How Do Birds Fly?
- Nikhil Patel
- 1 day ago
- 2 min read
Before the Wright brothers first flew a powered, heavier-than-air aeroplane in the skies on 17 December 1903, humans believed that flying would have to work the same way it does for birds—by flapping wings. For centuries before that moment, men tried to attach wings to their arms, only to realize that the wings were too heavy and that the human body does not have strong enough chest muscles to flap such large wings fast enough to generate lift. Birds, on the other hand...
Bird’s Anatomy
Light, hollow bones: Birds’ bones are hollow, very thin, and extremely lightweight. For example, a frigatebird with a 7-foot wingspan weighs only about 115 grams in its wing bones.
Extremely light feathers: Feathers make up barely 6% of a bird’s total body weight. A dove has around 25,000 feathers and yet it weighs remarkably little.
Powerful flight muscles: The muscles that flap the wings are the strongest in a bird’s body. About 25%–35% of the bird’s total weight is concentrated in these chest muscles.
A body built to be light: To keep their weight low, birds lack many heavy body parts found in other animals. They have no heavy legs for walking, no teeth, no urinary bladder to store urine, no full-sized lungs, and relatively small intestines. All of this makes their bodies light enough to be lifted into the air.
How Do Birds Fly?
When birds push their wings downward during the downstroke, they push air downward. According to Newton’s Third Law of Motion (for every action, there is an equal and opposite reaction), this downward push of air creates an upward force that lifts the bird into the sky.
When birds bring their wings back up for the next stroke, they do not keep them flat. Instead, they bend and slightly fold them, opening small gaps between the feathers so that air can pass through easily, reducing resistance.
The shape of a bird’s body is also designed to be highly aerodynamic, which reduces friction with the air. The body is relatively flat underneath, so air pressure remains more uniform. Because of this efficient design, birds do not need to flap their wings constantly.
Fun Fact
Some birds can sleep while flying. Species such as frigatebirds are able to rest one half of their brain at a time, allowing them to stay in the air for days without landing.
References
Gill, F. B. (2007). Ornithology (3rd ed.). W. H. Freeman. https://global.oup.com/academic/product/ornithology-9780716749837
National Audubon Society. (n.d.). Bird anatomy and flight. Retrieved June 21, 2026, from https://www.audubon.org
Smithsonian National Air and Space Museum. (n.d.). How things fly: Bird flight. Retrieved June 21, 2026, from https://howthingsfly.si.edu
Rattenborg, N. C., Voirin, B., Cruz, S. M., Tisdale, R., Dell'Omo, G., Lipp, H. P., Wikelski, M., & Vyssotski, A. L. (2016). Evidence that birds sleep in mid-flight. Nature Communications, 7, 12468. https://doi.org/10.1038/ncomms12468
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