I’ve worked as a vitamin biologist for more years than I care to remember, examining how diet, environment and genes influence human health, including how key vitamins might have acted as a selection pressure for the evolution of human skin pigmentation (colour) types during early ancestral migrations out of Africa and across the World [1].
Given that my lifelong interest in biology was kindled by a childhood obsession for ornithology, consolidated by a subsequent passion for natural history photography, it seems reasonable to come full circle in retirement, and examine how similar genetic and dietary factors can influence bird biology, and more specifically, bird colouration, using some of my accumulated avian images to illustrate the unfolding of what is a fascinating story of discovery and understanding.
If I were forced to leave Australia tomorrow, the one thing I would miss above all else is the country’s magnificent array of glitzy and intelligent birds. No other country that I’ve visited has such an extravagantly vibrant, diverse and interesting avifauna. In this article I’m going to explore the biology of bird colour, particularly red, yellow and blue, coincidentally, our three primary colours, which are always memorably striking when part of a bird’s livery, especially when set against black.
The colour of our avifauna is a result of an interaction between two biological colour systems – one is structural, and one is biochemical based on pigments. Structural colouration stems from scattering of reflected light, while biochemical colour originates from dietary and endogenously synthesised pigments. This article examines the mesmerising beauty of bird colour. It includes a section on tips and thoughts related to photographing birds and bringing out the best artistic rendering of plumage colour.
Some simple genetics applied to the colour black
Genes are made up of DNA (a string of base pairs) and direct our cells to make proteins (for example enzymes). Birds are amniotes (egg layers) and typically have a relatively small number of genes (genome) compared to other reptilian and mammalian amniotes. The length of the genome varies from 0.91 giga base pairs (hummingbird) to 1.3 gb pairs (ostrich). Of course, genes are what determines colour variation in plumage, on bare skin, in beaks, feet and even eggs. If we look at some of the colour genes, it’s fascinating to see how predictable evolution can be. By carefully characterising bird colour phenotype (observable traits of an individual due to the interaction of genetics and environment), it is possible to see that independent changes in similar genetic machinery can lead to phenotypic similarity between hugely different species. For example, loss of the black skin pigment melanin (formed during melanogenesis) is linked to the KITLG gene in humans, but also in the totally unrelated stickleback fish [2]. Basically, evolution has made repeated use of the same genes to produce light pigmentation in animals that are as divergent as sticklebacks and humans. Of course, birds make good use of melanin for dark colouration, as does the cuttlefish, which uses melanin to produce its black ink. Like KITLG, the OCA2 gene, which is also linked to melanin, and provides colour to the skin, hair, and retina in the eyes, plays a similar role in snakes, cave fish and humans. Another key gene that many people will have heard of, and which is found in both humans and birds is the red hair gene (MC1R). MC1R regulates the type of melanin being produced, and when activated it instructs the melanocyte to switch from generating yellow or red phaeomelanin pigment to brown or black eumelanin pigment instead. Studies in birds, especially pigeons, have shown that variation in the MC1R gene controls plumage colour [3].
In fact, a recent article shows that melanin contributes to colour complexity in 9000 bird species and hence reflects what should be considered as a general conclusion for all birds [4]. As far as pigment is concerned, plumage colour stems from two classes of biochrome – dark melanins and yellow carotenoids. These two differ, since melanins can be synthesised by the birds in specialised structures called melanocytes, while carotenoids cannot, and must be consumed from dietary sources. In a sense, the carotenoids are therefore analogous to vitamins in humans. In fact, beta-carotene (β-carotene) is used by humans as a dietary precursor for vitamin A as well as being a valuable antioxidant to us (and to birds) [5]. As we’ll see, carotenoids also have bearing on bird health/individual quality.
It’s been suggested, that overall, 32% of birds have a complex plumage pattern, which in most cases relates to melanin production, rather than carotenoid intake [4]. Actually, a really good analogy has been given; carotenoids provide a broad brush to produce colour splodges, while melanin acts via a detail brush to yield more intricate designs. Having touched on melanin, the first primary colour I want to examine is red, a colour that arises through a newly discovered gene, and one that can add real spectacle to a bird’s presence.
The following slideshow depicts a few birds that are highly melanised, yet also have other subtle signals such as striking eyes or contrasting patterns
Ritzy red
Studies on red siskins and common canaries (not Aussie birds, but relevant model organisms for research) have identified a gene that allows for dietary yellow carotenoids to be converted into red ketocarotenoids via oxidation by a specific ketolase enzyme. The gene responsible encodes a cytochrome P450 enzyme (CYP2J19) [6]. This same gene (CYP2J19) has been identified as the gene responsible for red colour in the beak and legs of zebra finches [7]. The latter authors suggest that a genetic connection exists between red colour and colour vision in birds, proposing that degree of redness is an honest signal of “mate quality”. That is to say, redness advertises a mate’s ability to detoxify harmful substances (remember carotenoids are powerful antioxidants) and suggests an optimal mating outcome.
