Category Archives: Bird Anatomy

Where The Color Comes From

Indigo bunting (photo by Marcy Cunkelman, May 2015)
Indigo bunting (photo by Marcy Cunkelman, May 2015)

Why does the indigo bunting (Passerina cyanea) look so blue?  It isn’t from the color of his feathers.  In dull light he looks gray!

Last month when I wrote about blue morpho butterflies I learned that their color comes not from pigments but from the structures of their scales that reflect blue light.

This same color trick is what makes indigo buntings’ feathers so blue.

Watch the Deep Look video below to learn how it works.

 

(photo of indigo bunting by Marcy Cunkelman, video from Deep Look on YouTube)

The Dance Makes A Difference

How can we tell when similar birds are actually different species?

In the jungles of Indonesia the male superb bird of paradise (Lophorina superba) is famous for his courtship dance.  To attract a mate he calls loudly, unfurls his jet black feathers and iridescent green apron, and starts to dance.  If he’s really good at it, the female accepts him.

The bird’s color and dance are so mesmerizing that ornithologists at first dismissed the differences between the eastern and western birds. Now they’ve looked more closely.

This video from Cornell Lab of Ornithology shows how the western bird’s behavior convinced scientists to split the superb bird-of-paradise (Lophorina superba) into two species.

The dance makes a difference.  The bird with the sidestep gait is now called the Vogelkop superb bird-of-paradise (Lophorina niedda).

 

p.s. Volgelkop is the name of a peninsula in western New Guinea, Indonesia where this bird lives.  On the map the peninsula is shaped like a bird’s head.  Vogel+kop means “Bird head” in Dutch.

(video from Cornell Lab of Ornithology)

Why Ducks Are Hard to Identify in Flight

American wigeon pair on the water (photo from Wikimedia Commons)
American wigeon pair on the water (photo from Wikimedia Commons)

It’s relatively easy to identify ducks on water because they look like the pictures in the field guides.

Even when the female is boring, the male is usually colorful as shown in this pair of American wigeons (Mareca americana).  He’s the one with a green nape, white crown, white butt, and black tail.  The black and white features are unique, even from a distance.

But in flight it’s another story.  Here are three American wigeons in the air.  I’m stumped!

American wigeons in flight (photo from Wikimedia Commons)
American wigeons in flight (photo from Wikimedia Commons)

Why are they so hard to identify? Because we see two body parts that aren’t visible when they’re swimming — bellies and underwings.  Who knew that wigeons have white bellies?

The best way to identify ducks in flight is by using black-and-white drawings.  This Washington Department of Fish and Wildlife brochure is the closest thing I’ve found online:  Ducks at a Distance.  See pages 50-51.

 

(photos from Wikimedia Commons; click on the images to see the originals)

What The Pigeon Sees

Field of View diagram: pigeon and owl (illustration from Wikimedia Commons)
Field of View diagram: pigeon and owl (illustration from Wikimedia Commons)

How does a pigeon avoid being lunch for a peregrine falcon?

He flies fast, he stays in a flock for protection, and he (quite literally!) keeps an eye out for danger.

Pigeons have such a wide field of view that they can see danger coming from almost any direction.  There’s only a narrow place in front of them where both eyes focus and a narrow blind spot in the back.   Pigeons are not alone. Many prey species have a wide field of view.

This is hard for us to imagine because our eyesight is like the raptor’s but raptors seem to know how it works.  When a peregrine wants to sneak up on a pigeon he flies in the pigeon’s blind spot.

Read more about what the pigeon sees in this vintage article:  Anatomy: Field of View

 

(illustration from Wikimedia Commons; click on the image to see the original)

Is This Bird Right Handed?

Eurasian kestrel holding a dragonfly (photo by Dr. Raju Kasambe via Wikimedia Commons)
Eurasian kestrel holding a dragonfly (photo by Dr. Raju Kasambe via Wikimedia Commons)

We humans have a trait called handedness in which we show a preference for using one hand over the other.  The vast majority of us are right-handed.

Do birds have handedness, too?

Indeed, they do.  Birds show it by the foot they use, the eye they look out of, and the crossing of their bills.

