Anna’s hummingbird (Calypte anna) is a small hummingbird found along the west coast of North America. The male Anna’s hummingbird has iridescent plumage on its head and throat that can appear red, pink, orange, and green depending on the angle of the light. This has led to some speculation that the Anna’s hummingbird can actively change the color of its feathers. In this article, we’ll explore what’s really going on with the Anna’s hummingbird’s shifting colors and discuss whether it can actually change the color of its feathers on command.
Do Anna’s Hummingbird Feathers Physically Change Color?
The short answer is no – the feathers of the Anna’s hummingbird do not physically change color. The color shifts we see are caused by structural coloration, not by changes to the actual pigmentation of the feathers. Structural coloration relies on microscopic structures on the surface of the feathers that interfere with light waves to produce certain colors. These structures are fixed and cannot be altered by the bird.
Specifically, the feathers of an Anna’s hummingbird contain melanosomes – tiny granules of the pigment melanin. The melanosomes are packed into disk-like platelet structures. These platelet stacks are very small, around 400 nanometers thick. Their scale is similar to the wavelengths of visible light, which allows them to disrupt selected wavelengths through interference effects. This is what produces the iridescent, rainbow-like colors.
The spacing and orientation of the melanosomes differ between feathers. As the bird moves, the plates catch the light at different angles, resulting in variable color patterns. So the color change is an optical illusion – the structures themselves don’t change or move. It’s simply due to the interaction between the nanostructures in the feathers and the viewing angle.
How Do Other Birds Achieve Color-Changing Plumage?
While Anna’s hummingbirds can’t actively alter their colors, some other birds can! Here are a few examples of birds that use other mechanisms to change their plumage color on command:
- Pinyon jay – Has special feathers containing a yellow pigment called phaeomelanin. By dispersing the pigment into the feather tips, the jay can transform its crown from blue to yellow.
- Vermilion flycatcher – Can ruffle special reddish feathers on its crown to conceal or reveal them, essentially “turning on” a red crown.
- Western tanager – Has yellow feathers on its head/body. During molting, it can absorb the yellow pigment to reveal an orange-red color underneath.
So while Anna’s hummingbirds rely purely on structural color from nanostructures, other birds actively control pigment dispersal and feather movement to generate changeable plumage.
Why Does the Male Anna’s Hummingbird Have Iridescent Feathers?
Displaying flashy iridescent feathers likely evolved in male Anna’s hummingbirds because it helps them attract mates and compete with rival males.
Some key reasons their vibrant plumage is beneficial:
- Helps impress females during courtship
- Intimidates competing males when defending territory
- Camouflage – their shifting colors blend into vegetation in the hummingbird’s habitat
- The iridescence signals good health and vitality to potential mates
Additionally, the shimmery throat feathers likely coevolved with the Anna’s hummingbird’s elaborate diving courtship displays. By flashing their iridescent throat patches during these maneuvers, they can better catch the female’s attention.
How Do Anna’s Hummingbirds Produce Color Without Pigment?
Anna’s hummingbirds rely on structural coloration rather than pigments to produce their shifting iridescent colors. As mentioned earlier, this involves microscopic structures that interfere with light waves.
Here’s a closer look at how it works:
- Their feathers contain melanin granules called melanosomes stacked into disk-shaped plates
- The stacks are around 400 nanometers thick – similar to the wavelengths of light
- When light strikes the plates, some wavelengths are reflected while others pass through
- The reflected wavelengths produce the color we observe
- Slight changes in the spacing and orientation of plates alters the reflected color
This mechanism allows Anna’s hummingbirds to generate vibrant colors using only a single pigment – melanin. By precisely controlling melanosome density and plate characteristics, they can fine-tune the desired hues.
How Does Iridescence Help Anna’s Hummingbird Survival?
The iridescent plumage of male Anna’s hummingbirds provides several key survival benefits:
- Camouflage – Their shifting colors allow them to blend into the surroundings. The bronzy-green hue matches vegetation.
- Thermoregulation – The dark iridescent feathers help absorb heat from sunlight.
- Sexual selection – Iridescence signals health and helps attract mates.
- Territory defense – Flashy colors help scare away competing males.
Additionally, the flexibility of the colors allows each male to produce unique patterns as an additional level of identification. The iridescence provides camouflage from predators when still, while enabling sexual displays when moving.
What Triggers Color Change in Anna’s Hummingbird Feathers?
Anna’s hummingbirds do not actually change the color of their feathers. However, their iridescent throat feathers appear to rapidly shift between different hues of red, pink, orange, and green.
These striking color fluctuations are caused by changes in the angle at which light hits the tiny melanin-containing platelet structures in the feathers. Even slight movements alter the interference of light waves on the plates, producing different colors.
