How do birds make colourful feathers?
The incredible variety of colours and patterns exhibited by Southern African bird life is certainly a feast for the eyes and a handy visual aid for us to identify individual species. Most importantly, the colours and patterns of birds are a key indicator of specific survival strategies. They give us a glimpse into the fascinating world of bird behaviour.
At a basic level, survival means finding enough food while avoiding predation. But it’s also about finding a mate and mating successfully to ensure the passing on of an individual’s genes. Since birds can see in colour, colours and patterns are an important tool for recognising one’s own species and attracting potential mates.
Colour, mating and survival
Within the Aves class, there are two main survival strategies related to colouration – bright colours, and dull colours that aid with camouflage. Both strategies have pros and cons.
Brightly coloured birds such as Greater Double Collared Sunbirds and Woodland Kingfishers are immediately attractive to potential mates because of their vibrant colours. The downside is that their bright colouration often makes them stand out from their surroundings and be more visible to predators. On the other hand, birds such as Doves and Crested Francolins prefer hues that blend with their surroundings utilising camouflage to remain undetected by predators. These less colourful birds must rely more on courtship rituals and song to find a suitable mate and maintain pair bonding.
How birds’ colourful feathers are formed
Now we know why birds colouration is so important to their survival, let’s have a look at how birds’ colours are actually formed. It turns out that it’s more complex and interesting than just “bright” and “dull” birds.
The colours in bird feathers are formed in two ways. Generally, the colours are formed by pigments or by the refraction of light caused by the structure of the feathers themselves. In some cases, the colours are the result of a combination of pigments and structural colours.
Colours formed by pigments
The majority of bird species owe their beautiful colours to the pigments in their feathers, the two most important pigments being melanin and carotenoids.
Melanin
Melanin is produced by the body and depending on its concentration and location, produces colours like black, reddish brown, or pale yellow. Melanin also serves to strengthen feathers and make them more resistant to wear and tear. You’ll notice that there are many mostly white birds that have black feathers on their wings or wing tips. The melanin not only provides a black appearance but also adds strength to the primary and secondary feathers that are subjected to the most wear and tear.
Carotenoids
Carotenoids are naturally occurring pigments synthesised by plants and are responsible for the yellow, orange and red colours of many plants. They are also responsible for the bright yellows, reds, oranges and other hues of bird feathers.
Carotenoids are absorbed through the diet of birds, either by eating plants or by eating something that eats plants (like insects). Once ingested, the carotenoids travel through the bloodstream to the dermal follicles from which feathers develop; these follicles supply blood and colour to the growing feathers.
This also means that the intensity of a bird’s colouration can be an important indicator of its health. It indicates whether the bird is getting enough food and whether its body is working optimally to convert the carotenoids into the pigments in its plumage.
Structural colours
Adding to the diversity of avian colours are colours produced by the microstructure of the feather. Instead of pigments, these colours are produced as light is refracted by the proteins within the microscopic structure of the feather. There are two ways that the structure of a birds feather creates colours, tyndal scattering and iridescence.
Tyndal scattering
A special kind of diffraction of light, called the Tyndall effect, can produce the blue colour of many birds, including some species of Kingfishers and Rollers. In these species, small, finely dispersed reflecting particles (often pockets of air) in the feathers, reflect blue and violet colours.
Blue colours in feathers are almost always caused by tiny air pockets in the barbs of the feathers themselves that scatter incoming light, particularly the shorter wave lengths of light (like blue), resulting in the spectacular blues. Blue is refracted and the remaining colours are absorbed by a layer of melanin.