Feet? Eyes? Crossed Bills?  Read how birds express handedness in this vintage article Anatomy: Right Handed?

So what do you think?  Is this Eurasian kestrel right-handed?

 

(photo from Wikimedia Commons; click on the image to see the original)

Yellow Is A Sign of Spring

White-throated sparrow (photo from Wikimedia Commons, Creative Commons license)
White-throated sparrow (photo from Wikimedia Commons, Creative Commons license)

Even before the buds burst and the flowers bloom, birds give us a hint that spring is coming.  Some of them turn yellow.

* White-throated sparrows have boring faces in the winter but their lores turn bright yellow ahead of the breeding season. They’ll leave in March or early April for their breeding grounds in the northern U.S. and Canada.

* American goldfinches were brownish all winter but molt into yellow feathers in late winter. Even the females turn a subdued yellow as seen in the female on the left in Marcy’s photo.

Goldfinches turning yellow for spring (photo by Marcy Cunkelman)
Goldfinches turning yellow for spring (photo by Marcy Cunkelman)

* At this time of year European starlings become glossy and their beaks turn yellow.  The starling below is male because the base of his beak is blue (near his face).

European Starling in breeding plumage (photo by Chuck Tague)
European Starling in breeding plumage (photo by Chuck Tague)

 

There are other birds whose yellow facial skin becomes brighter in the spring.  Can you think of who that might be?  …

Yellow is a sign of spring.

 

(photos from Wikimedia Commons, Marcy Cunkelman and Chuck Tague. See credits in the captions)

Who Is This White Hawk?

Leucistic red-tailed hawk near Berthoud, Colorado, 2017 (photo by Pat Gaines via Flickr)
Leucistic red-tailed hawk near Berthoud, Colorado, 2017 (photo by Pat Gaines via Flickr)

Have you ever seen a distant white raptor and hoped it was a snowy owl or gyrfalcon?  I have, but I’m usually wrong.  Both species are rare and neither is here in spring or summer.

Snowy owls and gyrfalcons only visit Pennsylvania in late fall or winter.  In most years snowies don’t come to the Pittsburgh area at all (this year is an exception) and gyrfalcons are never here.  In over 100 years only 41 gyrfalcons were reported statewide (see *1 below).

And yet we still see an occasional rare white raptor, even in the summer.  What hawk is this?  In nearly every case it’s a leucistic red-tailed hawk.

“Leucism is a condition in which there is partial loss of pigmentation in an animal resulting in white, pale, or patchy coloration of the skin, hair, feathers, scales or cuticle, but not the eyes.” (quoted from Wikipedia).  The condition is rare but red-tails are our most common hawk so it’s not surprising to find it in a numerous population.

The whiteness varies from hawk to hawk and even from year to year.  Sometimes leucistic red-tails are spotted brown, sometimes they’re entirely white.  Pat Gaines photographed a speckled one in Berthoud, Colorado this winter (above) and an all-white bird in North Denver in 2010 (below).  Neither bird is albino because its eyes are the normal color, not pink.

Leucistic red-tailed hawk in North Denver, Colorado, 2010 (photo by Pat Gaines via Flickr)
Leucistic red-tailed hawk in North Denver, Colorado, 2010 (photo by Pat Gaines via Flickr)

Even the all-white birds have at least one normally-colored feather.  It’s a tail feather on this hawk, as shown in Pat’s photo below.

One red tail feather: Leucistic red-tailed hawk in North Denver, Colorado, 2010 (photo by Pat Gaines via Flickr)
One red tail feather: Leucistic red-tailed hawk in North Denver, Colorado, 2010 (photo by Pat Gaines via Flickr)

So what makes them white?

A study of color aberrations among Indian birds listed six reasons for pale or white feathers. (Download the report here: How common is albinism really? Colour aberrations in Indian birds reviewed.)

  • Albino (pink eyes) is a hereditary pigment error. Albinos are rarely seen because they die young due to poor eyesight.
  • Leucism (normal eyes) is a hereditary lack of both melanin pigments.  Some feathers are normal color.
  • Progressive graying.  Oh my!  A few birds turn “gray” as they age, becoming progressively whiter as they molt each year.
  • Brown. Normally black feathers are brown and sensitive to light so they bleach out in the sun.  This mutation is only expressed in females.
  • Dilution. Black feathers are silvery gray.  Therefore the bird looks pale.
  • Ino is like albino but not as severe. The bird does not have pink eyes and thus lives longer than a true albino.

