Hello again, folks! Last week, I covered the four basic ways by which birds can be colored. This week, we're going to zoom in on a few groups of birds that have entirely unique forms of coloration.

We'll start off with a stunning bird family that many of you may not be familiar with: The turacos. These guys produce copper-based red and green pigments, turacin and turacoverdin, respectively. Having copper in their pigments already makes turacos distinctive, but they also stand out in the fact that they are the only birds to use a green pigment – most bird species get green coloring from the combination of yellow pigments and blue structural coloration.

Here we have a gorgeous Red-crested Turaco to show off turacin in its crest and turacoverdin in most of its body feathers. Perhaps turacos are not the most well-known family of birds, but they are certainly worth learning about, with their extraordinary coloration.

The striking yellow highlights on many penguin species comes from spheniscins, a group of pigments produced only by penguins. It has been known for a long time that penguins have a unique pigment, since they are able to maintain the coloration without eating carotenoids. Only in recent years have scientists begun to figure out the molecular structure of spheniscins, though more research is needed to clarify it.

You can see the use of a spheniscin in this Yellow-eyed Penguin's lovely spectacles. Fun fact: spheniscins fluoresce under UV light. We can only imagine what it's like for penguins to look at each other, since we humans lack the capability to detect UV light.

Many parrots have red, yellow, and/or green coloring. This is due to yet another unique class of pigments, the psittacofulvins, produced only by members of the order Psittaciformes. Psittacofulvins have both red and yellow varieties, as seen in the Rainbow Lorikeet in the cover photos.

Here we have a Monk Parakeet modeling the green coloration for us. The green effect is seen as the result of blue structural coloration combining with the yellow psittacofulvin.

The male Lawes' Parotia (aka Six-wired Bird-of-Paradise) has an iridescent breast patch that relies on more than just the usual refractive thin film mechanisms for iridescence. The barbules of the feathers in that patch are modified in a way that essentially makes them act as three different colored mirrors, allowing for dramatic color changes as the bird shifts position.

This wonderful 1873 artwork by Daniel Giraud Elliot is the only image I could directly put in the article, but here's a link to a set of photos and a video of their courtship display. Magnificent birds!

This concludes my two-part series on bird coloration. Hopefully you've enjoyed getting a little peek at the complexity of avian design; I know I've certainly had a blast writing about it!

Sources: Flickr creative commons for all images except the psittacines, which I took myself; "Dramatic colour changes in a bird of paradise caused by uniquely structured breast feather barbules" by Doekele G. Stavenga, Hein L. Leertouwer, N. Justin Marshall, and Daniel Osorio; National Geographic Bird Coloration by Geoffrey Hill; "Vibrational spectroscopic analyses of unique yellow feather pigments (spheniscins) in penguins" by Daniel B. Thomas, Cushla M. McGoverin, Kevin J. McGraw, Helen F. James, and Odile Madden.