Wingtip Feathers Increase Aerodynamic Efficiency

a brown eagle with a large wingspan flies over dark green trees

Biological Strategy

Birds

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Image: Klappe / Pixabay / Free non-commercial use

Optimize Shape/Materials

Resources are limited and the simple act of retaining them requires resources, especially energy. Living systems must constantly balance the value of resources obtained with the costs of resources expended; failure to do so can result in death or prevent reproduction. Living systems therefore optimize, rather than maximize, resource use. Optimizing shape ultimately optimizes materials and energy. An example of such optimization can be seen in the dolphin’s body shape. It’s streamlined to reduce drag in the water due to an optimal ratio of length to diameter, as well as features on its surface that lie flat, reducing turbulence.

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Modify Buoyancy

Buoyancy is an upward force exerted by air or liquid on a solid object that works against the object’s weight. A hawk glides through air and a duck floats on water due to buoyancy. Some living systems (such as fish eggs) can remain sedentary and therefore maintain the same buoyancy at all times. But most must adjust their buoyancy because they can’t survive long unless they change position. These living systems require strategies to not only be buoyant, but also adjust buoyancy level. They often modify buoyancy by adding or decreasing lift, or by changing their weight. For example, birds like condors that soar for a long time shift the directional orientation of their wingtip feathers to manage buoyancy. Fish alter the amount of air in their swim bladders to increase or decrease their weight, thus altering their buoyancy.

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Protect From Wind

Wind subjects living systems to various forces, such as compression, twisting, turbulence, and tension. These forces put living systems at risk of losing the ability to perform life-essential functions, such as when a plant becomes uprooted. Wind can result from weather phenomena or rapid movement through the air, as when flying. Wind is typically not a constant or predictable force, so living systems must be able to function both with and without its presence by adjusting to its direction and speed. A good example is how plants’ leaves and stems are flexible so that they can align with the wind, rather than being battered by it.

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Move in/Through Gases

Living systems must move through gases (which are less dense than liquids and solids) such as those in the earth’s atmosphere. The greatest challenge of moving in gases is that because the living system is heavier than the gas, it must overcome the force of gravity. Moving efficiently in this light medium presents unique challenges and opportunities for living systems. As a result, they have evolved countless solutions to optimize drag and increase lift so that they can stay aloft and take advantage of variable currents. Additionally, they must overcome gravity when moving from a liquid or solid into the air. The fairyfly, the smallest known insect, is a tiny wasp that must move through the air. To the wasp, air feels like a heavy liquid and to move through it, it uses special feathery oars rather than wings.

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Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

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Wingtip feathers in birds are aerodynamically efficient because of their torsional flexibility.

Image: devilarts (Snick Spy) /

The three birds are shown in different types of flight. The middle bird is in the downstroke, and its primary flight feathers are positioned to get the full lift. The bird on the left is starting to lift its wings after the downstroke, and the feathers are positioned to decrease resistance. The bird on the right is near the top of the stroke, and its feathers are positioned similar to the one on the left, but about to twist for the downstroke.

Image: Alan D. Wilson /

Northern Hawk Owl , Pincourt, Near Montreal, Quebec. 2010.

Image: Alan D. Wilson /

Bald Eagle, Morris Valley Road, Harrison Mills, British Columbia. 2008.

Image: Alan D. Wilson /

Roseate Spoonbill, Birding Center, Port Aransas, Texas

Image: Adrian Pingstone / wikipedia /

Wing tip devices displayed on this Bombardier Learjet are designed after the wing tips of birds such as eagles

“Nature, by contrast, takes a less disdainful attitude toward torsion–in some applications adequate resistance matters, but in many others function depends on having sufficient torsional flexibility. A bird’s wingtip feathers must twist in one direction during the upstroke of the wings and in the other direction during the downstroke to keep the local wind striking the wing at an appropriate angle to generate lift and thrust…The turning could be done at the base, with a completely inflexible feather; the aerodynamics are improved and material saved if the local flow forces twist the feather by just the right amount.” (Vogel 2003:382)

Last Updated October 25, 2016

References

Book

Comparative Biomechanics: Life's Physical World, Second Edition

17/06/2013 | Steven Vogel

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