Icarus Envy: Wings

It’s cold outside! The dark-eyed juncos shelter on the porch when they’re not cleaning up under the bird feeder. They flap and flutter in consternation and fly away when I step out on the porch. Out there in the quiet day, sparrows and chickadees send their occasional calls into the winter air. They flit from tree to tree looking for food. Perhaps they’ll take a chance on the bird feeder if the coast is clear. If the cardinals or downy woodpeckers are around, they’ll look elsewhere.

Flying birds are, of course, just a common feature of the landscape at Owl Acres. But I still marvel at their effortless flight, doing what I as a human can never do except in my dreams.

People have been dreaming about flying long before me. Icarus with his wings and beeswax that worked until he flew too close to the sun; Leonardo da Vinci and his plans for a helicopter; the Wright Brothers who counted only a few seconds of flight as success. How marvelous it would be to launch into the air like a bird and ride the air currents, or even just to flap in undulating flight from tree to tree.

Why flight evolved in birds is a topic of discussion among people who study such things. Whatever the reason, the fact remains that birds have evolved to fly and do it very well. But how?

Dr. LaPrice has me thinking about bones, so we’ll start there. Birds are vertebrates. They have a skeleton comprising a skull, a backbone and ribs like other vertebrates. In order to fly, those bones need to be as light as possible. Therefore, instead of the solid heavy bones of mammals, birds have delicate bones with air pockets incorporated into their structure to make them lighter. They have also fused some of their bones to reduce weight. Songbirds like the white-breasted nuthatch and the white-throated sparrow weigh less than an ounce, and the chickadees and dark-eyed juncos weigh as little as half an ounce.

Birds are actually quadrupeds, with four limbs like us—2 legs and two arms or wings. A bird’s wing has the same bones as my arm. You can see them when you finish your hot wings. It has a Humerus, comparable to my upper arm; the radius and ulna, those two parallel bones that comprise my forearm, and a “hand” with three little fingers at its tip. The “hand bones” have fused into a stronger structure, and the “finger bones” have also fused from five to three. With its fingers, the bird can control its primary flight feathers, changing the angles and spreading them out or holding them closer together. Muscles in Its “forearm” control the secondary flight feathers, shaping them into the air foil needed to support flight. The humerus or upper arm bone connects to strong muscles in the breast, where the flapping and flying happen.

Of course, all birds are not exactly alike. They live in various environments and have different needs. Their wings have evolved with this in mind. Ornithologists categorize bird wings into five groups—active soaring; passive soaring; high-speed wings; elliptical wings; and hovering wings.

Wings designed for active soaring are along and narrow like airplane wings. Birds with this type of wing tend to be seabirds that fly vast distances over the ocean like gulls or albatrosses. Strong constant winds carry the birds along with minimal expenditure of energy. This wing shape is also advantageous for very slow flight or in some cases hovering. Like an airplane, birds with these long narrow wings require a long taxi to get off the ground.

Passive soaring is how ornithologists describe the wings of buzzards, eagles, and some hawks. This style is shorter and broader than the active soaring wing. They also have long, broad primary flight feathers attached to their fingers which can be organized into a series of slots at the tips of the wings. This configuration minimizes drag at the tips of the wings, therefore requiring less energy to fly. They are also conducive to soaring, riding on updrafts. Canada geese, for instance, have to run and flap madly to get off the ground, but once they’re up there, they can fly for hours and thousands of miles with minimal energy expended in flapping their wings.

A third category of wing shape is high-speed wings. These wings are shorter than the soaring wings, and pointed. Examples include barn swallows and starlings. They can fly up to 45 miles per hour and are highly maneuverable, catching insects on the wing.

Probably the most common shape of wing that we see on Owl Acres is the elliptical wing. Our little chickadees and finches aren’t planning to fly to Mexico. They just need to take off quickly to avoid predators and fly around home. Flapping their elliptical wings gives them a lot of lift to get off the ground. This wing shape also gives the birds maneuverability in forests and woods. The short, rounded wings of the much larger wild turkey also offer explosive ascents from the ground and brief, rapid flight. This requires a large expenditure of energy and isn’t suitable for long distances, but the turkeys don’t migrate, so it works for them.

The ruby-throated hummingbird is unusual in the bird world because it can hover whereas most birds need forward momentum to stay airborne. To achieve this feat, the hummingbird flaps its relatively long, narrow wings up to 80 times per second, rotating the wing at the shoulder and elbow in a figure eight movement. This gives them lift on both the upstroke and the downstroke, keeping them in the air.

Each species has evolved to meet the needs of its habits and environment. Variations among and within the various types of wings create finely honed flying machines. So there they go, flying around like it’s no big deal.

Feature image attribution: Alithographica.com Art and Scientific Illustrations by Jenn Deutscher Alt text: 5 Bird Wing Types as described in the text. Each wing type equips the bird for its specialized flight regime e.g. soaring, maneuvering, fast flight, hovering etc.