Great egrets are elegant, white wading birds found near water throughout much of the world. During the breeding season, great egrets develop colorful plumes used for courtship displays. The breeding plumes of great egrets are quite spectacular, featuring long, lacy feathers in shades of green, blue, and reddish-pink. While their bright white plumage remains throughout the year, these colorful breeding plumes only appear for a few months each spring.
Appearance of Great Egrets
Great egrets (Ardea alba) are fairly large wading birds, standing around 3 feet tall with a wingspan of around 5 feet. Their most distinctive feature is their bright white plumage which covers their entire body. This white coloration extends to their long, straight bill and legs as well. Great egrets have a sloping neck, black legs and bill, and yellow feet.
During breeding season, great egrets develop specialized plumes called aigrettes on their shoulders, lower back, and chest. These plumes can reach up to 30 inches long. While the body feathers remain white, the aigrettes take on brilliant colors. The aigrette feathers feature fluffy white bases that transition into green, blue, pink, reddish and bronze hues. The colors appear brighter and more vibrant closer to the tips. When displayed during courtship rituals, these aigrette plumes create a spectacle of color.
Breeding Plumage Colors
The breeding plumage and aigrette feathers of great egrets display the following range of colors:
Greens
Great egret aigrettes can display bright emerald greens, sea greens, light minty greens, dark forest greens, and even yellow-greens. The green iridescent hue comes from refracting light through the molecular structure of the feathers. The shade of green depends on the precise structural arrangement of the feather barbs and barbules. Slight variations in angles and lengths produce different wavelengths of light and green colors.
Blues
A range of rich blues can also appear in great egret breeding feathers. Deep royal blues, light sky blues, turquoise, aquamarine, and sapphire shades are all possible. As with the green hues, the specific blue color depends on the structural mechanisms within the feather that reflect blue wavelengths of light.
Pinks
Great egrets can display pinkish plumage ranging from soft peach to deep magenta. The pinks include rosy pink, hot pink, and reddish-purple pinks. Structural variations allow the feathers to refract and reflect light in the red spectra.
Bronze
Some great egret aigrette feathers also take on a dark bronze or cinnamon hue. The bronze color results from light reflecting off melanin pigment granules contained within the plumage barbules. The concentration of melanin determines the intensity of the bronze color.
Changes Outside of Breeding Season
Great egrets lose their nuptial plumes immediately following the breeding season in the spring. The aigrettes fade quickly once eggs are laid and chicks hatch. By early summer, great egrets revert back to basic white plumage.
The aigrette plumes begin growing again by autumn in preparation for the next breeding season. Peak breeding in North America occurs February to April. Further south, great egrets may breed at any time of year in response to weather patterns and food availability.
By winter, the plumes are fully developed again for courtship rituals. The breeding colors are maintained until late spring when nesting commences. This seasonal shift in plumage follows an annual cycle linked to breeding activities.
Display of Breeding Plumage
Male great egrets use their vibrant breeding plumage to attract females and establish dominance. During courtship displays, males will spread their plumes, stretch their neck, bob their head, and fence with other males. The displays also help maintain pair bonding between mated birds.
Females assess potential mates based on the brilliance of their breeding plumage. Males with the brightest and most colorful plumes tend to gain more mating opportunities. The plumes signal the male’s fitness and quality as a mate.
Great egrets nest in large colonies containing up to several thousand pairs. This environment provides ample opportunities for males to show off breeding plumage and compete for females. The displays also allow comparison between many males simultaneously.
Purpose of Vibrant Breeding Colors
Ornithologists have proposed several evolutionary theories for why great egrets have developed such brightly colored breeding plumage:
Sexual Selection
The colors help attract females and give an advantage in reproduction. Brighter plumes indicate better health and genes. Females gain indirect benefits by selecting colorful males to pass qualities to offspring.
Social Selection
The plumes establish dominance and improve ability to compete with other males at crowded breeding colonies. Males with brighter colors tend to obtain better nesting sites and more mates.
Species Recognition
The unique breeding colors may help great egrets identify their own species and select appropriate mates at mixed colony sites shared with other egret species.
Predator Avoidance
The striking appearance may startle potential predators when great egrets are at vulnerable nests. The bold colors could send a warning signal.
