Hummingbirds are some of the most fascinating creatures in the natural world. Known for their speedy flight, hover-feeding, and jewel-toned colors, hummingbirds are a delight to watch. One of the most striking features of some hummingbird species is that the males have brightly colored feathers on their throats, known as a gorget. When male hummingbirds are in courtship displays, these gorgets can appear black, blue, purple, green or red depending on the light. But why does their neck color change from green to red during the mating season? Let’s take a closer look at hummingbird anatomy, courtship behaviors, and evolutionary theories to understand this phenomenon.
Anatomy of Hummingbird Feathers
Hummingbirds actually have two layers of feathers on their throats that can create shifting colors. The top layer contains melanin pigments that appear black, while the underlying layer contains iridescent structural coloration. This structural color results from the way light is reflected off the specialized nanostructures in the feathers. When the feathers are compressed during a display, the iridescent layer becomes exposed, revealing the hidden vibrant colors.
Melanin Layer
The top layer of feathers contains melanin, the same pigment that gives human skin and hair its color. This melanin layer is black, brown, or gray. When the melanin layer lays flat against the bird’s neck, it absorbs much of the iridescent structural color from the lower layer. As a result, we primarily see the darker melanin color when the bird is at rest.
Iridescent Layer
Underneath the melanin feathers is a layer of iridescent feathers. These feathers have highly specialized structures that refract light. The small structures in the feather barbules, called melanosomes, are optimally sized and spaced to interfere with specific wavelengths of light. This interference splits white light into the colors we observe. Even tiny shifts in the positioning of the feathers can change the observed color.
Courtship Displays
During courtship displays, male hummingbirds perform dramatic aerial shows for females. They fly in loops, dives, and rapid ascents to demonstrate their fitness. An important part of these displays involves exposing their colorful throats. They puff up the feathers on their necks to reveal the hidden iridescent layer underneath. The rapid movements also compress and position the feathers optimally to reflect a vibrant display color, often red. The shifting light as the bird moves adds to the dramatic display. By showing off their bright throats, male hummingbirds advertise their quality as a mate to visiting females.
How Neck-Puffing Works
When courting, male hummingbirds alter their neck posture to puff out their feathers. Tiny muscles at the base of each feather allow the birds to control the position and angle of their feathers. To flatten the feathers, the muscle relaxes and elastic ligaments straighten the feather. To puff the plume out, the muscle contracts, overcoming the elastic to tilt the feather outward. With hundreds of feathers puffed in synchrony, a male hummingbird can swiftly transform the entire appearance of his throat for courtship displays.
Behaviors During Courtship
In addition to the neck-puffing, male hummingbirds perform several interesting courtship behaviors:
- Ascending high into the air, up to 130 feet, then diving straight down past the female
- Making u-shaped or j-shaped dives in front of the female
- Flying rapidly back and forth in tight horizontal loops in front of the female
- Hovering in front of the female with the throat puffed out
- Perching close to the female and vocalizing with buzzing, chirping, or scratchy sounds
These behaviors serve to both demonstrate the male’s flight prowess and draw attention to his colorful throat display. Females observe these behaviors when selecting a quality mate.
Why Red? Evolution of Hummingbird Colors
What evolutionary factors drive male hummingbirds to develop brilliant red gorgets for mating? The two main hypotheses are that female choice drives male coloration, and that red signals a male’s quality.
Female Choice
One theory states that the evolution of flashy red throats in male hummingbirds is driven by females preferring to mate with red-colored males. This female choice could be because the females perceive red feathers as more attractive, or because they’ve learned to associate red with higher fitness males. By selecting red-throated mates, female hummingbirds cause the red coloration to become more common over many generations.
Signaling Quality
Another hypothesis is that red gorgets evolved because they act as an honest indicator of male quality. The intense red color may signal a male’s health, strength, and ability to successfully forage. Producing elaborate feathers with highly structured red coloration may depend on the hummingbird’s developmental conditions and available nutrition. By selecting colorful mates, female hummingbirds pass on the genes of healthy males to their offspring. Over time, this drives more males to develop showy red gorgets.
Combination of Factors
In reality, the evolution of hummingbird colors is likely a combination of both female choice for attractive traits and red signaling male fitness. Females both prefer red colors and gain benefits from mating with healthy red-colored males. Together, these factors amplified the spread of red gorgets through sexual selection. Showy ornaments like hummingbird throat feathers evolved because they increase mating success and fertilization.
Changes in Color
The shifting color of hummingbird’s throats is especially noticeable when switching from non-breeding green to brilliant breeding red. Here are some key ways their colors change seasonally:
| Non-breeding (green) | Breeding (red) |
|---|---|
| Melanin layer flattens out | Melanin lifts to expose iridescence |
| Neck muscles relaxed | Neck muscles contracted to puff out |
| Feathers flat and overlapped | Feathers erected and separated |
| Less male competition | Competition for mates high |
| Dull green color | Vibrant red color |
Hormone Regulation
The shift from non-breeding green to brilliant red breeding plumage is triggered by hormones. In the spring, as daylight hours increase, hummingbirds produce more testosterone. This ramps up their mating behaviors and causes anatomical changes like neck-puffing and gorget development. The hormone estrogen also peaks during breeding, which in concert with testosterone triggers the color change. After breeding, testosterone and estrogen levels drop off, causing the gorget to return to the dull green non-breeding coloration. This hormone regulation ensures the colorful throat feathers are only displayed during peak mating time.
Color Variation Between Species
There is interesting variation in throat color and iridescence between different hummingbird species. Here are some examples:
Ruby-throated Hummingbird
The ruby-throated hummingbird, native to Eastern North America, is aptly named for its brilliant scarlet red gorget on the males. The ruby-red throat is iconic and unmistakable during breeding season.
Anna’s Hummingbird
Male Anna’s hummingbirds display rose-pink to magenta throat feathers when breeding. Their color may appear slightly different based on how the light catches the iridescence. Anna’s are common along the Pacific Coast.
Costa’s Hummingbird
The male Costa’s hummingbird has a distinctive purple crown and throat. The violet color results from a mix of refracted red and blue light in the structure of their feathers. Costa’s occur in the Southwestern desert regions of the United States.
Rufous Hummingbird
One of the most dramatic species, the Rufous hummingbird has extensive red plumage extending down its entire neck and belly. The males are bright cinnamon-orange all over their underside. Rufous hummingbirds breed as far north as Alaska.
Differences in Female Plumage
While the males have elaborate breeding coloration, female hummingbirds tend to be more cryptically colored. Their brownish-green feathers provide camouflage while nesting. However, some female hummingbirds may also display some colorful iridescent neck feathers, just not to the same extent as the males. Juveniles of both sexes similarly lack the bright colors until they reach maturity.
Summary: Why Do Hummingbirds’ Necks Turn Red?
In summary, male hummingbirds have evolved showy red and iridescent throat feathers through sexual selection as both a colorful ornament to attract mates and a signal of fitness to potential partners. By puffing out their neck feathers, male hummingbirds can quickly switch their throats from dull green to flashy breeding season red. Hormones trigger this color change and related mating behaviors. The vibrant red throat helps the male successfully court females and transmit his quality genes to offspring. While the different species have unique colors, red gorgets in particular stand out as serving an important role in hummingbird reproduction and evolution.
