Quick Answers
There are a few key factors that determine the vibrant colors of hummingbirds:
- Feather structure – The microscopic structure of hummingbird feathers reflects light to produce iridescent colors.
- Pigments – Carotenoid and melanin pigments in feathers also contribute to color.
- Diffraction – Thin-film diffraction from the layered structure of feather barbules creates additional colors.
- Diet – Carotenoid pigments come from the birds’ diet of nectar and insects.
- Genetics – Genes control how pigments are distributed in feathers.
So in summary, it is the combination of structural feather characteristics and pigment use, influenced by diet and genetics, that creates the vibrant plumage of hummingbirds. The interplay of these factors produces the metallic, shimmering colors we see in these tiny birds.
Feather Structure
The microscopic structure of hummingbird feathers is one of the main factors that creates the iridescent, glistening colors. Here’s how their feather structure contributes to color:
- Thin overlapping layers – Hummingbird feathers have thin layers of keratin that overlap. These layers reflect light at different angles.
- Melanosomes – These small packets of melanin pigment in feather barbules also affect light reflection.
- Air pockets – Small air pockets in the feather barbules also influence the reflection and refraction of light.
As light hits these complex microscopic structures in the feathers, some wavelengths are reflected while others are absorbed. This selective reflection of specific colors is what produces the iridescent, metallic sheens we see.
For example, in Anna’s hummingbird, the males have feather “gorgets” on their throat that appear reddish. This is produced by layered structures in the feathers reflecting red and orange light back to the viewer. The shape of melanosomes and air pockets in the feathers determine exactly which colors are reflected.
Examples of feather structures creating color
| Hummingbird Species | Feather Structure | Colors Produced |
|---|---|---|
| Anna’s Hummingbird | Thin stacked plates on throat feathers | Iridescent red and orange |
| Costa’s Hummingbird | Elongated melanosomes in crown | Iridescent violet and magenta |
| Rufous Hummingbird | Thick melanosomes in throat feathers | Iridescent orange and green |
As you can see, subtle differences in nanostructure can refract light in different ways, producing the signature colors of each hummingbird species. The shape, thickness and layering of melanosomes and keratin determine the colors we observe.
Pigments
In addition to structural colors from feather anatomy, hummingbirds also utilize pigments to add color to their plumage. The two main types of pigments are:
Carotenoid pigments
These pigments produce red, orange and yellow colors. Hummingbirds acquire carotenoids from their diet of flower nectar and small insects. Depending on the types of carotenoids present in their habitat, the carotenoid-based colors of feathers can range from yellow to deep red.
Melanin pigments
Melanins produce darker black, brown and rusty-red hues in feathers. Melanin is produced directly by the bird and is not obtained through the diet. The two forms of melanin that contribute to feather color are:
- Eumelanin – Produces black and dark grey colors.
- Phaeomelanin – Produces reddish-brown and chestnut hues.
In addition to producing dark pigment colors, melanin in structures called melanosomes also contributes to iridescent structural color (as discussed earlier). The shape and arrangement of melanosomes influences light reflection and refraction.
The combination of structural color mixing with carotenoid and melanin pigments allows hummingbirds to produce a spectacular variety of plumage colors. The balance of these pigments is controlled by genetics and diet.
Diffraction
A less well-known contributor to hummingbird feather color is a phenomenon called thin-film diffraction. This occurs when light hits extremely thin layers of material and is diffracted into specific colors.
In hummingbird feathers, the layered structure of the barbules creates nanoscale films just hundreds of atoms thick. When light hits these layers, constructive and destructive interference patterns are created based on the thickness and regularity of the layers.
As a result, specific colors are reflected back. Even tiny variations in the thickness of these layered structures can shift the color. This thin-film diffraction adds an extra dash of color to the feather structural and pigmentary colors already present.
Dietary Influence on Colors
As mentioned already, hummingbirds get their colorful carotenoid pigments from the foods they eat. Therefore, their diet has a significant influence on plumage coloration.
Here are some examples of how diet impacts color:
- In the wild, hummingbirds get carotenoids from flower nectar and eaten insects. These contribute to vibrant reds and oranges in their feathers.
- Captive hummingbirds fed plain white sugar water will have less colorful plumage over time as they obtain fewer carotenoids.
- Certain flower species provide unique carotenoids. For example, hummingbirds feeding on honeysuckles display hot pink throat feathers.
- Molt periods require extra sources of carotenoids from the diet to renew brightly colored feathers.
The availability of colorful carotenoid pigments in the habitat shapes the specific plumage colors that develop in each hummingbird species.
Genetic Control of Colors
The final contributor to hummingbird colors is genetics. Genes provide the blueprint for how pigments are deposited into the birds’ developing feathers.
Specific genes control:
- How much of the different carotenoid pigments are integrated into feathers.
- The specific melanin patterning in feathers.
- The shape and structure of melanosomes that influence iridescence.
- The precise nanostructure and layering of feathers that refracts light.
Hummingbird species have evolved different versions of these genes over time. This allows each species to have a unique genetic “recipe” for its colorful feathers, even when eating the same diet.
Additionally, hummingbirds may have genes for producing certain pigments but not express them in their phenotype. For example, the red iridescent gorget of Anna’s hummingbird is only expressed in adult males, controlled by gene expression specific to age and sex.
Ultimately, evolution has tuned hummingbird genetics over millennia to take advantage of structural colors, pigmentary colors, and iridescence. The result is the shimmering beauty we observe in these tiny flying jewels of nature.
Conclusion
In summary, hummingbird feather color is determined by:
- Structural color from the microarchitecture of feathers
- Carotenoid and melanin pigments acquired through diet and genetics
- Thin-film diffraction from nanolayers in feathers
- Genetic control over color production and patterning
The interaction of these factors allows hummingbirds to produce a stunning palette of reds, greens, blues, purples, and everything in between. The iridescent blending and shading of colors is mesmerizing and unique in the animal kingdom. We now understand the optical and biological factors that make hummingbird colors possible, yet they remain a gorgeous and captivating natural wonder.
