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?

Like water off a duck’s back

It’s obvious where that expression, “like water off a duck’s back” came from.  Duck feathers shed water amazingly well — their plumage seems almost impenetrable.

mallard drake - feathers shedding water

Droplets of water bead up and slough (or sluff) off the outer feathers of duck plumage.  This guy had just righted himself from tipping up to scrounge algae off the rocks at the bottom of the creek bed.

No doubt part of staying warm in the chill winter temperatures and winds is staying dry, and duck plumage is intended to do just that.  Not only are the feathers incredibly dense, laid down in overlapping layers in feather tracts, but they are coated with a waxy residue from a gland at the base of the ducks tail that waterproofs them.

mallard hen

Beads of water are shed from all surfaces from head to tail end on this hen Mallard.

But what about those bare feet, exposed to near freezing water temperatures and standing on cold rocks or ice or snow for hours on end?  Feet don’t shed water, just the feathers.

mallard drake standing on ice

Cold toes?

This drake has just climbed out of the water, and is standing on ice, not something we would be comfortable doing (barefoot).  What happens when we reach for ice cubes in the freezer with wet fingers? The ice sticks to our fingers and is difficult to remove without losing some skin in the process. So how do ducks keep their wet feet from sticking to the ice?

mallard ducks-on ice

Ducks slip and slide on ice, but their feet don’t stick to the surface.

The secret is to maintain very cold toes that are the same temperature as the surface on which the duck stands or walks.  This is achieved by having arterial blood going to the foot run in parallel with the vein that is bringing cold blood back from the foot — making a heat exchange unit that promotes cooling the extremities while preserving the warmth of the body core.  Engineers have used this principle in the design of heaters and air conditioners, among many other uses.

mallard hen on ice

And this makes it nice for ducks to stand around admiring their reflections in icy pools.

Spike and the boys

“Spike and the boys” — it’s not a new band, but a herd of White-tailed deer bucks that roam the backyard and beyond.  There are three mature (big) bucks and three first-year bucks with tiny antler spikes protruding from their foreheads — hence “spikes”.  They are browsing for anything edible in the backyard on this cold, snowy day.

first year white-tailed buck (spikes)

Two of the three spikes were doing a little playful head butting in the wildflower garden.

first year white-tailed buck (spike)

Number 3 of the trio ambled over to see what all the fun was about, chewing something as he ambled.

white-tailed buck-

Meanwhile the big boys were serious about finding something nutritious to eat. They have been through this long winter drought of good forage before.

Males lose 20-30 % of their body weight during the fall rut, as they follow the does around waiting for their opportunities to mate with them.  That allows little time to eat, and consequently, they may enter the winter period of low food availability with less fat than they will eventually need to survive.  Their winter browse on evergreens, leaves, and shrubs may not sustain them completely either, and they may continue to lose weight throughout the winter, despite trying to reduce their metabolism by being less active and lowering their body temperature and heart rate: lessons that the “spikes” will need to learn quickly.

white-tailed buck-

One of the big boys has already lost a portion of his rack on the right side.  It must get tricky maneuvering those irregular curves on his head through the dense branches of the forest undergrowth.

white-tailed bucks

Spike and the boys suddenly come to full attention, looking intently at the wetland valley below the brim of the hill. There are dogs and people walking down there.

white-tailed buck running away

And off they go, bounding out of sight, raising that white tail flag to indicate to the others that it’s time to flee.

why are cardinals so red? — continued

The proximate (immediate) answer to the question of why cardinals are red is that they have a diet rich in carotenoid pigments (e.g., the pigment that makes carrots orange), and will incorporate those pigments into their feathers as they develop each year during feather molt.  To read more about this process, click here to read an article from Bird Watching Daily that explains where feather colors come from.

northern cardinal

Resident Cardinal male posing on a garden stake in the backyard.  He’s bright and he’s loud, and he makes sure his mate and all the other would-be holders of his territory know it.

