the benefits of black feathers

Adding to the white, gray, and brown monotone colors of the winter landscape now, the resident birds also seem to be mostly shades of black, white, and gray or tan.  In fact, many of them use black as a primary “color” of their plumage.  Is black somehow advantageous to birds in the winter?

american crow-

Of course, crows are black all year, so their plumage color can’t be an advantage just for winter time.

I usually feel warmer with a dark colored sweater or jacket on a cold day, and we know that black absorbs and holds radiant heat energy much better than other colors.  So, do birds utilize their dark brown/black feathers to stay warm?

turkey vulture basking

Turkey Vulture basking in early morning on a northern California riverside.

Some birds, like Turkey Vultures, Anhingas, Cormorants, and Roadrunners, do use their dark plumage to advantage to warm up on cold mornings, basking with their dark feathers spread widely apart so heat can reach the skin below.

anhinga basking

Anhingas dry their feathers by spreading their wings, but their dark brown back feathers also give them a boost of warmth on cool mornings.  Photo taken on the Anhinga Trail in the Everglades.

However, wind ruffling the feathers of a crow reveals a flaw in the idea that their black feathers are used to keep them warm.  Their feathers are only black right at their tips, and are white-gray underneath; in fact their skin is pale as well.

american crow-white feathers beneath black ones

A crow sitting high on a tree branch in a steadily blowing wind must feel the chill on a day when the temperature is below 0 F.

This seems more like an adaptation to avoid overheating in summer sun, than conserving heat in winter cold.  In summer heat, black feather surfaces would heat rapidly, becoming warmer than the surrounding air, and would enable the bird to actually unload heat produced internally, reflected through the whitish underlayer of feathers to their outer surface.  This helps explain how large-bodied, dark-feathered Ravens can survive in hot, arid environments as well.

raven-grand canyon

Soaring above the canyon keeps them cool, but down at the bottom of the canyon where the food might be found often gets well above 100 F.

Assistance in regulation of body temperature might be one explanation for why so many birds have black feathers or black-tipped feathers, but there are a host of other possible explanations, as well.  One likely possibility is that the melanin pigment that colors the feather dark brown to black (depending on its concentration) binds to the keratin protein in the feathers and strengthens them and helps them resist wear.

birds with black wingtips

Large-bodied, white birds with black wingtips.  White Ibis photo by Ronnie Maum; Snow Goose photo from Birds of North America online; Northern Harrier photo by Jerry Ligouri.

During feather development, granules of melanin are deposited in the helical strands of keratin protein that make up the filaments that are in turn packaged into the barbs and barbules that make up the feather.  Melanin-enriched keratin has been demonstrated to make feathers stiffer, more durable, and resistant to abrasion.  The outer (primary) flight feathers are the propellers in the generation of powered flight, making it essential for them to be stiffer and wear-resistant.

But what are the benefits of black plumage patterns in all the other birds we see in the winter landscape?  Is black important for thermoregulation, resistance to wear, cryptic camouflage, something else…?

black and white birds

Birds in the Minnesota backyard, clockwise from upper left: Downy Woodpecker, Black-capped Chickadee, Yellow-bellied Sapsucker, White-breasted Nuthatch, and Northern Flicker.

Your thoughts?  What about all those other mostly black birds:  Red-winged Blackbirds, Pileated Woodpeckers, Puffins, Anis, Petrels, Auks, Grackles and Cowbirds, Coots, Moorhens, Frigatebirds, Starlings, and more.  Why black?

The Color of Birds: pigments

There have been a couple of questions recently about how color is controlled in bird feathers, so I thought I would explain that with some examples from some of my bird photos.  One excellent explanation of coloration in bird feathers can be found at the Cornell Lab of Ornithology’s website:  http://www.birds.cornell.edu/allaboutbirds/studying/feathers/color/document_view

To summarize their information, the color of bird feathers is formed in three ways:  by pigmentation of the feather, by structural properties of the feather, or a combination of both.  This post is about just the pigment part of color production.

There are three basic contributors to feather pigmentation:  melanin, carotenoids, and porphyrins.

Melanin pigments give feathers a yellow-brown to black appearance, the density of color depending on the amount of melanin present.  The presence of the melanin or any pigment actually strengthens the feather, and so we often see birds with white wings and black wing tips (e.g., gulls, terns, and white pelicans).  However, melanin also makes the feather more susceptible to bacterial degradation, leading to frayed wing tips which are not good for the long distance flyers or aerial maneuvers.

White Pelican from Lac Qui Parle dam, Minnesota.

Carotenoids may be derived from plant compounds like the xanthophylls we see in yellow, orange, or red leaves in the fall or carotene we see in carrots.  They must be eaten by the birds as the feathers are growing in during a molt, and some are modified by the bird to produce a specific color.  Examples are the yellow of Goldfinches or the yellow and orange colors in some tropical tanagers and spring warblers.

Flame-colored Tanager in Boquete, Panama

Porphyrins are metalo-proteins synthesized from amino acids, like the heme protein in the hemoglobin of our red blood cells.  These pigments produce pink to red colors, and in combination with melanin pigments produce the rich reds, brown, and greens of some tropical bird species, as well as owls, pheasants, turkeys, and other fowl.

Male Quetzal in Bouquete, Panama.

QUIZ TIME:

What pigments produced the color in this Keel-billed Toucan?