Examples of yellow carotenoids include: β-carotene, β-cryptoxanthin, Lutein, and zeaxanthin, while red ones synthesised from these via carotenoid ketolase (encoded by the CYP2JI9 gene) include canthaxanthin, 3-hydroxechinenone, α-doradexathin, and astaxanthin (antioxidant in the health supplement, red krill oil) respectively.
Ultimately, this “redness” gene is present within the genome of most of our bird species, and is certainly not limited to those which exhibit red feathers.
The slideshow below shows several birds that all use the vibrancy of red as a signal, be it on plumage or bill shield or bare skin.
While I don’t profess to know the origin and various mechanisms that leads to all the hues one finds in the bird kingdom, it is important not to jump to conclusions. The comical galahs that take over my garden from time to time are pink through to bright red, but this is not due to carotenoids in the diet. The pigment in galahs and other parrots is psittacofulvin, and is unique to parrots creating a visual array from yellow through to orange and red. Furthermore, unlike carotenoids, it is synthesised by the bird itself.
Below is a slideshow of the galahs in my garden. You can see that they have varying levels of pigmentation from pink through to a deep salmon red.
Flashy yellow
As discussed above, yellow colouration stems primarily from carotenoid pigments obtained via a bird’s diet. But it can also derive from structural colour (the way light interacts with the feather structure itself).
The slideshow below shows several birds that use yellow as a visual flag to communicate status.
One of the most interesting yellow birds in my garden is the golden whistler, a joy to observe and listen to, but a challenge to photograph. An interesting paper on this species (Relative importance of multiple plumage ornaments as status signals in golden whistlers [Pachycephala pectoralis]) [8] suggests that the whistlers striking white throat patch is the most important plumage ornament as a status signal. This means the vivid yellow and other plumage features and song are of lesser significance, but still also playing a role. However, when it comes to aggression and territory at breeding time, the white throat patch is pivotal.
The slideshow below provides multiple images of the colourful male golden whistler. While we might get excited about the yellow colour (afterall we named it “golden”), it is the white throat patch that conveys the most important message to mates and male competitors.
Beautiful blue
The colour blue is different to all other bird feather colours – There is no pigment that can turn a feather blue. What we now believe is that within the feather, melanin pigment and air cavities are located so close to one another that the distance between them is actually less than the wavelength of light. Since light scattering structures are so small, they interact with light through constructive interference. That is, the nano structural elements in blue feathers scatter light in a predictable way so that light waves are in phase and thus reinforce one another. So, there is no such things as a blue bird, even though many birds appear to be blue. The blue you see on a bird feather is very much a “structural colour.” Another way to look at this paradigm is that the 3-dimensional structure of nanochannels on feather proteins (keratins) change the perceived look of white light when it hits an apparently blue feather. The keratin structure leads to red and yellow wavelengths cancelling one another out, while in contrast, blue wavelengths of light reinforce and amplify one another. The reflected light leads us to believe the bird is actually blue. Subtle nuances in the blue colour are down to variable shapes and dimensions of air pockets and keratin structure.
My favourite use of avian blue is with the satin bower bird. They are a fascinating bird species with a striking blue-black plumage and blue eye in males. They create elaborate bowers, which they adorn with bright blue and shiny objects – often pegs or pallet wrapping straps (not so environmentally good!). Again, this is all about signalling mate quality. Indeed, when indicators of male health and condition are examined (including intensity of ectoparasites and blood parasites), bower quality and male blue ultraviolet plumage coloration were significantly correlated. So, a) bower quality predicts ectoparasite load and body size, b) ultraviolet plumage coloration predicts the intensity of infection from blood parasites, feather growth rate, and body size [9].
The slideshow below shows a multitude of blue Australian birds.
I often had a male satin bowerbird set up and maintain its bower and blue trinkets outside the window of the lecture room I used to teach in – quite the distraction! In any event, more than for any other species I can think of, blue is central to so much of this bird’s existence. However, superb fairy wrens are probably the commonest blue bird I encounter in my garden, and their remarkable blue plumage is literally electrifying as it shimmers in the sunlight and with the alacrity of their constant foraging.
Below is a slideshow showing the satin bower bird and it’s bower and collection of blue trinkets.