Even so, we can’t know why each bird is white without a lot of study.

So who is that white hawk in Pennsylvania?  It’s probably a leucistic red-tailed hawk.

 

(photos by Pat Gaines)

(*1) How rare are gyrfalcons in PA?   In 1982 and 1984, DVOC’s Cassinia analyzed all the reports of gyrfalcons in Pennsylvania. From the mid 1870’s to 1984 only 41 were confirmed: Gyrfalcon Records in Pennsylvania, Part One, 1982 and Gyrfalcon Records in Pennsylvania, Part Two, 1984.  Most reports were in Schuykill, Carbon, Berks, Lehigh and Lancaster counties with only 2 reports at Presque Isle, Erie County (there have been more since then).  As of 1984, the most recent sighting of a gyrfalcon in Pittsburgh’s 11-county metro area was 1 bird in Westmoreland County in January 1913.

The Back Toes

Snow Bunting in winter plumage (photo from Wikimedia Commons)
Snow Bunting in winter plumage (photo from Wikimedia Commons)

Birds’ feet vary a lot from species to species.  Hawks have talons, ducks have webbed feet, and marsh walkers have very long toes (like this jacana).

Even their rear toes differ based on their life styles.

On Throw Back Thursday, learn about the back toes at:  Anatomy: Musing on Rear Toes.

 

(photo from Wikimedia Commons; click on the image to see the original)

The Letters W And Z

Evening Grosbeak specimen at the Smithsonian, male, female and gynandromorph (photo by ap2il via Flickr, Creative Commons license)
Evening Grosbeak specimen at the Smithsonian, male, female and gynandromorph (photo by ap2il via Flickr, Creative Commons license)

What makes birds two-sided like this, both male and female in the same body?

 

Bilateral gynandromorph northern cardinal (photo courtesy Western Illinois University)
Bilateral gynandromorph northern cardinal (photo courtesy Western Illinois University)

It’s a very rare condition and it only happens when there’s an embryo error in the bird’s sex chromosomes, W and Z.  The resulting oddity is a “bilateral gynandromorph.”

Learn how it occurs in this last-day-of-the-year article … Anatomy: W and Z

 

(photo credits: evening grosbeaks at the Smithsonian by ap2il via Flickr, Creative Commons license. Northern cardinal courtesy of Western Illinois University. Click on the images to see the originals.)

The Best Snood Wins

Wild turkeys displaying (photo by Cris Hamilton)
Wild turkeys displaying (photo by Cris Hamilton)

Here’s some trivia for Turkey Day.

Did you know you can determine a male turkey’s health and his success with the ladies by the length of his snood?

What’s a snood?

On humans it’s a large-mesh hairnet worn by women, or …

Women workers wearing snoods, 1942 (photo from Wikimedia Commons)
Women workers wearing snoods, 1942 (photo from Wikimedia Commons)

… a beard snood worn by men.

Beard snood sold by Creeds, UK (image from Creeds UK)
Beard snood sold by Creeds, UK (image from Creeds UK)

But on turkeys the snood is the piece of flesh that dangles from the male turkey’s forehead and droops over his beak.

Here’s a Wikipedia diagram of the male turkey’s anatomical ornaments:
1. Caruncles, 2. Snood, 3. Wattle (Dewlap), 4. Major caruncle, 5. Beard

Diagram of a turkey's head and chest ornaments (image from Wikimedia Commons)
Diagram of a turkey’s head and chest ornaments (image from Wikimedia Commons)

The two wild turkeys at top are displaying to females.  Which one has the best snood?  I can’t tell but the females can.  Click here to see how the ladies reacted.

 

(photo credits:  two wild turkeys by Cris Hamilton; women wearing snoods from Wikimedia Commons; man wearing a beard snood from sales page at Creeds UK; wild turkey diagram from Wikimedia Commons. click on the images to see the originals)