Hummingbirds are the jewels of the sky, shining in the sunlight and delighting observers.
The color of hummingbirds appears to change as they move constantly, but do they really change color?
The answer is no. Hummingbirds do not change their colors, but the changing colors that people visualize lie in the physics behind their feathers. Their feathers are iridescent, and that is the cause of the illusion of the apparent color change.
Hummingbirds are sexually dimorphic, and the males are the only ones that have iridescent feathers.
Technically, juvenile hummingbirds change color, but it is not an active choice. Instead, they change color when they mature, and their juvenile feathers are replaced with colorful adult plumage.
Birds’ Feathers: Normal Vs. Iridescent
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Most birds get their feather colors from pigments in their feathers. The pigments are mainly melanin and carotenoids.
The color of the feathers in most birds stays the same throughout their adult lives and does not change color in different lighting conditions.
On the other hand, iridescent feathers are not constricted by the color of the pigments in their feathers. The color that people see is related to the angle of light and the structure of the iridescent feathers.
Hummingbird Feathers
The 300-plus species of hummingbirds have a vast array of different colors that vary in intensity and color with changing angles of light.
One of the most prominent colorful features of male hummingbirds is the gorget.
The gorget is a patch of feathers on the throat and chest of the male hummingbirds. The feathers on the gorget are iridescent, making for a beautiful display of changing colors at different angles.
The Science Behind Iridescence
Sunlight is composed in the form of waves that have a range of wavelengths. The wavelengths determine the visual spectrum of light the human eye can see.
Light waves behave differently with different objects, and the behavior determines the color we observe.
Objects either reflect or absorb light, and the differences in the physics of light cause objects to appear to be colored differently.
The morphology of the hummingbird allows it to utilize a range of wavelengths to make it appear as though it is changing color.
The iridescent feathers contain layers of air bubbles (melanin granules) at the surface. The structure is very different from normal feathers that do not have layers of air bubbles but air bubbles that are scattered instead.
In normal feathers, the light strikes the feather’s surface and gets absorbed only.
The layer of air bubbles causes the light striking the surface to behave in many different ways:
The first way the light can behave is through reflection, whereby the air bubbles will reflect specific wavelengths of light.
Second, specific light wavelengths will pass through the air bubbles and eventually reach the feather’s surface.
Third, wavelengths of a particular length travel through the bubbles and strike the feather’s inner surface.
Lastly, some wavelengths of light only travel through one layer of bubbles and hit the air bubble layer below.
The result of all the ways the light can travel is a combination of reflection and refraction that causes the light to move in various directions – making it seem like the feathers are changing color.
The illusion is caused by changing the angle of the light. The angle of the light that reaches the air bubbles changes with each of the hummingbird’s movements.
That makes the hummingbird appear as though it is rapidly changing color.
Real-Life Example
The ruby-throated hummingbird (Archilochus colubris) has a red gorget under direct sunlight because that is the reflected color. Under different conditions and angles, the shade of red changes and causes a shimmer.
The reflected color is almost black when the sunlight hits the feathers at a flat angle. A slight change in head angle will reflect the color as red again.
Why Do Hummingbirds Have Feathers That Appear To Change Color?
The illusion of color change is not something hummingbirds can control and does not influence other hummingbirds in general.
During the breeding season, vibrant, changing colors come into play.
In the correct amount of sunlight, the changing colors of the iridescent feathers make the display more spectacular to the female.
This may give the hummingbirds an advantage because the female may choose the male with the best colorful display.
Conclusion
Hummingbirds flit about rapidly, changing angles and positions, making it seem like they are changing color. This is an illusion, however. The apparent changing of color is related to the iridescence of their feathers.
In terms of feather colors, the colors are produced by the sunlight reflecting off the feathers and being absorbed. That causes a glistening of colors that changes every instant, making it seem like the feathers are changing color.
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James is a native Texan with a love for birding and outdoor adventures. When he's not birdwatching, you can find him hiking, camping or playing the piano.
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