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?

Of fantastic horns and survival strategies

In an earlier post, I noted that antelope horns can be used for dissipating heat or male-male combat or in some cases for defense against predators.  But the variety of horn shapes and sizes in African antelope is truly impressive, as we found when driving around the Safari West wildlife reserve a few days ago.  Perhaps they have some undiscovered uses as well.

Addax, or Screwhorn Antelope are native to the Sahara desert, but critically endangered in the wild because of overhunting.  Both males and females sport long twisted horns that typically grow to about 3 feet in length.

Addax, or Screwhorn Antelope, are native to the Sahara desert, but critically endangered in the wild because of overhunting. Both males and females sport long twisted horns that typically grow to about 3 feet in length. Their pale reflective hair coat and nocturnal habits enable them to survive in the arid desert where they eat primarily succulent plants.

A look-alike to the Addax is the Scimitar-horned Oryx (or Sahara Oryx) that is now extinct in the wild.  They exist only in zoos and wildlife reserves (like Safari West).

A look-alike to the Addax is the Scimitar-horned Oryx (or Sahara Oryx) that is now extinct in the wild in its native Sahara desert habitat. They exist only in zoos and wildlife reserves (like Safari West), but in the wild their survival strategy was similar to that of the Addax:  forage at night on succulent fruits and plants, seek shade in the daytime.

At least this oryx has found an additional use for his long curved horns as a back-scratcher.

This Oryx has found an additional use for his long curved horns as a back-scratcher.

The Gemsbok, one of four species of Oryx and native to South Africa, has incredible heat-tolerance and water conservation strategies that enable it to survive in harsh desert habitats.

The Gemsbok, one of four species of Oryx and native to South Africa, like other Oryx species has incredible heat-tolerance and water conservation strategies that enable it to survive in harsh desert habitats.  Allowing its body temperature to rise during the daytime to 113F (45C) and drop again at night to 95F (35C) reduces its need to sweat or pant to cool off. But brain temperature remains constant by diverting hot blood from the body to its cool nasal passageways.  Do its elongate horns help eliminate heat? Unknown.

The Waterbuck, despite its name, does not live in or near water.  But those long horns must be good for something since this antelope wanders around in sub-Saharan scrub and savanah where long horns would seem to be at risk of getting entangled in vegetation.  Are they for thermoregulation?

The Waterbuck, despite its name, does not live in or near water. But those long horns must be good for something since this antelope wanders around in sub-Saharan scrub and savanah where long horns would seem to be at risk of getting entangled in vegetation. Are they for thermoregulation?

This bull Eland doesn't need long horns for protection; it's the largest antelope and its imposing stature would probably intimidate most predators.

This bull Eland doesn’t need long horns for protection.  It is the largest antelope species in Africa and its imposing stature and musculature would probably intimidate most predators.

Broken horns are not likely to regenerate, as the growth tip is damaged and blood supply interrupted.  Does this make the individual with one horn less likely to survive in it native habitat?

Not a unicorn, but close.

Not a unicorn, but close.

Horns vs Antlers

We took the California grandkids on safari (at a wildlife/conservation preserve near Santa Rosa, CA) to meet some of Africa’s lesser known antelope and bird species.

On safari at Safari West, Santa Rosa, CA

On safari at Safari West, Santa Rosa, CA.  Granddaughter got tired and is sleeping on her dad in the shaded seat.

Sometimes the wildlife gets really close.  Note grandson's expression.

Sometimes the wildlife got really close. Note grandson’s expression.

But this wasn’t just about seeing wildlife, we learned a lot too.  For example, our guide explained the differences between horns and antlers with a demonstration.

Horns are hollow sheaths of bone covered with a thin layer of epidermal tissue, the outer sheath of which is a keratin covering like a fingernail.

Horns are hollow extensions of skull bone covered with a thin layer of epidermal tissue, the outer sheath of which is a keratin covering like a fingernail.  This is the skull of the an Ankole-Watusi cow, seen below.

