps the one that is most envied by humans is their ability to fly. Through millennia of evolution, the sine qua non is that birds, along with bats and flying insects, are the only members of the animal kingdom that are built for sustained flight. Bats perform at night and mostly out of sight; flying insects are somewhat difficult to observe and embrace; but birds are all around us and highly accessible. Interestingly enough, bats and birds both eat flying insects. Still, the birds capture our imaginations and the beauty of birds in flight is unequalled in the natural world.

Birds are not only capable of flying, but they are masters of the medium that surrounds us all. As fish are to water, birds are to the air. Birds are able to hover; they can achieve incredible speeds when diving; some can fly backward and even upside down; and some birds can soar for extended periods of time. Individual birds have evolved specific ways and means of flight that complement their habitat and diet. While a few species have evolved into flightless states to suit their needs, most birds fly—and often amaze those of us who are earthbound.

The primary principles of aerodynamics involve weight, lift, drag and thrust. To attain controlled, balanced flight, lift compensates appropriately for weight and thrust, in turn, counters the force known as drag. These principles apply to birds as well as to manmade aircraft. The essential elements required to fly take into consideration the perfect balance of the load and a suitable engine to power the load.

With these very basic concepts in mind, consider the avian structure as a whole to better understand how birds are able to fly and do it so effortlessly—or so it seems to us. Consider also how the early pioneers of aviation studied every aspect of birds in flight to solve the conundrum. Throughout the range of species, the flight of individual birds, while seemingly similar, varies accordingly. From the smallest hummingbird to the largest raptors and seabirds, adaptive evolution again plays an important part in the life of birds.

The avian body is a marvel of adaptive natural engineering, through evolution. Everything that needs to be attended to for sustained flight has been incorporated into birds’ bodies. The body houses the engine and provides strategic supports for the power to attain flight. Unlike the bones of earthbound mammals, for instance, birds’ bones are lightweight and air-filled. The skeleton itself is designed to withstand the stress incurred by the act of flying; and birds’ wings have hollow bones, which are unusually strong.

The breastbones of birds have a large keel that anchors the primary flight muscles and the bones are arranged in a triangular system of struts and supports that resists the pressure exerted by the wing strokes during flight. The power behind flight originates in two specific muscles—the supracoracoideus and pectoralis muscles. The former lifts the wing and the larger pectoralis muscle provides the power in the down stroke. The pectoralis muscle accounts for fifteen percent of the body mass of flying birds.

Within the avian engine, the rate of metabolic activity is extraordinary. Certain modes of flight, such as soaring, understandably place fewer demands on the system than the sudden, explosive bursts of some waterfowl and especially the heavier birds that require a longer runway for take-off. Birds are well practiced in the art of riding thermals to conserve energy. Formation flying also serves to conserve energy and the ‘V’ formations of migrating geese are a practical necessity for birds whose wings are smaller, relative to their body size.

In flight, the wing is the thing! The pitch of the wing, along with wing size and shape are integral parts of flying. Any one of us, who has defied our parents’ admonitions and held our hand out the car window, understands how the pitch or angle of our hand controlled the upward or downward movement. The same principle applies to the pitch of the wing, depending on the need at the moment, whether it’s the act of soaring or fleeing, taking off or landing. The pitch controls the forces of lift and drag by directing the airflow over the wings.

The size and shape of wings have evolved over thousands of years to accommodate the specific needs of each species. Birds that live in open country tend to have longer, pointed wings, while birds that frequent forested landscapes have wings that are shorter and more rounded. Consider the wings of a falcon versus the wings of a sharp-shinned hawk, for example. Both of these birds prey on smaller birds and their species-specific wings provide appropriate speed and maneuverability in their preferred habitats while pursuing prey.

Wing loading is the relationship between wing size and body mass. Most of our diving birds have heavier bodies that enable them to dive, but their proportionately smaller wings require that they run on top of the water while flapping their wings, to become airborne. This long-runway approach is also a necessity for larger birds such as swans and albatrosses. Either way and just as in manmade aircraft, the most energy expended is during takeoff. The other end of a flight also consumes a lot of energy, since the bird then has to slow down from its flight speed and go into what pilots refer to as a stall to ease into a safe landing.

The rate of wing beats required for birds to maintain balance and sustained flight is, again, specific to the individual species and the need at hand. The rate of wing beats for one species of hummingbird, for instance, is an astounding fifty-three strokes per second! Hummingbirds are also capable of hovering and backward flight. The metabolic rate of hummingbirds is simply incredible. It just goes to show what a diet with high sugar content will do for you!

With about 50 different muscles controlling movements of the wings, no aircraft ever made can approach the maneuverability of the average bird. While the wings are providing the majority of the power, the tails of birds also contribute to their overall success aloft. The tail adds to the lift and can be used as a rudder. Birds are also able to move their wings independently of each other, thereby facilitating turning and twisting while in flight.

Birds’ wings are the obvious equivalent of our arms, albeit with feathers. The same major bones that we find in our arms—the humerus, radius and ulna—can also be found in birds’ wings. The wings also include carpal bones and phalanges, or digits, to replicate our wrists and fingers. Since birds have to deal with the tradeoff of having no hands, their necks have additional vertebrae, which enable them to handle the simple chores of retrieving objects such as nesting materials, as well as feeding and cleaning with their beaks and bills.

The principal composition of the feather structure on the wings is similar in all species and includes two specific groups of feathers. The primaries are the longer feathers and are found near the wingtips, on the wrists and fingers. The secondaries are the feathers that are closer to the body of the bird, on the forearm. The tail feathers are also longer and, along with the primaries, are considered the actual flight feathers. Feathers are the final touch to one of nature’s most fascinating evolutionary adaptations—the ability to fly!

If you’re interested in a good place to observe birds in all aspects of flight, spend some time at any of the local waterfront areas frequented by gulls. While gulls are not exactly everyone’s idea of glamour birds, their accessibility and command of the principles of flight will provide a good primer. Summertime is also a good time to expand your studies of avian flight to the spectacular Caspian terns, the largest member of the tern family. Terns provide an extra bit of excitement when they depart from their flight plans to dive for fish.

Is there a better way to spend time in any number of locations than to simply sit (or lie down) and observe birds in flight? You’ll probably be as fascinated as you allow yourself to be. With your binoculars, pick out one particular bird in the air and watch for the subtle movements of the wings and tail as the bird changes directions, or watch as the bird takes off or lands. It’s always an impressive performance, and one that’s often taken for granted.

The marvelous adaptation of flight is symbolic of many things, including the freedom of movement, and it fills countless humans with wonder and awe. The ability to fly makes birds one of the most advanced and adaptable of all species. §