When the bird moves its body and feathers while flying or maneuvering, the small variations in the orientation of the plates relative to your eye will drastically change the perceived color. The feathers themselves remain unchanged.
This allows Anna’s hummingbirds to “flash” different colors without actively altering their plumage. The rapid color shifts are useful for communication during courtship displays or aggression toward other males.
How Many Feathers Does an Anna’s Hummingbird Have?
Anna’s hummingbirds have approximately 1,000 feathers covering their entire body. This includes:
- About 940 feathers on the body (contour feathers)
- Around 60 feathers on the wings and tail (flight feathers)
The most important feather areas creating the iridescent colors are:
- The gorget (throat patch) – this area contains specialized iridescent feathers
- The crown on the head
Females also have iridescent gorget feathers, but they are significantly smaller and less vibrantly colored than in males. The females instead have more cryptic brownish-gray plumage on their head and body.
The feathers are essential for the hummingbird’s survival, providing:
- Thermoregulation
- Protection from wind and rain
- Camouflage from predators
- Colorful sexual displays
Do Anna’s Hummingbird Molt Their Feathers?
Yes, Anna’s hummingbirds molt their feathers once per year after the breeding season. Molting replaces old, worn out feathers with newer plumage.
The molt cycle includes:
- Late summer molt of body feathers and some wing feathers
- Fall/winter molt of the remaining wing feathers
- Late winter molt of the iridescent throat feathers
This staggered approach prevents the bird from becoming flightless. The colorful male gorget feathers regrow in time for the breeding season.
Females may have a second minor molt before breeding to renew their less flashy throat feathers. The new plumage signals their readiness for mating.
Molting is energetically expensive, so the birds need adequate food resources during the process. It is one of the most dangerous times in the hummingbird’s life.
Do Anna’s Hummingbird Nestlings Have Adult Plumage?
No, Anna’s hummingbird nestlings do not have full adult plumage initially. Their feathers develop gradually:
- Hatchlings only have down feathers for warmth and protection
- The first true feathers emerge around 2 weeks after hatching
- Juveniles leave the nest at 3 weeks but lack the full adult plumage
- The iridescent throat feathers don’t grow until first molt at around 1 year old
Male Anna’s hummingbird nestlings may show some scattered iridescent feathers, but never a full vibrant gorget like the adults. The duller feathers help the fledglings blend into their surroundings.
Interestingly, some males develop a dark throat with no iridescence in their first year before molting into the colorful adult plumage.
Do Other Birds Have Iridescent Feathers Like the Anna’s Hummingbird?
Yes, iridescent structural coloration is common in other birds besides Anna’s hummingbirds. Some examples include:
| Bird | Area of Iridescence |
|---|---|
| Peacock | Tail feathers |
| Magpies | Wings, body |
| Kingfishers | Chest, throat |
| Starlings | Throat, wings |
| Pigeons | Neck feathers |
The nanostructures producing iridescence may differ, creating unique effects. Oil droplets in peacock tail feathers create their shimmering “eyespot” patterns.
But in all cases, the mechanism involves interference of light rather than pigments. This allows a single melanin source to generate diverse, changeable colors.
Do the Iridescent Feathers Change Over the Anna’s Hummingbird’s Lifespan?
Yes, the iridescent gorget feathers of male Anna’s hummingbirds do change over the bird’s lifespan.
Young fledglings lack a colorful throat patch. The vibrant gorget first develops during the first molt at around 1 year old.
Adult males then replace their gorget feathers through molting each winter. The new feathers may vary slightly from previous years.
Over time, the total gorget area tends to increase. Older males have larger throat patches with more iridescent feathers.
Additionally, the hues may shift subtly with age, reflecting feather nanostructure changes.
Females also regrow small iridescent throat patches each winter, preparing for the breeding display rituals.
Conclusion
In summary, the brilliant plumage of male Anna’s hummingbirds appears to rapidly change colors. However, this is an optical illusion. Their iridescent feathers have fixed nanostructures that passively produce shifting colors when viewed from different angles.
While the hummingbirds can control their feather orientation through movement, they cannot actively alter the feather pigmentation or structure itself. So an Anna’s hummingbird’s feathers do not physically change color, remaining structurally constant until the yearly molt.
The combination of small melanin-containing platelets and flexibility in feather positioning allows Anna’s hummingbirds to flash elaborate, vivid colors. This offers camouflage while also attracting mates and deterring rivals.
So next time you see an Anna’s hummingbird in the sun, watch closely as its throat seems to flash in rainbow hues. But remember – it’s not actually changing its feathers’ true colors! The magic is happening at the microscopic level through physics, not biology.