Brazen baldy
Birds are best known for their elaborate and attractive plumage with a graded array of every conceivable colour. However, bare skin (exposed skin, feet/legs, beaks, eye rings etc) can be quite colourful, as can fleshy growths such as combs and wattles. Quite striking colours can also be attributed to the inside of the mouth (gape) and particularly the iris of the eye [10]. This latter physiognomy is often the target for spot focus when shooting birds with a telephoto lens, so this feature tends to stand out to us photographers.
The signalling functions of bare skin are probably distinct from those of plumage: while feather signals vary due to moulting and are otherwise fixed in the long term, bare skin/parts are adaptable (colour shift is possible) in the short term. Colourful bare parts can send important signals to mates and adversaries (mate selection, competition and dominance) but are also likely to perform thermoregulatory functions.
As with plumage, bare part colouration can be attributed to pigments, structural colouration, or both. Bare skin colour is also influenced by blood flow to the skin. In terms of pigments, only melanins and carotenoids are found in bird bare skin/parts. Even in parrots that lay down unusual psittacofulvins pigments in feathers, these do not show up in bare skin/parts.
As I mentioned earlier, an important type of bare part is the avian iris. Iris colour is determined by mechanisms not present anywhere else on birds. They contain chromatophores, highly specialized pigmentation cells that contain crystalline purines (particularly guanine), pteridines, or other structural pigments. Although chromatophores are a very common structure for determining integumentary coloration in fish, amphibians, and reptiles they are found only in the irises of birds. Pigments also play an important role in eye colour; melanins, carotenoids and haemoglobin (or a combination of these) are relevant.
The slideshow below shows some very colourful and interesting eyes/irises.
I don’t pretend to know what biological elements come together to characterise the eye colour of all our beautiful bird species, but I do know the joy and awe I derive when I catch something like the striking sapphire/green eye of a great cormorant on my camera and long lens. Understanding is important, but appreciating the beauty of nature is equally important – indeed, more than ever before in todays troubled world. Humans need to revere nature, then they might be more willing to protect it.
The origins of bird colour
Recently, evidence has emerged showing that branched feathers originated in the avemetatarsalian ancestor of the pterosaurs and dinosaurs that lived during the Early Triassic Period. Tissue-specific melanosome structures in the pterosaurs suggest that manipulation of feather colour, and hence function was being used for visual communication. These creatures were the ancestors of our birds and point to the deep evolutionary origins of bird plumage colour [11]. Don’t you wish you could point your camera at one of these “Jurassic Park” creatures? Hmm, maybe not!
I created the following two images using open-source AI, so take with a very large pinch of salt:
Photographing bird colour
The goal has to be to capture the original vibrance and exquisite detail of a bird’s plumage. I don’t think there is any one single approach to achieving this, but here is a list of things (tips) that should help make your final images stick out from the crowd:
You need to fit the bird to the frame of focus; to achieve this, use good quality glass. If you’re in a zoo/aviary or other private collection, a 70-300mm or 100-400mm lens will work fine. If you’re out in the wild, I’d select a 500mm lens or longer. Either a prime or zoom will do the job. Here are some links to reviews that I wrote:
Fujifilm Equipment for Wildlife Imaging
Fujifilm XF 500mm f/5.6 LM OIS WR Lens for Nature Photography
Fujifilm XF 150-600mm f/5.6-8 R LM OIS WR Lens for Small Garden Birds
The goal is detail and colour, so try to catch birds when they are still. You can then use a low ISO and slower than normal shutter speed. While you could use a tripod, they are not particularly practical and most good telephotos now offer excellent image stabilisation. If the light is really poor, I might opt to use fill flash rather than up the ISO or use a tripod. I typically use ISO 500 in good light but drop to ISO 1250 in lower light. I don’t like to go higher than this due to noise.
I like fast lenses, that is lenses that have a large (wide) maximum aperture. This allows more light to hit the sensor. The knock-on effect is that you can use a lower ISO and/or faster shutter speed. Both of these improve image quality. A large aperture does minimise the zone of focus, but you should be okay providing you hit focus on the eye. In fact, the selective focus that a wide aperture brings is brilliant for isolating a bird from its background and allowing the bird’s plumage to standout and become the subject of the image – assuming the livery has some punch.
Most mirrorless cameras now have AI focus. I’m typically happy to use bird eye detection, but if there are a lot of branches/twigs in frame, you would be better off using “old school” spot focus. When I’m shooting birds in flight, I’d use CF (continuous focus), but for static birds (birds on a stick), I might also set SF (single focus), especially if I’m also using single spot focus.
Most cameras now yield phenomenally well-exposed images, but take care in harsh light or backlit scenes where some degree of exposure adjustment is advisable.
When it comes to shutter speed, I can achieve razor sharp bird images (static subject) handheld at 1/100 sec using a 900mm equivalent lens at ISO 500 and f/8. However, small birds move fast and to truly freeze a bird in flight you will need a shutter speed of around 1/3200 sec. You might get away with 1/2000 sec but faster is better.
