Hummingbirds are known for their ability to hover in midair and for their iridescent plumage that shimmers in the light. While most hummingbird species have a set plumage color, there is one group of hummingbirds that can actively change the color of their feathers: the mountain gems.
Mountain gems are a group of hummingbird species found in the Andes mountains of South America. They belong to the genus Oreotrochilus and are sometimes referred to as “hillstars”. There are around 5-6 species of mountain gems, with the most well-known being the Andean hillstar (Oreotrochilus estella) and the black-breasted hillstar (Oreotrochilus melanogaster).
| Species | Distribution |
|---|---|
| Andean hillstar (Oreotrochilus estella) | Colombia, Ecuador, Peru, Bolivia |
| Black-breasted hillstar (Oreotrochilus melanogaster) | Peru |
| Green-headed hillstar (Oreotrochilus stolzmanni) | Peru |
| Giant hummingbird (Oreotrochilus chimborazo) | Ecaudor |
| Wedge-tailed hillstar (Oreotrochilus adela) | Bolivia, Argentina |
So what allows these mountain gems to change their colors? The secret lies in their feathers.
Iridescent Feathers
Like all hummingbirds, mountain gems have iridescent plumage that appears to change colors when viewed from different angles. This iridescence is created by specialized feather structures. Hummingbird feathers have thin, flattened barbules that are arranged like shingles on a roof. These barbules contain plate-like melanosomes that are filled with the pigment melanin.
When light hits the feathers, the melanosomes split the light beams through diffraction and interference. As the viewing angle changes, different wavelengths are reflected back, showing different colors. This allows hummingbird feathers to flash between fiery reds, greens, and blues.
| Color | Wavelengths |
|---|---|
| Red | 700-635 nm |
| Orange | 635-590 nm |
| Yellow | 590-565 nm |
| Green | 565-500 nm |
| Blue | 500-450 nm |
| Violet | 450-400 nm |
This type of iridescence based on melanin is called structural coloration. It’s what gives peacock feathers and butterfly wings their shimmering hues too. But mountain gems have an additional layer of color change ability beyond this structural iridescence.
Dynamic Color Change
What sets mountain gems apart from other hummingbirds is their ability to dynamically alter the orientation of the melanosomes in their feathers. Within seconds, they can actively change the alignment of the melanosomes to display different colors.
Researchers have found that this color shifting ability is triggered by changes in physiology. By contracting special muscles around the follicles of growing feathers, mountain gems can apply pressure that rearranges the interior structures.
Studies show that when the birds are calm, their feathers lay flat, structurally reflecting mostly yellows and greens. But when excited or aggressive, the mountain gems can flex their follicles to shift the melanosomes into a more disorderly alignment. This makes the feathers reflect vibrant reddish hues.
| Feather state | Color |
|---|---|
| Relaxed | Green/yellow |
| Excited | Red/orange |
Researchers believe mountain gems use this rapid color shifting to communicate and signal dominance during aggressive encounters. The vivid shift from green to red is clearly visible to other birds. By flaring their feathers, mountain gems can flash bright warnings and declare their strength.
Species Differences
While all mountain gems have dynamic color change abilities, the specifics differ somewhat between species. Here are some key differences:
Andean Hillstar
The Andean hillstar shows the most dramatic color shifts. When calm, its feathers appear bright green. But it can swiftly shift to burning red-orange plumage when aggressive. Males and females have similar color-change abilities.
Black-breasted Hillstar
As its name suggests, the male black-breasted hillstar has a distinctive black chest band. Its relaxed state is mostly green, while aggressive displays feature vivid red crown feathers. Females lack the black breast band and have more muted color shifts.
Green-headed Hillstar
This species has an olive-green head and upper chest. It is less studied, but is believed to have color-changing abilities similar to other hillstars. The intensity of color shifts may be more subtle compared to the Andean hillstar.
Giant Hummingbird
Despite its name, the giant hummingbird has more muted color-changing abilities. Its feathers may show a slight shift from yellow-green to red when excited, but the effect is much less dramatic.
Wedge-tailed Hillstar
The Wedge-tailed hillstar is the least studied member of the mountain gems. But limited observations indicate it likely has dynamic color-changing feathers like its relatives. The specifics of its color shifts remain unknown.
Conclusion
In summary, mountain gems are the only hummingbirds able to alter their plumage colors by actively manipulating their iridescent feathers. While other hummingbirds have static structural color from their feathers, mountain gems can swiftly change their alignment to flash different hues. Researchers believe this helps the birds communicate and signal aggression. Among the mountain gems, the Andean hillstar shows the most intense color-shifting abilities. So if you’re looking for a hummingbird that can swiftly change its colors, keep an eye out for the fiery feathers of the remarkable mountain gems!
