In our previous post about bird plumage, we mentioned the colours of a bird’s feathers are mainly governed by pigments, and light. Pigmented colours are made up of three typical pigment groups.
Melanins are pigments which birds produce themselves, and as with us, it is in their skin and eyes, but also in their feathers. It is the only genetically encoded pigment; that is, it’s the only one that is predetermined in feather development.
Melanin is responsible for the blacks, browns, beiges and buff earthy colours you see in many hawks and owls, for instance. Other pigment groups that produce the yellows, oranges, pinks, reds, purples and greens are known as carotenoids and porphyrins. The structure of those pigment granules themselves determines the colours they produce, depending on which of the light wavelengths they absorb or reflect.
These birds absolutely adore dogwood berries.
These pigments are in algae and plants, and therefore the fruits, seeds and nuts of the plants, and enter the bird’s bloodstream either by direct consumption, or indirectly via another animal that has eaten them. Once absorbed into the blood they are then conveyed and deposited into the feather follicles, and the concentration of their build-up will vary greatly across species.
The final factor that gives some feathers their colours is light refraction within the structure of the feather itself. The colour blue is produced by the effect of light reflecting through air pockets inside a feather, and colours that we see along this range are called structural colours. Some birds exhibit colours that are a combination of pigmented and structural colours.
For example, in some parrots, when a layer of yellow pigment is lying on top of a particular structural set-up of a feather and then light hits that feather, the blue wavelengths are reflected back through the pigment, and the feather appears green.
A few birds can be identified just by their plumage, but out in the cold light of day, sometimes it’s not that easy. Read more!
Our cover star the northern cardinal is a very prolific bird seen throughout the United States and is so iconic that it is the state bird of Illinois, Indiana, Kentucky, North Carolina, Ohio, Virginia, and West Virginia. The all-over vibrant red of the male cardinal is down to the pigment group of carotenoids. These birds absolutely adore dogwood berries as well as wild grapes and raspberries, all rich in carotenoids. Studies were carried out to see what happened when seeds substitutedthis wild fruit in their diet, and the red plumage was decidedly less amplified, but still red – carotenoids are present in many seeds too, so they were still getting some colouration from there.
Likewise, the equally vibrant scarlet tanager is a songbird seen in the north and mid-eastern states of the US, migrating to the lower south-eastern states and South America during the winter season. Their jet-black wings strikingly off-set the otherwise all-over stunning body plumage of this aptly named bird, and if there is plentiful fruit around, their diet can be very similar to the cardinal’s.
However, their much deeper reds are provided by the array of carotenoid-richinsects they hunt for high up in the treetops. Somewhat confusingly, the Latin name for this species is Piranga olivacea, the latter part of which refers to the fact that the first specimen caught was actually a female, whose duller olive-coloured plumage is provided by a mix of more melanin to carotenoids.
However, parrots can do something other birds can’t.
Despite having at least four dominant colours to its impressive plumage, the scarlet macaw is named after the red of its head, chest and some of its tail feathers (a tail that is incidentally more than half of its body length).
These birds dine on pretty much everything from seeds, insects, fruit and nectar and flowers, but for the macaws, their favourites are beetles, larvae, and snails, beasties which are rich in carotenoids.
However, parrots can do something other birds can’t - using enzymes, they modify the carotenoids into another pigment known as psittacofulvin, which is only found in parrots, and not in other birds typical of the tropical regions. Indeed, the Latin name originally bestowed on this large parrot by Carl Linnaeus was Psittacus macao.
Into the ibis
Stalking through tropical South America and the Caribbean, scarlet ibis are identical to their cousins the white ibis in every physical way except their colouring, so much so it took a while for the science community to decide the scarlets were a separate species and not some unfortunate spray-painted white ones.
Feeding on insects like scarabs and ground beetles, they also consume shrimp, fiddler crabs, and other molluscs and crustaceans. These animals have in turn consumed plentiful amounts of algae containing carotenoids, turning them red as well. Juvenile scarlet ibis are actually born a mix of grey, brown and white, but after the second moult and once their meals start to kick in, the red creeps up over their backs then to the entire body.
This change takes around two years to culminate in the intense red of the adult plumage. Their legs and feet also turn red.
Why be such an obvious colour, in a world that is surely mostly green?
You will see that the bird is not actually all red – the tips of the wings and sometimes a large proportion of the decurved bill, especially the end, are an inky black to dark blue. This is due to the melanin present – melanin is exceptionally strong and helps to toughen up the keratin edges of the bill and flight feathers to prevent rapid damage. This is also why swan’s wing tips can appear grey-black. The scarlet ibis is the only red-coloured shorebird in the world.
Red for go
These birds and many others like them display such bright red in their plumage, oftentimes simply all over, and they don’t change their plumage across seasons. So, you do find yourself wondering: why be such an obvious colour, in a world that is surely mostly green?
Whilst you can find red birds in temperate regions of the world, there aren’t that many that are so vivid, and the brightly coloured ones like those listed above do spend a lot of time in regions that are packed with equally vibrant colours as well as green, so it will act as a form of camouflage there.
Also, when a flock of macaws takes flight in panic from a predator approaching, the resulting assault of colour makes it very hard for the predator to pinpoint just where it should attack.
The red colour is also an indicator of just how good at finding food that bird is, as with the male northern cardinals. Their breeding season is quite long (late February to August) which explains why there are so many of them, but studies have also found that the brighter they are, the more successful they are as mates: I know where the good food is at, look at me. And I have to confess, that tactic has certainly worked on me a few times.