But I’m interested in the evolutionary basis for why cardinals stand out among other species residing year-round in northern climates in retaining their bright red coloration instead of molting to more muted shades during the non-breeding season, like, for example American Goldfinches do.   Cardinals undergo a post-breeding feather molt, just like other species, so why risk attracting predators with bright red, when you might escape notice with a dull brown plumage instead?

summer vs winter American Goldfinch plumage

Summer (top) vs winter (bottom) American Goldfinch plumage

Does sexual selection (that is, female choice for the most beautiful male, as Richard Prum argues) play a role?  Please see the yesterday’s Back Yard Biology post for more information about the importance of beauty in female choice.)

Some additional facts regarding male-female relationships in Cardinals and their close relatives, the Pyrrhuloxias of the southwestern U.S., might help to answer the question.

Cardinal vs Pyrrhuloxia--DFW Urban Wildlife

A comparison of two closely related Cardinal species, the Pyrrhuloxia, Cardinalis sinuatus (1 and 2) and the Northern Cardinal, Cardinalis cardinalis (3 and 4). Illustration in Chris Jackson’s DFW Urban Wildlife blog.

The first thing you notice from the illustration above is that the Pyrrhuloxia male and female look more alike than Northern Cardinal male and his mate do.  Why might that difference have arisen in such closely related species? And does it have anything to do with female choice for brightly colored, beautiful males?

The second and interesting difference between the two species is that Pyrrhuloxia share a pair bond only during the breeding season, breaking up in the non-breeding season into loose, often mixed-species flocks of seed-eating birds that move around to find food in their dry, desert habitat.  Each year, males vie for available females by staking out and advertising their territories, often very aggressively.  In contrast, Northern Cardinals may maintain their pair bond year-round, often for multiple years, unless one of the pair dies, and the pair stays in the same general area in which they nested, year-round.

cardinal courtship feeding-rudiger merz

A year-round pair bond exists in Northern Cardinal mates, which renews its strength in the spring with courtship feeding.  (Photo by Rudiger Merz)

Female Cardinals are making a choice of more than just a breeding partner; they may be choosing a life partner and his residence (territory).  Richard Prum might argue: what’s a male to do, but be the most beautiful thing she has ever seen?  And if he is better looking than his neighbors, she stays with him through that year and the next.  They raise multiple broods of young Cardinals together, and he passes on his good looks to the next generations.


This is an amazing high definition video of male and female Cardinals feeding their chicks (by FrontYardVideo).

In other words, it’s possible that their long-term pair bond and high fidelity to a territory year-round makes it possible for choosy female Cardinals to drive the accentuation of  beauty (in this case, “redness”) in their male partners, to the extreme that male Cardinals never lose their red color during the year.

why are cardinals so red?

Most of the birds I see in the Minnesota backyard in the winter are variations of black and white, perhaps with a bit of chestnut, yellow-tan, or reddish accents: chickadees, nuthatches, woodpeckers, house finches, goldfinches, etc. But one bird really stands out in the winter scene, the Northern Cardinal, the male of which advertises his bright red colors all year. Forget camouflage, this bird flaunts his feathery spectacle every day; it’s the one cheery spot in the monotonous gloom of winter white, gray, and brown.

male-northern-cardinal-

Here is Mr. Studly Cardinal in the spring, with his bright red coat of feathers.

northern-cardinal

And here he is on a bright, cold, winter day, with just bare twigs between him and a potential predator.

That red advertisement in the presence of a number of predators that would love to eat him really begs the questions:  why are cardinals so red, and why are they red all year?

Let’s start with the argument recently elaborated by Yale ornithologist Richard Prum in his delightful new book:  “The Evolution of Beauty” (2017).  Prum advances the Darwinian argument for sexual selection (as opposed to natural selection), more specifically, the role of female choice in mate selection, as the basis for why some males are so ornately decorated or colorful.

peacock-and-peahen-birdeden.com

Successful male peacocks displaying to their female partners have longer, more elaborate and iridescent tails. Why?  (Photo from BirdEden.com)

The adaptationist (via natural selection) argument for why male peacocks have such long tails with intricate patterns is that this feather display proves the male is 1) stronger (able to fly away from and evade predators), 2) healthier (more energy devoted to his ornaments), and 3) more vigorous (long periods of strutting around showing off those feathers while evading predation).  Prum instead argues that it is female choice of the “most beautiful” males that has driven them to become so gaudy; that is, only the extravagantly bright and showy males will pass on their genes through successful matings.

