The colour green can symbolise nature, inexperience, jealousy, and according to one holy book, immortality. But in the bird world it can help birds merge into their surroundings, or show off some amazing colours that could hide a life-saving secret.
In previous posts we’ve looked at how some birds produce the enormous range of colour in their plumage, from the striking red of the northern cardinal to the not-really-there-but-somehow-is-there blue of the common kingfisher. We know that birds get these colours in their feathers with the aid of built-in pigments called melanin and pigments absorbed through food called carotenoids with light and air providing other aspects.
Green feathers are created through a combination of two types of colouration – structural and pigmented colours.
The word green comes from the Middle English and Old English word grene, which, like the German word grün, has the same root as the words ‘grass’ and ‘grow’. Green is so abundant in nature; it stands to reason that there’ll be quite a few birds out there trying to blend in. Some birds that exhibit other colours in their plumage will often have a streak or wing bar here or there of some shade of green in order to do just that. Many females in bird species who show sexual dimorphism will be olive or pale green, keeping them and their similarly coloured juveniles safe, and then there are the other birds who are so brightly and vividly green that you wonder if they are not just an extension of the rainforests themselves.
Green feathers are mostly created through a combination of two types of colouration – structural and pigmented colours. Birds whose feathers are blue are not actually coloured blue, they just look blue to us through something called structural pigmentation, caused by air cavities in the feathers throwing back the blue wavelength of white light at our eyes. The same goes for green, to an extent. Feathers on many green birds contain these same air cavities but they are also embedded with either yellow carotenoid pigments, which produce the vivid bright greens, or yellow carotenoids combined with melanin pigments, which gives rise to the darker olive greens. The brown-headed barbet, for example, eats nothing but yellow food – mangoes, papayas, jackfruit and bananas. A combination of this yellow diet and those cavities in the feathers gives their bodies that rich and bright green.
We say mostly created because, as with a lot of things in the bird world, there are some unique little touches out there. Firstly, we look at those birds that most people associate with the word green, parrots.
You can’t parrot a parrot
The order Psittaciformes is huge and contains the 4 families of parrots: New Zealand, cockatoo, Old World and New World parrots. Coming in at around 390 species, parrots vie for being the second largest group of birds in the world, depending on whose study you’re looking at – detractors say hummingbirds have similar or maybe more species; the undisputed largest order of birds at around 425 species are the Tyrannidae, the tyrant flycatchers. An overwhelming number of parrots are very green, which perhaps presented some initial naming problems at the beginning. However, human perseverance endured and we have, among many others, the azure-rumped parrot, the chestnut-fronted macaw, the scaly-breasted lorikeet.
Coming in at around 390 species, parrots vie for being the second largest group of birds in the world.
These pretty boys and girls have exactly the same set up for feather colouring as many other birds, in that a mixture of pigments and light produces the colour green, except they had to go and be different: their greenness is unique to them in two ways. The parrot diet consists mainly of seeds, nuts, fruits, and other plant materials that all contain carotenoids, but once this is consumed, enzymes in parrot’s bodies convert those pigments into their own type of pigment, psittacofulvin, giving rise to the order name. This customised pigment is therefore responsible for all of the reds, yellows, oranges and so on that you see in parrots. If you see a blue parrot, that means they are a species that lacks psittacofulvin, and their plumage is the sole result of light scattering through their otherwise colourless feathers, give or take the presence of some black or brown melanin granules.
Birds who ingest carotenoids and then absorb those into their feathers can have their colouring affected by the volume of carotenoids they eat – the yellow chest of the blue tit gets brighter if it snacks on more caterpillars, the pink wings of the flamingo get more shocking if it gulps down more shrimp. Not so for parrots; their colour intensity remains the same, no matter how many fruits or seeds they consume containing this group of pigments. They can certainly look brighter if they eat good stuff and are healthy, but that is down to the condition of the feathers rather than a boost in pigmentation.
Heavy metal birds🤘
Another bird family who exhibits unique pigmentation actually goes one step further than parrots: instead of modifying carotenoids and using light through air cavities to make their green feathers, the turacos, a group of medium-sized brightly coloured birds who are resident to South Africa, contain the world’s only true-green pigment, turacoverdin. This pigment is chemically related to turacin, a red pigment, again, also found in turacos. So, unlike all other birds who rely on light reflecting back to make their greens, turacos are actually green through pigmentation.
These birds contain mechanisms that somehow detoxify this copper, and the brighter they are may be a ‘look at me’ signal.
Turacoverdin was originally thought to be iron-based, but is in fact copper-based. As turacos are a largely tree-dwelling species, ornithologists realised that as they all live across parts of Africa that hold the world’s richest copper belts, they must accumulate this copper through their diet of fruits, flowers, buds, and other plant matter growing there that in turn is rich in this element. Copper can be damaging to birds when accumulated at high concentrations so it is speculated and currently being studied that these birds contain mechanisms that somehow detoxify this copper, and the brighter they are may be a “look at me” signal to show how good they are at protecting themselves against something they have no choice in eating, but which would otherwise kill them.
It has also been speculated, though not definitively proven, that the denser a turaco’s forest habitat, the deeper green its plumage, while non-forest-dwelling turaco species are mostly lacking in the green pigment department.
From the not-so-drab olive green of a UK warbler in winter to the aptly named shining-green hummingbird of Colombia, the variety of green plumage on birds across the world is vast. Personally, I think that green represents luck, and that’s how I feel when I see a green bird: lucky for it and I to be alive.