Hummingbirds are known for their bright, iridescent plumage that shimmers in the sunlight. While most hummingbirds sport fiery reds, emerald greens and sapphire blues, the presence of true blue plumage is exceptionally rare in the hummingbird world. Only a few species of hummingbird have been documented with the capacity to display bright blue coloration. This has led many to wonder: why are blue hummingbirds so rare?
In this article, we will explore what’s special about blue plumage, examine the few blue hummingbird species that exist, and discover why blue coloration is an unusual trait in hummingbirds. Gaining insight into plumage coloration can help us better understand the diversity and evolution of these captivating creatures.
What makes blue plumage special?
In the bird world, true blue feathers are highly uncommon. This is because birds typically acquire their rainbow of colors through two types of specialized cells called pigment cells and structural cells.
Pigment cells contain melanins and carotenoids which produce darker colors like black, brown, reddish hues, and yellows. Structural color cells use refraction and interference of light to reflect blues, greens, and iridescent colors.
While many species can produce greens and violets using structural color, generating the precise structure required for bright blues is extremely challenging. Only a few bird groups like jays, rollers, and bee-eaters have mastered the anatomy to create dazzling blue hues.
Pigment production
Melanin pigments create darker black and brown tones, while carotenoids produce vibrant yellows and oranges. Both play a key role in avian coloration. However, neither can generate blue coloration.
Structural color
Structural color relies on precise nanoscale architecture in feathers to refract incoming light waves and reflect back only blue wavelengths. This requires a complex layering of keratin, air pockets and melanin granules. Even minor structural variations will result in green, violet or grey tones instead of blue.
The few blue hummingbird species
Despite the difficulties of producing blue, a handful of hummingbird species have evolved the structural colors necessary to flash vibrant blues. Here are some of the stunning blue hummingbirds that exist:
Blue-throated Hummingbird
The Blue-throated Hummingbird (Lampornis clemenciae) lives in the oak and pine forests of the mountainous regions of Mexico and the southern United States. The males are distinguished by their bright blue throats and white tipping on the tail feathers. When the sunlight hits just right, they can also display a dazzling turquoise crown.
Bahama Woodstar
Native to the Bahamas, the Bahama Woodstar (Calliphlox evelynae) is one of the smallest hummingbird species in the world. The males sport a metallic teal-blue crown and throat, with a few yellow feathers under the chin. Their name comes from the star-shaped pattern formed by iridescent streaking on their tiny tail feathers.
Blue-capped Hummingbird
In Central America, the Blue-capped Hummingbird (Amazilia cyanocephala) can be identified by its deep azure-blue crown. The males also have a white stripe behind the eye and a white tip to the tail. Their wings produce a distinctive buzzing sound in flight.
Violet-crowned Hummingbird
A native of Mexico stretching up into Arizona and Texas, the Violet-crowned Hummingbird (Amazilia violiceps) exhibits a dazzling violet-blue crown and throat in bright lighting. The females and juveniles are more subtle with green crowns and pale grey underparts.
Purple-crowned Fairy
The aptly named Purple-crowned Fairy (Heliothryx barroti) of eastern South America sports a shimmering lilac-blue crown atop its bright green body. The males also have conspicuous white tufts behind the eyes. At less than 10 cm long, it’s one of the tiniest hummingbirds around.
Rarity of blue coloration
While a few hummingbird species can generate blue hues, this plumage trait remains extremely uncommon. Here are some reasons why blue is so rarely seen among hummingbirds:
Specialized structural anatomy
As covered earlier, producing blue structural color requires precise nanostructure in the feather barbs. The air pockets and melanin layers must have exact thickness and density to refract and reflect light appropriately. These morphological requirements are difficult to evolve.
Limited diet
Carotenoid pigments obtained from food provide vibrant yellow, orange and red hues in birds. However, hummingbirds have a highly specialized nectar-based diet lacking many colorful carotenoids. This dietary limitation possibly restricts their pigment-based color palette.
Small size
Hummingbirds are the smallest birds, with tiny feathers sized in millimeters. Achieving the intricate structural morphology needed for blue in these minute feathers may be physically difficult. Larger birds likely have an easier time producing blue coloration.
No evolutionary advantage
Unlike the red, orange and green shades used in courtship displays, blue may provide little evolutionary advantage for hummingbirds. If blue color does not improve a male’s chances of attracting a mate or claiming a territory, there is no benefit driving its development.
Blue hummingbird characteristics
The few blue hummingbird species that exist share some common traits. Here are typical features of these unique blue-feathered birds:
Blue restricted to the head
Rather than covering the whole body, the blue coloration is usually limited to certain head feathers like the crown, throat and ear coverts. Concentrating the specialized feathers minimizes physiological demands.
Iridescent sheen
The blue head feathers have an iridescent, reflective quality that shifts hues based on lighting conditions. This is a key characteristic of structural color.
Small size
Most of the blue-headed species, like the Bahama Woodstar, are among the smallest hummingbird species. This allows their minute feathers to potentially produce the fine structures needed for blue.
Tropical range
The blue-headed hummingbirds all reside in tropical or subtropical climates in Central America and the Caribbean, rather than temperate regions. Some factor in this environment possibly facilitates the development of blue hues.
Males only
In all cases, the blue coloration is reserved only for the males. Females retain the emerald and white plumage shared by most hummingbird species. This fits with the theory that blue is used for sexual selection in mating displays.
Key takeaways
Here are some key summary points on blue plumage in hummingbirds:
- True blue feathers are incredibly rare in the avian world due to structural color requirements
- Only a handful of hummingbird species have evolved the ability to produce blue hues
- Traits like small size, iridescence and tropical range are typical for blue hummingbirds
- Precise nanostructure and lack of evolutionary advantage likely restrict blue coloration
- Blue feathers are limited to specific head regions and reserved for males
The gorgeous yet enigmatic blue hummingbirds demonstrate that even within the flashy, iridescent hummingbird family, the capacity to generate brilliant blue coloration remains a rare and challenging feat. Unlocking the secrets behind their unique structural plumage could help reveal key insights on evolution and adaptation in these captivating avian creatures.
Conclusion
In summary, blue plumage is rarely seen in the hummingbird family. Only a handful of species, typically limited to tropical regions like Central America and the Caribbean, have evolved the structural color necessary to produce blue hues in the male crown or throat feathers. Due to intricate structural requirements, limited dietary pigments, small size and lack of mating advantage, blue coloration appears an unusual adaptation in hummingbirds. The few blue-feathered species, like the Bahama Woodstar and Blue-capped Hummingbird, provide a unique glimpse into the spectacular capabilities of specialized avian plumage. Gaining understanding of how these hummingbirds achieve dazzling blues can provide deeper appreciation of the form and function of their stunning, iridescent feathers.
