The Ruby-throated Hummingbird is one of the most common and widespread hummingbird species in North America. The male Ruby-throated Hummingbird has brilliant iridescent red plumage on its throat that can appear ruby-red or even orangey depending on the angle of light. This vibrant throat patch distinguishes the male Ruby-throated from the relatively dull-colored female. But why does the male have such a flashy, colorful throat?
Reasons for the Red Throat
There are a few key reasons behind the striking red coloration of the male Ruby-throated Hummingbird’s throat:
- Attracting mates: The bright, iridescent plumage is thought to play an important role in attracting females during courtship. The flashy throat likely evolved through sexual selection as a way for males to stand out.
- Signaling dominance: The intensity of the red color may signal a male’s health, fitness, and dominance over other males. Older males tend to have brighter, more saturated red throats.
- Camouflage: When not spread in display, the red throat may help camouflage the hummingbird among flowers. The red blends in with the colors of tubular flowers that hummingbirds feed from.
So in short, the Ruby-throated Hummingbird’s red throat mainly functions in mating displays to attract females and assert dominance over other males. The vibrant color results from specialized feather structures as well as carotenoid pigments obtained from the hummingbird’s flower-based diet.
The Iridescent Feather Structure
What makes the Ruby-throated Hummingbird’s throat such a striking red color? The secret lies in the structure of the feathers themselves. The feathers on the throat are highly modified to produce the iridescent, shimmering color.
Iridescence results from microscopic structures on the feather barbules that refract and reflect particular wavelengths of light. In the Ruby-throated Hummingbird, the throat feathers have thin Keratin layers and air bubbles that amplify certain wavelengths in the red part of the visible spectrum when illuminated.
By tilting the feathers at different angles, the hummingbird can maximize the iridescent effect to project the most intense, saturated display of color possible. This ability to finely control the color with small movements of feathers is why the throat can shift between bright ruby red to fiery orange hues.
Carotenoid Pigments
In addition to structural color from the feathers, the rich red iridescence also requires presence of carotenoid pigments. These red and orange plant pigments are acquired through the hummingbird’s nectar diet, especially from flowers of the genus Impatiens.
Carotenoids are integrated into the feather structure and enhance the iridescent effect. The combination of these pigments with the specialized reflective feathers is what allows Ruby-throated Hummingbirds to achieve their brilliant display.
Why the Female Lacks Red Color
In contrast to the flashy male, the female Ruby-throated Hummingbird is relatively drab, with a pale gray throat and greenish back. This results from differences in feather structure and carotenoid accumulation between the sexes.
Without the specialized air bubble architecture, the female’s throat feathers lack the ability to reflect particular wavelengths and produce an iridescent display. The female also consumes less carotenoids than the male, who must acquire enough to continually replenish his bright red throat feathers through molting.
So in short, the plumage differences occur because the female does not need to attract mates or signal dominance. Therefore, the female hummingbird does not have the evolutionary pressures driving her to develop the costly, exaggerated red coloration.
Color Variation
While ruby red is by far the most common color, there is some interesting variation among Ruby-throated Hummingbird males:
- Orange throats – In certain lighting conditions, especially early morning or late day sun, some male Ruby-throated Hummingbird throats can appear orange or orange-red rather than ruby red. This results from subtle differences in carotenoid concentrations and feather structures.
- Albinos – Very rarely, a Ruby-throated Hummingbird is born with genetic leucism that results in a white or very pale throat without pigmentation. However, the underlying feather structure is still iridescent.
- Black-chinned Hummingbirds – In some hybrid zones, Ruby-throateds may interbreed with the western Black-chinned Hummingbird, producing males with vibrant purple throats.
So while ruby red is standard, unusual dietary carotenoids, genetic conditions, and interbreeding can lead to more orange, pinkish, pale, or even purple throat colors on occasion.
Color Over the Year
The Ruby-throated Hummingbird’s throat is brightest when the bird first returns from migration in spring and early summer. After breeding, the throat color may start to fade and look darker later in summer due to feather wear and tear.
Through the annual molt each fall, the hummingbird will replace its throat feathers and regain the vibrant red color to prepare for spring migration and breeding. So early autumn is another period where male Ruby-throated Hummingbirds look their flashing, colorful best.
How the Throat is Used
The male Ruby-throated Hummingbird uses its dazzling red throat in the following ways:
- Courtship Displays – Males flash their throats at females as part of aerial courtship dances to attract mates.
- Dominance – Males will spread their throat feathers towards other invading males in aggressive displays to assert territory and dominance.
- Perching – The throats are conspicuously flashed at females from favored perches in the male’s breeding territory.
Interestingly, some studies have shown that photoreceptors in a Ruby-throated Hummingbird’s eyes are sensitive to the red wavelengths of light reflected from the male’s gorget. This may help the flash of red grab the visual attention of females.
Do Females Prefer Redder Males?
Research has tested whether female Ruby-throated Hummingbirds preferentially mate with males that have redder throats. Results have been somewhat ambiguous:
- Some studies found that females did not demonstrate a preference when given a choice between males with artificially enhanced red throats versus duller unmodified males.
- However, other experiments indicate females do prefer males with brighter, more intense red throats and associate this with higher male fitness.
So female mate preference based on precise throat color remains unclear. Females likely make choices based on a composite of male traits including display behavior as well as throat color.
Red Color as a Health Indicator
The intensity and saturation of the Ruby-throated Hummingbird’s red throat may provide honest clues to the male’s health and condition. Studies have shown:
- Older males tend to have brighter, more iridescent throats than younger males.
- Males with more colorful throats also have higher oxygen-carrying capacity as indicated by red blood cell count.
- Parasitized males have less vibrant, duller throats indicating poorer health.
This suggests the carotenoid pigments and fine structural control required for maximum red throat display carries an honest cost. Healthier, fitter males are best able to develop and maintain the brightest red throats.
A Vivid, Variable Signal
The Ruby-throated Hummingbird’s throat derives its red color from specialized feather structures and carotenoid pigment chemistry. This signal has evolved to provide information on male fitness, dominance, and condition when used in courtship and aggressive displays.
While ruby red is most common, the throat color can shift from orange to purple based on genetics, diet, lighting conditions, and feather wear. This ability to fine-tune the visual signal likely helps males maximize their flashy appeal and communicative power.
Conclusion
In summary, the vibrant red throat of the Ruby-throated Hummingbird male primarily serves to attract mates and deter competitors. Structural color from thin-layered feathers combines with carotenoid pigments from flower nectar to produce an iridescent, satiny gorget. Females seem to prefer males with the brightest, most intense red throats, indicating the male’s health and vitality. So for Ruby-throated Hummingbirds, wearing one’s heart on one’s throat provides an honest, alluring signal of quality and fitness.
