We introduce White River jeweler and artist Roy Sarkin, a keen and knowledgeable birdwatcher. He’s kindly agreed to share his regular birding blogs with us.
Feather Colour in Birds
Feather colouration in birds is conferred either by pigments or by structural phenomena intrinsic to the keratin (of which a feather is made) itself. The most abundant pigment in feathers is melanin; eumelanin is black or dark brown, phaeomelanin is paler or rusty red. Another common avian pigment is a group called carotenoids which are bright red, orange or yellow.
The only other feather pigments in birds are those unique to the Afrotropical loeries (now called Turacos). The beautiful red we see when a loerie flies is called turacin and the green one is called turacoverdin, which is the only green pigment found in any bird in the world!
All other green feathers show the combined effect of a structural blue associated with a yellow carotenoid, or simply the effect of iridescence. Iridescence and scattering are two visual effects dependent on the microscopic structure of the feathers keratin. Iridescence as seen in starlings and sunbirds with green, blue or violet reflections, depends on the layering of highly crystaline, clear sheets of keratin overlying each other and reflecting light of relatively short wavelengths.
Below these outer layers of the feather is a dense layer of eumelanin granules, black in colour, which absorb all other wavelengths of light passing into the feather, thereby enhancing the iridescence colour. Longer wavelengths give a more golden iridescence. All these iridescence effects can be seen in the eye of a peacock’s feather.
Scattering depends not on layering but on a finely irregular structure of the keratin, between which are air spaces. If all the wavelengths of light are scattered, a feather looks white, unless there is some melanin in it to give a greyish effect. If only the short wavelengths of light are scattered the feathers look blue: this in known as Tyndall scattering and is common in kingfishers, rollers and many green birds other than turacos. As with iridescence, the intensity of the blue is enhanced by absorbing the transmitted wavelengths of light in a deep layer of melanin granules. The outer layer of the barb of such a feather consists of clear keratin, the cortex. Below the cortex is the medulla in which the scattering is done by threadlike ramifications of keratin enclosing air spaces. In the core of the barbule of the feather is the layer of melanin granules.
Talking about turacos, the next time you see one have a look at its feet. They are zygodactyl (two toes forward two toes back) – zygodactyl means yoke toed. I will talk more on bird feet next time as it’s a subject on its own.
As can be seen from the above there is more than meets the eye when you look at a bird and see its beautiful feathers. We were at Olifants Nature Reserve at the beginning of April and there were still some European Bee Eaters around. The only other migrants we saw were female and juvenile Red Backed shrikes and juvenile Wood Sandpipers (the juveniles often overwinter). The juveniles have a brown wash on their necks and their back feathers are scalloped with an off-white colour compared to the adults white. We also saw more than ten Lesser Grey shrikes which is the most we have ever seen on one trip. We saw Tawny eagle and Bateleur eagles displaying and two African Hawk eagles attacking another eagle in the sky and chasing it away. We also saw two Spur Winged geese in the river.
Roy can be found in his shop at Casterbridge Lifestyle Centre, Roy Sarkin Jewellers, phone 013 751 2747. Birding is his hobby and he’s delighted to talk avian with any passersby!