Hummingbirds owe their beautiful iridescent plumage to ‘pancake-like’ cells in their feathers
Hummingbirds owe their famous iridescent plumage to “pancake-like” cells in their feathers, according to new research.
An international team of scientists conducted the largest optical study of its kind to find out why the native birds shine so brightly.
Hummingbirds display intense irisity – they seem to gradually change color when viewed from different angles, such as light from a bubble.
No other bird seems to have the iridescent color of a hummingbird, but scientists were not sure why.
After studying 35 different species of hummingbirds under microscopes, they discovered that this was due to the shape and arrangement of melanosomes – small structures in cells that synthesize light-absorbing pigment.
The pancake-like flatness of these melanosomes influences the way in which the light reflects them and gives a greater range of colors.
A close-up of a ruby-throat hummingbird feather with a red iridescence that is very directional and appears as a dull black from various angles
“We call these iridescent colors ‘structural colors’ because they depend on structural dimensions,” said co-author Professor Matthew Shawkey, a biologist at the University of Ghent, Belgium.
The international team examined the feathers of 35 species of hummingbirds with transmission electron microscopes.
They then compared them to those of other brightly colored birds, such as green ducks, to look for differences in their makeup.
All bird feathers are made from keratin, the same material as human hair and nails, and are structured like small trees, with parts that look like a trunk, branches and leaves.
The ‘leaves’, called feather barbules, consist of cells that contain pigment-producing organelles, or cells, called melanosomes, that produce the dark melanin pigment that colors human hair and skin.
The shape and arrangement of melanosomes can influence the way in which the light reflects and produce bright colors.
“A good analogy would be like a bubble. If you only look at a little soap, it will become colorless, “said Professor Shawkey.
“But if you structure it correctly, if you spread it very thinly to form the scale of a bubble, you will get those shimmering rainbow colors along the edges.
Costa’s hummingbird with beautiful iridescent purple throat feathers that catch the light
‘It works in the same way with melanosomes. With the right structure you can change something colorless into something very colorful. “
While ducks have log-shaped melanosomes with no air in them, hummingbirds’ melanosomes have the shape of a pancake and contain many small air bubbles.
The flattened shape and air bubbles of hummingbird melanosomes provide a more complex set of surfaces.
When light shimmers from those surfaces, it bounces away in a way that produces irisity – the effect of luminous colors that appear to change when viewed from different angles.
“In mammals, the melanin is not organized in a beautiful way in the hair, but in birds you get these layers of melanosomes, and when light returns from the different layers, we see bright colors,” Dr. said. Chad Eliason at the Field Museum in Chicago and the lead author of the study.
Wide-billed hummingbird with clear turquoise or metallic green feathers on their upper parts and chest
The study also discovered that the different properties that make hummingbird feathers special – such as the melanosome shape and the thickness of the feather lining – are properties that have evolved separately.
There are more than 350 species of hummingbirds that live exclusively in the western hemisphere, from Alaska to the tip of South America.
“Not all hummingbird colors are shiny and structural – some species have a dull plumage and in many species the females are less colorful than the males,” said co-author Rafael Maia, a biologist and data scientist at Instacart.
The study, published in Evolution, opens the door to a better understanding of why hummingbirds develop the specific colors that they do.