Wonders of Peru: Iridescent Hummingbirds
Birds produce color through various mechanisms, including pigment-based coloration, light scattering from nanostructured feather tissues, and combinations of both. Among birds, hummingbirds are particularly renowned for their brilliant, iridescent colors. The source of this vibrant coloration is nit simply due to pigments, but rather to a complex interplay between light and the nanostructured feathers of the bird.
Feather Structure and Pigmentation in Hummingbirds
Hummingbirds exhibit a distinct form of iridescence, which is achieved through the interaction of light with specialized structures in their feathers. These birds possess pigment organelles—tiny structures located at the outermost layer of their feathers—that contribute to the creation of shiny, reflective iridescent colors.
In hummingbirds, the pigment organelles, also known as barbules, are uniquely flattened compared to those in other birds, where they are typically round. Inside these flattened barbules are layers of melanosomes, small, air-filled discs arranged in stacks. The number of melanosome layers can vary, with some barbules containing up to 15 layers.
Light Interaction and Color Formation
When light hits the edge of a barbule, it first passes through a thin layer of transparent keratin and encounters the top layer of melanosomes. Some of the light is reflected, while the rest continues through the layers, refracting (bending) as it goes. This process continues as the light passes through successive layers of melanosomes, with the light being bent at different angles each time. When the light waves from these multiple reflections align, they reinforce each other, resulting in the vivid, iridescent colors observed in hummingbird feathers.
This intricate layering and the refractive properties of the melanosomes are key to the creation of the spectacular, shifting colors seen in hummingbirds and some other bird species with iridescent feathers.
The Sparkling Violetear and the Blue-mantled Thornbill - Two Distinct Displays of Iridescence
Pictured here is the Sparkling Violetear, a hummingbird that regularly displays its iridescent feathers, shining brightly throughout the day as it flits around the garden. The bird’s striking iridescence makes it a standout, with its vivid hues visible even in moderate light.
However, not all hummingbirds are as bold in displaying their colors. Many species are more discreet and shy, especially those that inhabit higher altitudes. A good example is the Blue-mantled Thornbill, a species that lives in the wild at mountainous regions. If you are fortunate enough to spot a male Blue-mantled Thornbill, the first thing you'll likely notice are his brownish upperparts and perhaps a steel blue stripe along the sides of his wings. The bird’s colorful gorget—a patch of iridescent feathers on the throat—remains hidden unless you are lucky enough to have the bird face you directly with sunlight striking his chest. When this happens, the sun’s rays reveal a dazzling display as the color transitions from emerald green through pink to purple-violet, creating a vibrant burst of iridescent hues that remains largely elusive to the casual observer.
Sources:
