Happy Christmas Eve! The weather has been frigid lately due to the extreme winter storm sweeping across the U.S., as you may have heard, so I haven't gone outside much. However, I've been doing a lot of reading and birding from inside my house. Today's Biocap discusses sparrows and colors.
As part of my wintertime routine, I have been spreading white millet across a patch of mulch close to my feeders. This is to attract ground-feeding birds, and how well it has worked! This week, there has been a constant frenzy of juncos, sparrows, doves, and cardinals to where I put the millet. Every time I look outside the window, I see at least ten or fifteen dark-eyed juncos just hopping around in the mulch and leaf litter. Dark-eyed juncos are small, sparrow-like birds that have snow-white bellies, pink beaks, and white outer tail feathers that flash when they take flight. Their plumage varies greatly. In fact, the Dark-eyed junco is split into 14 subspecies (and has a nightmare reputation among systematists, the people that research its taxonomy)!
The variation that I see is the slate-colored variation, which is the most common one. Slate-colored juncos have a, well, slaty coloring throughout most of their body except their belly, which is white. Females appear browner than males. Dark-eyed juncos are nicknamed "snowbirds" due to their arrival in abundance during the winter (in the U.S.), and their disappearance in the summer, heading for their breeding grounds in Canada.
Alongside the juncos, I spotted White-throated sparrows. These sparrows are identifiable by their namesake white throat, crown stripes that can be tan or white, and yellow lores (lores are spots above the beak). Like the juncos, they spend their winters in the U.S. and migrate north up to Canada in the summertime. It was great that I got to see these birds in my backyard, as they have been severely declining over the past several years in my area. Every winter, it had seemed there were fewer and fewer white-throated sparrows, and it was almost a relief when I saw four or five of them mixed into the junco flocks this winter. Here's a video taken from my spotting scope--- sorry for the bad video quality, its shot through my phone into the lense of the scope.
Both of these winter migrants exhibited their classic "scratch and hop" technique when foraging for the millet. Every time they hop, they kick back their feet, digging into the earth and uncovering the soil to find seeds underneath, something unique to sparrows and their allies. Outside of the sparrows and juncos, I saw mourning doves and cardinals eating the millet as well. Mourning doves used their beaks to dig around for the seeds, while cardinals kind of pecked at the ground. It was marvelous to see all the different foraging techniques being presented, and not just in ground feeders. I've seen chickadees and titmice use their "grab and go" strategy, where they flit to the feeder, take a seed, and flit back to a nearby branch or shrub to process their food. Starlings like to stab their long, thin bills at everything--- into the tube feeder, in the lawn, and through the pile of seed on the tray feeder. Blue jays and red-bellied woodpeckers both like to cache their food in little cavities in trees or the ground (both are aggressive species, could this be a coincidence?). I think this is one of the best parts about birds: their diversity in foraging strategies, and the charm in each one.
Speaking of all these birds, do you ever wonder what forms the colors on them? The bright red of the cardinal, the iridescence on the neck of the mourning dove, even the white and gray of the junco?
Recently, I've been looking into what creates colors in birds, and what I've read is rather interesting. I've learned that there are two ways to make color in feathers: pigmentary and structural. Pigments are basically colored substances that only reflect certain wavelengths (thereby emitting only a specific color) through atomic-level processes. Structural colors are created using a matrix of proteins in the feather that bends light. That protein is mostly keratin, plus some embedded air or melanin. Structural coloration takes advantage of a phenomenon called constructive interference, where two waves of light of equal frequency rise and fall at the same time. This intensifies their amplitudes and thus their color. The proteins are arranged in such a way that light coming into contact with it scatters in phase (rising and falling at the same time) and structurally creates colors through interference. Most blues in birds are created through this process (such as in the bluebirds below).
While I haven't quite gotten into the complex world of structural colors, I've gotten to know the basics of pigments quite well. The most common pigments found in birds are melanin and carotenoids. Melanins are the most abundant, being deposited in organelles called melanosomes that are found within skin cells and feathers. There are two classes of melanins: eumelanins and phaeomelanins. Eumelanins produce blacks and grays, and pheaomelanins produce more earthy tones. Since they are made within cells, their placement is highly controllable. Some of the most intricate patterns found in birds are made from melanins, like in the ornate feathers of the Great Argus (search it up!). Melanins also have the added benefit of making feathers stronger and flight more efficient. This is why many birds who depend heavily on flying, such as seabirds, have black wings or black wingtips.
Carotenoids, made from carbon chains, acquired in a bird through their diet because they are only produced in flants, algae, and fungi. They re-emit warmer colors: reds, oranges, and yellows. Carotenoids are the reason a cardinal is red, or a flamingo is pink. Only a few dozen of the hundreds of cartenoids that exist in nature are found in birds. Some carotenoids can even alter the regular appearance of birds when presented, such as rhodoxanthin, a vibrant red carotenoid found in invasive honeysuckle. When these honeysuckle appeared in the ranges of native birds such as waxwings, flickers, and orioles, the rhodoxanthin in the berries "dyed" the birds. The normal orange breast of the oriole became red. The yellow tips of cedar waxwing tails became orange. The bright yellow shafts of Northern flickers became pink. Just goes to show how big of a role pigments can play in a birds' appearence.
Melanins and carotenoids aren't the only pigments birds use. For example, porphyrins, a nitrogen-containing molecule similar to hemoglobin. They are produced by altering amino acids. They produce very interesting and exotic shades of red, browns, greens, or pinks. They often interact with melanins to produce the browns of owls. Porphyrins shine through most in a family of birds called turacos (pictures below), displayed in their spectacular purples and greens. In fact, one of the porphyrin pigments is called turacoverdin, which produces the vivid green in many turaco species. It is one of the few green colors in birds produced by pigments. There are also psittacofulvoids, fundamentally different from carotenoids and only found in parrots.
Well, that's it for my Christmas Eve Biocap. May you all have a Merry Christmas and happy holidays, and may you see a bright red cardinal in the snow! Signing off, Amber.
Sources on color:
Thompson, Mya. “How Birds Make Colorful Feathers | Bird Academy • the Cornell Lab.” Academy.allaboutbirds.org, 11 Aug. 2015, academy.allaboutbirds.org/how-birds-make-colorful-feathers/#:~:text=Pigment%20colorization%20in%20birds%20comes. Accessed 25 Dec. 2022.
Lovette, Irby J, and John W Fitzpatrick. Handbook of Bird Biology. Wiley, 2016.
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