It’s probably not necessary for shooting bird colour, but if you want to try and add in behavioural images as well, you should deploy “Pre-Shot” mode. This is probably the most significant development in wildlife photography in recent years. It’s a game changer because you can now catch elusive, fleeting moments that we cannot even visualise, let alone successfully actuate a shutter release at the critical moment a bird exhibits a particular behaviour; our human eye-brain-trigger finger reflex just isn’t up to the job. The fact that pre-shot can address this and permit the successful capture of visually imperceptible key behavioural moments means we can now catch images like never before.
I’ve written a full article on this topic and how to deploy it – see; Using “Pre-Shot” to Catch Wildlife Action on Fujifilm Cameras
Some general thoughts include:
- Avoid cluttered backgrounds.
- A picture only works if the eye is in focus.
- Consider graphic abstraction of colour and or patterns that are, for instance, on the wing.
- Flash will add pop to an image (okay to have the flash on the camera in bird photography).
- Learn to anticipate behaviour. For example, birds often poop before they take-off.
- Prefocus can help if you are working from a hide and you know where the bird will likely land.
- Practise, practise, practise – you are no longer constrained by film costs.
I hope you found this article interesting and enjoyed looking at the images displayed in this essay. For completion, I’ve added in some (limited) key references in case you want to learn more about the biology of colour in birds. The references in the text are hyperlinked but are also reproduced below.
References
1. Lucock MD. The evolution of human skin pigmentation: A changing medley of vitamins, genetic variability, and UV radiation during human expansion. Am J Biol Anthropol. 2023 Feb;180(2):252-271. doi: 10.1002/ajpa.24564. Epub 2022 Jun 25.
2. Boughman JW. Sticklebacks and humans walk hand in fin to lighter skin. Cell. 2007 Dec 14;131(6):1041-3. doi: 10.1016/j.cell.2007.11.029.
3. Ran JS, You XY, Jin J, Zhou YG, Wang Y, Lan D, Ren P, Liu YP. The Relationship between MC1R Mutation and Plumage Color Variation in Pigeons. Biomed Res Int. 2016;2016:3059756. doi: 10.1155/2016/3059756.
4. Galván I, García-Campa J, Negro JJ. Complex Plumage Patterns Can Be Produced Only with the Contribution of Melanins. Physiol Biochem Zool. 2017 Sep/Oct;90(5):600-604. doi: 10.1086/693962.
5. Lucock M, Jones P, Martin C, Yates Z, Veysey M, Furst J, Beckett E. Photobiology of vitamins. Nutr Rev. 2018 Jul 1;76(7):512-525. doi: 10.1093/nutrit/nuy013.
6. Lopes RJ, Johnson JD, Toomey MB, Ferreira MS, Araujo PM, Melo-Ferreira J, Andersson L, Hill GE, Corbo JC, Carneiro M. Genetic Basis for Red Coloration in Birds. Curr Biol. 2016 Jun 6;26(11):1427-34. doi: 10.1016/j.cub.2016.03.076. Epub 2016 May 19.
7. Mundy NI, Stapley J, Bennison C, Tucker R, Twyman H, Kim KW, Burke T, Birkhead TR, Andersson S, Slate J. Red Carotenoid Coloration in the Zebra Finch Is Controlled by a Cytochrome P450 Gene Cluster. Curr Biol. 2016 Jun 6;26(11):1435-40. doi: 10.1016/j.cub.2016.04.047. Epub 2016 May 19.
8. van Dongen, Wouter & Mulder, Raoul. (2007). Relative importance of multiple plumage ornaments as status signals in golden whistlers (Pachycephala pectoralis). Behavioral Ecology and Sociobiology. 62. 77-86. 10.1007/s00265-007-0440-0.
9. Stéphanie M. Doucet, Robert Montgomerie, Multiple sexual ornaments in satin bowerbirds: ultraviolet plumage and bowers signal different aspects of male quality, Behavioral Ecology, Volume 14, Issue 4, July 2003, Pages 503–509, https://doi.org/10.1093/beheco/arg035
10. Rosalyn Price-Waldman, Mary Caswell Stoddard, Avian Coloration Genetics: Recent Advances and Emerging Questions, Journal of Heredity, Volume 112, Issue 5, July 2021, Pages 395–416, https://doi.org/10.1093/jhered/esab015
11. Cincotta, A., Nicolaï, M., Campos, H.B.N. et al. Pterosaur melanosomes support signalling functions for early feathers. Nature 604, 684–688 (2022). https://doi.org/10.1038/s41586-022-04622-3
All images and text are copyright Mark Lucock, reproduction without prior permission is not allowed