Does this help explain why Cardinals are red?  What do you think?

I’ll add my thoughts to the discussion tomorrow.

let sleeping foxes lie

Morning coffee in hand, I ventured out to a somewhat chilly “sunroom” porch this morning and found a red fox sleeping nearby.

red fox-sleeping in snow

Morning light hasn’t made it to the backyard yet, and the thermometer on the backdoor says -10 F.

So I sat, camera in hand, and waited for the fox to wake up — for an hour and a half.  It was a long nap, perhaps needed after a long night of hunting mice, or the like.  It got boring watching the fox nap, so I opened the window for a close-up, clearer telephoto shot.

red fox-sleeping in snow

Curled up, fur fluffed up, nose tucked under tail for protection — the fox is quite comfortable at this frigid temperature.  This seems to be the typical posture of canids (dogs) sleeping in the cold.

artic fox sleeping-curious expeditions.flickr

An arctic fox sleeping in a similar position (Curious Expeditions on Flickr photostream).  Note the nice pocket of insulating snow the animal has created around it.  Arctic Fox can tolerate temperature extremes of -70 F without shivering.

wolf sleeping-Jeffrey Lepore-Science Source

A gray wolf using the same heat conservative posture while sleeping in snow (photo by Jeffrey Lepore/Science Source)

red fox-

Finally awake, now that the temperature is all the way up to O F. It must be time to get on with the day’s activities.

red fox-eating snow

First on the agenda, eat some snow — replenish some body water lost in the nightly adventure.  I could see the fox biting chunks, chewing, and licking the edges of its sleeping area.

red fox-eating snow

Licking the moisture off its muzzle

red fox-

Stretching — this is a signal that the fox will either lie down for another nap, or take off in a few minutes.

red fox-

Yawn — wow, that is a huge gape between its jaws, big enough to bite something pretty chunky. Too bad the woodchucks are hibernating.

red fox-

Looking over at me, as I tap on the window, wishing the window were open instead of closed, so I could get a better photo.

red fox-stretching

A final stretch out, and the fox is off to make its rounds of the backyard.

red fox

Happy New Year

Winter scenes from the Minnesota backyard?

frost fingers-

Snowy forest lake at sunrise?

frost fingers

Snowy forest lake after sunset?

Or something else?

frost fingers-frost feathers-frost flowers

Frost formations: some call them frost fingers, or frost feathers, or frost flowers.

What I have on my windows is an etching of frosty fingers, where the subzero cold air freezes the scant moisture on the inside of the window into amazing formations resembling all kinds of objects, or in this case an entire forest.

too cold…

It’s -13 F right now, and with a moderate wind blowing, the wind chill makes it -36 F.  That’s too cold for me, but not too cold for the hungry birds and squirrels in the backyard to come into the bird feeders for a meal.

basking gray squirrel-

Gray squirrels don’t venture out until the sun is well up on these really cold days. And before they cross snow patches to get to the feeders, they bask on the trees for a while to warm up, orienting the darker fur on their backs directly toward the sun.

basking chickadee-

Even the chickadees take a few minutes between trips to the feeder to bask a little, fluffing their feathers out to make their tiny bodies into an almost spherical shape.

basking blue jay-

The bluejay must have been too cold to move — it just sat there looking around, squinting into the sun.  I could see the wind ruffling up its feathers — brrrrrrr.

Basking to gain what little radiant heat the sun provides at this time of year can be effective in warming up, but wind currents that penetrate fur and feathers carry that precious heat away.  What can a small animal do to cope with this intense winter cold?  Activity helps, as muscles generate heat, but that comes at a cost to be repaid by eating more.  Shivering helps, and when animals are not active, muscles engage in isometric tremors that generate heat, which is also expensive, but not as much as flying or running across the snow and climbing trees.   The only animals that seem unperturbed by this weather are the feisty little red squirrels.

red squirrel-

Red Squirrels must generate a lot of heat dashing around, because they spend almost no time basking and a lot of time digging into the snow looking for buried treasures (food) and running up and down trees to stash whatever they find away.

