Bird species on Earth,plumage colouration courtesy of carotenoid pigments
Illinois,August8: There are about 18,000 bird species on Earth, and every species is differently coloured.
While some birds are so bright in colour, one can spot them from afar, some are coloured so as to camouflage- you’ll never realise if you’re even looking at the bird! The feathers are composed of intricate combinations of mottles, scales, bars, and spots, making each one unique.
Dr. Ismael Galvan and his team of expert researchers conducted a study on about 9000 bird species’ plumage coloration to answer the very question. Two types of pigments are responsible for the plumage coloration: melanins, which produce a range of black, grey, brown, and orange colors, and carotenoids, which are used by specialized feather structures to generate brighter color hues.
Carotenoids, present in certain food items, circulate through the bloodstream and to the feather follicles when birds consume such food items. The birds cannot produce carotenoids, nor can they exercise direct cellular control of synthesizing and depositing carotenoids. The specialized feather structures react to the consumed carotenoids with a mechanism that is not regulated by specialized cells.
Melanins, on the other hand, are synthesized by in the birds’ bodies in special cells called “melanocytes,” which work together with feather follicles to achieve a fine control of pigmentation. Although carotenoids are more frequently reseached in the study of bird coloration, Dr. Galvan and group are the first to test whether melanins are indeed the only pigmentary element that birds’ bodies directly control on a cellular level.
Galvan says, “Knowing beforehand that different pigments and structures produce different types of colors in feathers, we examined the appearance of the plumage of all species of extant birds and determined if the color patches that they contain are produced by melanins or by other pigmentary elements. We also identified those plumage patterns that can be considered complex, defining them as those formed by combinations of two or more discernible colors that occur more than two times uninterruptedly through the plumage.”
According to the researchers, 32% of the species studied have complex plumage patterns, with the vast majority of these complex patterns produced by melanins rather than carotenoids. In other words, carotenoids produce color patches, whereas melanins produce intricate patterns
However, there are exceptions: have . Fruit doves, cotingas and one type of stork have complex plumage patterns without melanins. Their unusual colors appear to be produced by their bodies making metabolic modifications to the carotenoid pigments that they consume.