Differences Between Males and Females
Both male and female great egrets develop breeding plumes, but males grow longer and brighter colored feathers. Females still exhibit the green, blue, bronze and pinkish aigrettes during courtship, but their colors tend to be paler and less vibrant.
On average, male aigrettes reach 20-30 inches long compared to just 10-15 inches for females. The magnification of male ornamentation follows the principles of sexual selection, as females favor more flamboyant displays.
Apart from plume differences, males and females are identical in size and coloration. They are sexually monomorphic and cannot be distinguished outside of the breeding colors. Even juvenile birds resemble adults.
Regional Variations
Interestingly, great egrets display subtle geographical variations in breeding plumes across their widespread global range:
Old World vs New World
Great egrets native to Europe, Asia and Africa (the Old World) tend to have greener plumes on average compared to the blues and pinks of American birds. However, significant overlap occurs.
Southern Populations
Birds from tropical regions like Florida and the Caribbean exhibit longer, lusher plumes on average than northern temperate populations. The intensity of colors also increases southerly.
Pacific Coast
West coast great egrets show a higher proportion of blue in plumes compared to more bronze and pink along the Atlantic coast. Regional food sources may influence feather pigments.
Australia
The smallest and palest breeding plumes occur in Australian great egrets. This may be an adaptation to hot, dry conditions. Darker feathers absorb more heat.
Despite these subtle geographic shifts in hue, great egrets from all regions retain multipurpose colors used in mating rituals and communication.
Influence of Age
Younger great egrets under three years old tend to have less vibrant breeding plumage compared to fully mature adults. The colors continue intensifying over several seasons as birds gain experience and higher social status.
The aigrettes of elderly birds eventually begin to fade again as age impairs feather structure and melanin deposition. However, well-maintained plumage can persist into the double digit years for healthy egrets.
Here is a table summarizing how breeding plumage develops across age classes:
Age Class | Breeding Plumage Characteristics |
---|---|
Juvenile | No specialized plumes developed |
1-2 years | Small plumes with pale coloration |
Prime adult | Long brightly colored plumes |
Mature adult | Maximum length and hue intensity |
Elderly | Faded, deteriorating plume quality |
Diet Influences Breeding Colors
The types of carotenoid pigments great egrets consume in their diet directly affect the colors they are able to produce in breeding plumage. Carotenoids are organic compounds found in many fish, crustaceans, and plants.
Great egrets eat predominantly fish, but also prey on amphibians, insects, crustaceans and small mammals. The balance of carotenoids obtained from these food sources influences the tint of breeding feathers each year.
Here are some key dietary factors:
Crustaceans
Shrimp and other crustaceans contain astaxanthin and other red-hued carotenoids. These pigments produce the pinkish-purple tones in plumes.
Green Plants
Lutein obtained from aquatic plants and algae generates yellows and greens in feathers. Greens can also mix with pinks.
Fish
Certain blue and green fish like trout and herring provide bright bluish pigments. Fish-rich diets favor blue hues in plumage.
Pollutants
Environmental contaminants can disrupt carotenoid deposition, leading to duller colors. Mercury and pesticides are particularly detrimental.
By selectively consuming specific carotenoid-rich foods, great egrets can optimize the brilliance and range of their breeding colors each season.
Conditions for Maximum Color
Great egrets display the most intense and elaborate breeding plumage when the following conditions are met:
– Adult age at full maturity has been reached
– Clean and abundant food sources are available
– The bird has access to diverse carotenoid pigments
– There is low environmental pollution in their habitat
– Energy can be focused on plumage rather than stressors
– Social competition for mates is high that year
– The regional climate is optimum for energetic displays
Conclusion
The flamboyant breeding plumage of great egrets serves an important seasonal purpose in courtship rituals and sexual selection. While normally pure white, great egrets develop vibrant plumes in shades of emerald, sapphire, magenta, bronze and other hues during the breeding season. The colors help attract mates, stimulate pair bonding, and signal individual fitness. Subtle variations occur based on age, diet, region and environment. When conditions are ideal, great egrets can maximize the intensity of coloration in their lacy nuptial feathers. The breeding plumes provide a temporary yet dazzling transformation of appearance.