Boldly Invisible

A continuation of the discussion in the last post of why black accent or coloration is so widespread, especially in small birds…there are still more questions to answer.

For example, you would think that a boldly striped, black and white animal would be an easy target to spot against the homogeneous green or gold African savanna.

zebra-

But how many zebra do you actually see here?

Disruptive patterns of black and white break up the outline of an animal’s body, making it difficult to detect them in a complex background.  Maybe this is why a herd of zebra can be referred to as a “dazzle”?

Looking at a single chickadee against a plain white or tan or gray background makes them standout because of their bold black and white markings.

Black-capped chickadee-

But finding them in their more typical, complex background of myriad tree branchlets and leaves is much more difficult.

chickadee family-no highlights-

How many chickadees hiding in the bushes?  They blend in well with highlights of snow on branches or in the background, deep shade on unlit branches, and the tan of leaves and bark.

chickadee family-with highlights-

Here they are!  Highlighted with a little illumination in Lightroom photo editor.

Birds that live in complex environments like the dappled shade of a forest, or the complex vegetation of a wetland or grassland, often have complex feather patterns (especially dark and light) that more or less blend with their background, or at the least, make them difficult to detect until they move.  Some of the boldest black and white patterns, like the stripes on a Kildeer’s breast, actually distract one’s eye from the outline of the bird’s body.

kildeer-defending-chicks-

Until she moves, mama Kildeer isn’t obvious in this marshy wetland. I didn’t even notice her chick standing silently on her right until I was editing the photo for a blog post.

Some birds emphasize camouflage even more by combining spots of white or bands of dark and light on their feathers.

barred-owl-camouflage

A sleeping Barred Owl has pretty good camouflage in this leafless Amur Maple forest.

barred-owl-close-up

Stripes down its breast and spots on the wings and back of the Barred Owl help break up the solid outline of its body.

brown creeper-

The blotchy brown and white plumage of Brown Creepers lets them hide in plain sight on the rough bark of mature trees where they forage in crevices for prey.

So, one of the answers to why so many birds, especially those residents that live in the northern temperate forests all year, adopt splotchy patterns of black or brown and white plumage is that they maximize their ability to hide in plain sight by being boldly invisible.

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?

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.

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

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 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…

winter blah — happy solstice everyone

The lyrics from California dreamin’ are running through my head this morning as I look out at our ever-present gray world:  “all the leaves are brown (the ones still on the tree), and the sky is gray (for days on end)…”

deer-herd-in-the-snow-

It’s a gray world…

And the weak sun screened behind the dense clouds doesn’t help much.  This is the time of the winter solstice, the least daylight we’ll have this year.  According to the experts that track these statistics, those of us at 45 degrees north latitude will have 8 hours and 46 minutes of dim light today, and the sun will rise only 21.5 degrees above the horizon at noon.

For comparison, that’s 6 hours, 51 minutes less light today than during the June solstice, when the sun rose to 68.5 degrees above the horizon at noon.  Here’s what that difference in sun angle looks like in geometric space.

eorbit3 from zebu.uoregon.edu

Path of the sun and its position at noon for viewers at 45 degrees north latitude, at winter solstice (21.5 degrees) and at summer solstice (actually 68.5 degrees, not 66).  For those interested in how to calculate the angle of the sun at solstice, click here for a description from an earlier post.  Diagram from zebu.uoregon.edu

It’s no wonder that animals and humans alike just want to curl up and rest until the sun comes back out again.

sparring in the snow

The deer herd wandered through the backyard for the first time in quite a while.  A few does, three bucks, and assorted youngsters of the year.  Two of the bucks got into a couple of short shoving matches, primarily instigated by “big buck” (he of enormous girth photographed in mid-November).   The rut might be mostly concluded, but there seems to be enough residual hormone circulating to ensure the male dominance hierarchy is still on-going in the herd.

White-tailed deer bucks

“Big buck” on the approach to his younger, smaller herd member…

White-tailed deer bucks

One minute they are ambling through the woods picking up the stray leaves and twigs to eat…and the next minute they are butting heads.  Buck on the left is getting shoved backward by “big buck”.

White-tailed deer bucks

Ouch, “big buck’s” antler tine looks like it’s poking into the smaller buck’s right eye.

White-tailed deer bucks

Staring contest — who’s the boss? You can tell “big buck” is asserting his dominance just by the difference in the posture of the two.

One minute they are ambling through the woods picking up the stray leaves and twigs to eat...and the next minute they are butting heads. 

Back to amicable feeding, side by side…

One minute they are ambling through the woods picking up the stray leaves and twigs to eat...and the next minute they are butting heads. 

and then suddenly, “big buck” turns to face off with his buddy again…(the difference in the size of the two bucks is more noticeable in this shot, and their antlers seem to be different colors)

White-tailed deer bucks

once again locking horns (antlers)…

White-tailed deer bucks

and once again, the smaller of the two bucks gets a tine in the eye

Now we see the advantage of that larger, more complex rack on older bucks, with tines that can reach into the sensitive facial areas of their competitors.  Of course, the added stature and muscle mass helps those big bucks push their smaller competition around as well.  Thanks for the show, boys.

running on water

Watching ducks and swans take off from the mostly unfrozen lakes the other day, I was impressed with how important those big, webbed feet are in keeping the birds’ bodies up near the surface of the water.  For example, a light-bodied, male Hooded Merganser “ran” on the water less than 50 feet before it was air-borne.

male hooded merganser running on water

The merganser’s feet barely touched the water surface as its rapid wingbeats lifted it into the air.

These small diving ducks weigh only 1-2 lb, so getting air-borne from the water surface is less of an impressive achievement.  However, Trumpeter Swans, the heaviest bird in North America, weigh 20-30 lb, and lifting those big bodies into the air requires the combined effort of both feet and wings.

trumpeter swans running on water

Initially, it looks like a lot of splashing without much lift taking place.

trumpeter swan running on water

Their bodies are so close to the water on take-off, they can’t utilize their powerful wing down-stroke for lift, so the large surface area of the feet really is essential in pushing the bird up.

trumpeter swan running on water

Even as the bird begins to lift above the water surface, it still can’t use the down-stroke for lift;  the feet continue to propel the bird upward.

And those are some really big feet aiding the launching effort.  Swans rarely show off those big appendages that are so useful in water take-offs, as well as digging up the bottom sediment while they forage.

trumpeter swan landing-

Coming in for landing with webbed feet fully extended to brace for impact…

The birds with probably the longest required take-off pathway from water are the loons.  With relatively short wings and legs placed far to the rear, loons need two to three times the distance for take-off that ducks do, and as they take-off, they too appear to be skipping along the water surface — or even hydroplaning.

loon running on water-northof49photography.com

A Common Loon (or Northern Diver) in mid-take-off (photo by northof49photography.com)

The true masters of “running on water”, however, have to be the Western Grebes, whose courtship dance is a synchronized ballet of movement across the water, all performed without a single wingbeat, paddling with just their feet in completely upright posture.  A clip from David Attenborough’s Life of Birds shows this incredible feat the best.