The complex plumage colouration of birds is mainly produced by melanins, which create a range of black, grey, brown, and orange colours, scientists say.
Researchers at University of Chicago in the US explored the role of melanins in creating complex plumage patterns in 9,000 bird species.
Birds' feathers, or plumage, are some of the most strikingly variable animal characteristics that can be observed by the naked eye.
The patterns that we see in birds' feathers are made up of intricate combinations of mottles, scales, bars and spots.
"For many birds, plumage colouration may make them less visible to predators by helping them to blend in to their surroundings, or more appealing to potential mates by helping them to stand out from their peers," said Ismael Galvan from University of Chicago.
Researchers studied plumage colouration to see what types of pigments were present in birds' complex feather patterns.
Plumage colouration mainly happens due to two types of pigments: melanins, which produce a range of black, grey, brown, and orange colours, and carotenoids, which are used by specialised feather structures to generate brighter colour hues.
Birds cannot produce carotenoids on their own. They must consume food items that contain these pigments and the carotenoids circulate through the bloodstream and to the feather follicles.
Melanins, on the other hand, are synthesised in the birds' bodies in special cells called "melanocytes," which work together with feather follicles to achieve a fine control of pigmentation.
Although studies frequently focus on carotenoids in bird colouration, 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.
"We examined the appearance of the plumage of all species of extant birds and determined if the colour patches that they contain are produced by melanins or by other pigmentary elements," Galvan said.
"We also identified those plumage patterns that can be considered complex, defining them as those formed by combinations of two or more discernible colours that occur more than two times uninterruptedly through the plumage," he said.
The study examined about 9,000 bird species, with the goal of supporting a general conclusion for all birds, to finally answer the question of how birds develop colourful and detailed patterns.
The team found that about 32 per cent of the species studied have complex plumage patterns, with the vast majority of these complex patterns produced by melanins rather than carotenoids.
A few birds are exceptions to this rule: Three bird families do have complex plumage patterns without melanins.
Fruit doves, cotingas and one type of stork have unusual colours that appear to be produced by their bodies making metabolic modifications to the carotenoid pigments that they consume.
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