Horns are permanent structures, they keep growing as the animal ages, and are primarily for defense (or offense in the case of combative males) and thermoregulation (getting rid of heat).  In addition, usually both sexes of members of the Bovidae (cattle, antelope, and goats) have horns.

Ankole-Watusi cattle at rest in the middle of the day under a leafless tree.  Because of the lack of shade, the cattle flush blood through their horns to dissipate heat.

Ankole-Watusi cattle at rest in the middle of the day under a leafless oak tree. Because of the relative lack of shade, the cattle flush blood through their horns to dissipate heat.

Ankole-Watusi cattle are native to Africa, and quite distinctive for their elongated horns that can reach up to 8 feet wide.  The interior of the horns are honeycombed with a lattice of bone that carries blood vessels to the exterior keratinized sheath which then radiates the excess heat to the environment.  So, this bone is living tissue.

This herd adopted a stray wild boar piglet that wandered into the 100 acre antelope enclosure at Safari West.  He nursed from the cows (who rejected any other calf than their own) until maturity and now rests in their shade.

This herd adopted a stray wild boar piglet that wandered into the 100 acre antelope enclosure at Safari West. He nursed from the cows (who rejected any other calf than their own) until maturity, and now seems to be a member of the herd, resting (at lower left) when they do.  

Antlers, in contrast, are almost always present only in the male of members of the Cervidae family (deer, moose, elk, and other small Asian deer species), with the exception of the caribou (or reindeer) in which females have smaller antlers than the males.  In addition, they are grown anew from buds on the skull each spring and summer and shed each winter after the rut season. They are useful as indicators of male vigor — i.e., for fighting and as sexual attractants to females, but not for thermoregulation because once the velvety covering is shed before the rut, the bone dies and lacks further vascularization.

A handsome buck I found in my backyard in November 2012.

A handsome buck ready for battle I found in my backyard in November 2012.  See post on “My trophy buck.

The largest set of antlers (by weight and tip to tip length) belonged to the extinct Irish Elk (Megalocerus giganteus — that species name says it all) that stood almost 7 feet at the shoulder and sported a 12 foot wide rack weighing about 90 pounds.  What an investment to make for just getting a female’s attention!

Face-off

You rarely see two male dragonflies get this close without doing battle.

The male 12-spotted skimmer on the right attempted to usurp this perch from the male on the left, but was chased away.

The male 12-spotted Skimmer on the right attempted to usurp this perch from the male on the left, but was chased away.

There is a reason the male on the left wants that particular position — it’s somewhat shaded, and it’s a hot day with the sun directly overhead and high humidity.

Notice how the dragonfly has flexed his abdomen downward and perches behind the stake to shade himself somewhat.

Notice how the dragonfly has flexed his abdomen downward and is perched behind the stake to shade himself somewhat.

When he is perched this way, it gives me a much better look at his whole face. Now all we need is some names for those parts.

12-spotted skimmer face

Here’s a diagram I made in Photoshop that I hope accurately labels the parts.

12-spotted skimmer head-labeled

Starting at the top, you can see the short antennae emerging just above the darkened area of the vertex (triangle between the eyes), in which the primary light sensing ocelli are placed. Ocelli (there are three of them) are simple eyes (i.e., not compound) are used to detect changes in light intensity and duration, not for visual acuity.

The front of the dragonfly’s “face” is composed of the dark, bumpy frons and the much paler, two-segmented clypeus, which lie above the upper lip or labrum (looks like a mustache on this dragonfly).  This part of the face is the only part we usually see in horizontally perching dragonflies.

The real chewing apparatus of a dragonfly is composed of the mandibles and the maxillae (probably named for their similar roles in mammals) which lie directly below the labrum.  They are attached at the side of the head, coming together in the middle for tearing/crushing action, and when fully opened provide a wide gape entrance to the mouth.   No wonder they can chew up their prey so quickly and effectively.

Thanks to a hot, hot day and a 1917 textbook on dragonfly anatomy, I now know a little more about dragonfly faces.