Mug shots — take 2

Birds and mammals seem to sense when you’re staring at them, willing them to stare back so you can get a great portrait with the glowing eyes looking right out of the frame.  It’s hard to achieve though, and mammals in particular resist eye contact, as that often is interpreted as a threat to them.  This is where telephoto magnification is essential, but even when I am quite a distance away, mammals just as often turn away as I raise the lens to focus.  Obviously their eyesight is a lot better than mine.

Common Loon-

A Common Loon emerged from a dive right in front of me providing a unique close-up of the detail in its feathers.

female Pileated Woodpecker

This female Pileated Woodpecker was so busy drilling into the tree, she didn’t notice (?) me walking closer to get my best shot.

european forest buffalo (wisent)-

A European forest buffalo (wisent) intent on eating and with no interest whatsoever in raising its head to make eye contact. I can see that they have long golden eyelashes though…

javelina-

Young Javelina crossing the road in front of our car near Portal, Arizona. Hairy beasts with long snouts, beady eyes, and stubby legs, not at all related to pigs (which evolved in Eurasia), but convergent in looks and habits.

mule deer-

Mule deer look like White-tailed deer (a different species) but have enormous ears, darker (blackish) tails, and darker gray fur. Usually found only in western North America plains, deserts, mountains, grasslands, etc.  Deer don’t see as well in the daytime as some more diurnal animals, and they often stare motionless for a few moments before bounding away or turning their back on the camera.

white-tailed buck-antler growth

Antler growth begins in the spring in White-tailed bucks. This looks like the start of what will grow into a large rack, and I wonder if this guy is the same animal as the one in the next photo.  I kept waiting for this guy to turn around and face me, but no…all I got was a side view.

white-tailed buck-antlers-

I’m behind a glass door and across two backyards from big buck, but he raises his head to look toward me when I tap on the window.

mexican wolf-at the Sonora desert museum, Tucson

A Mexican Wolf just barely raised its glance toward observers as it strolled through its pen in the Sonora desert museum in Tucson.  This is a subspecies of the Gray Wolf, but is on the verge of extinction in its native habitats in the southwestern U.S. and northwestern most Mexico due to loss of open hunting areas and predator removal.  Their fur coat has accents of black and white on the back and their under hair is yellower than that of the Gray Wolf.

mountain lion-

Big cats overheat quickly in the desert sun, as this one did pacing in its pen at the Sonora desert museum. Back in its cooler cave, panting, the puma/cougar/mountain lion finally raised its head and looked in my direction. Pumas are usually found in the mountains, but will venture into grasslands and even more arid desert habitat if there is sufficient game.

Mug shots – take 1

It’s great when you can get really close to the wildlife, i.e., right in their “faces”, to grab a “mug shot”.  I didn’t get many this year, but there were a few opportunities, assisted either by my extremely long (600 mm) telephoto lens or my trusty macro, to get up close and personal with the local wildlife on our travels and in my backyard.

hoverfly-on coneflower

Hoverfly gleaning pollen and/or nectar from New England Asters.

american-painted-lady-on sedum

American-painted-lady-on fall-blooming Sedum; they came through by the dozens to congregate on late-blooming flowers

honeybees-on-new-england-aster

Honeybees foraged on New England Aster; I saw more of them this year than in the last 5 years combined.

small-carpenter-bee-ceratina-spp

A tiny carpenter bee feasting on pollen from newly opened anthers on a coneflower.

bullfrog-

We found a Bullfrog calling in a desert oasis in Arizona. Kind of ugly, but beautiful eyes…that might be a mosquito on his upper lip trying to get a meal.

chuckwalla-

A Chuckwalla was sunning itself at the Sonora desert museum in Tucson. Dark pigmented scales on its underside help it soak up heat from rocks. Chuckwallas love to hide in rock crevices and resist being pulled out from their hiding place by puffing up their body with air, expanding into any empty space in the crevice.

snapping turtle-

Snapping Turtles have large jaws and long necks, but this one was protecting itself by withdrawing into its carapace.  My what beady little eyes you have, Mr. Turtle.

Great Blue Heron-

Eye to eye with a Great Blue Heron

molting mallard ducks-

Male Mallard Duck before molting a new set of showy feathers

Black-capped Chickadee-

Chickadee with an attitude…