There are thousands of species of birds here on Earth and with those great numbers come
great biodiversity.
Birds are among the most colorful animals on the planet, and scientifically speaking,
it’s because different species can employ a wide range of chemical and physical tricks
to make them stand out – or disappear – depending on what suits them.
When looking at the plumage of a bird, there are really two factors that define the “color”
that you see – pigmentation and structure.
Pigments are chemicals that absorb certain wavelengths of visible light, leaving the
remaining light to be reflected from a surface to give it its color, while structural colors
are produced by the way that the physical structure of the feather interacts with visible
light.
Birds are also “tetrachromatic,” which means they can see four colors: all the colors
we see, plus they can also reach into the UV spectrum too!
This has lead to certain species of birds to develop plumages that are more complex
than we can even perceive!
There is a variety of forms of pigmentation in birds, but we are going to focus on three
different kinds, carotenoids, melanins, and porphyrins.
Some of these pigments are produced in bird’s bodies, while others are taken from food sources.
Different species of birds use different combinations of them to create unique looking plumages.
Carotenoids are a diet-based class of pigments that birds ingest from food and deposit into
their feathers.
These yellow to red pigments give foods like carrots and corn their color.
Carotenoids are broken into two subgroups, oxygen-containing xanthophylls and oxygen-less
carotenes.
Flamingos for example, are gray when young, but after eating enough carotenoid-containing
brine shrimp and algae, they become pink.
Other birds metabolize the ingested carotenoids to create their color, which is how yellow
canaries get their yellow and cardinals get their red.
Melanin is a pigment found in many animal species, including ourselves!
Unlike carotenoids, these pigments are produced in the feather by special cells called melanocytes,
and there are two different types.
Eumelanin create blacks and grays, while pheomelanin is often buff, brown, or chestnut in tone.
What makes melanin stand out from other pigments is that it also acts to reinforce the structure
of the feather, strengthening the wings for flight.
This is why the tips of feathers and the feathers on wings are darker.
One of the less common forms of bird pigmentation comes from compounds called porphyrins.
Generally, these web-like molecules are responsible for vibrant colors in biology - hemoglobin
and chlorophyll are good examples.
In birds, these usually produce different shades of brown, as in the feathers of owls
and bustards, but also can create vibrant reds and greens, as in birds like turacos.
But what really makes porphyrins stand out to birds, is that they fluoresce in a bright
red under UV light!
Beyond pigments, so-called structural coloration also can generate a diverse array of feather
colors.
These are produced in feather barbs and barbules by microstructures that can absorb or scatter
different wavelengths of light to produce a range of colors and visually striking effects.
First and most basic, white comes from the un-pigmented keratin layer on the exterior
of a barb.
The intensity and brightness of the white is dependent on how light is bounced around
by tiny air vacuoles inside.
To create structural colors like blue, in an area just below the keratin exterior, keratin
rods and air vacuoles of various shapes and sizes assemble together and scatters or absorbs
certain colors of light, bouncing off another to produce what you see.
It’s then backed by a black layer of melanin to make sure the effect isn’t wrecked from
light coming in the other direction.
This type of structural color can create ultraviolet patterns too.
Angle-dependent effects of these colors are also possible, which is the case for iridescence.
The physical cause is similar to how structural blue is made.
The way light bends off of the structures changes our perception of color based off
of the angle of viewing and the incidence of light.
Also, nano-structures in some bird feathers can take almost all light away too, producing
a black that’s blacker than black!
Researchers discovered recently that structures in birds of paradise are so effective at repeatedly
bouncing light, that they absorb 99.95% of the light that hits them!
These many different methods of producing color can combine to create the amazingly
colorful spread of bird feathers.
We never asked, how many birdwatchers do we have out there?
Bird science is a recent discovery for us, and we want some more topics to cover – post
them down in the comments below!
Thanks for watching.