Category Archives: Bird Anatomy

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 specimens at the Smithsonian. Male, female and gynandromorph (photo by ap2il on Flickr)

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 captions 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)

For Best Results Copy Birds

Thirty years ago Japanese trains had a problem. They could travel fast but they caused sonic booms.

The answer was the bullet train.  How did Japanese engineers develop it?  They learned from birds.

Watch this 6+ minute video from Vox + 99% Invisible to learn how birds showed the way and follow one woman’s quest to teach engineers that Nature has the answers.  Our world can benefit from biomimicry.

For best results, copy birds.

 

Thank you to Holly Hickling for sharing this.  For more cool videos, follow Vox (news site) or 99% Invisible (city design updates) on Facebook.

(video from Vox on YouTube)

The Wax Eaters Are Back In Town

Yellow-rumped warbler in autumn (photo by Cris Hamilton)
Yellow-rumped warbler in autumn (photo by Cris Hamilton)

After most warblers have left for the winter, the yellow-rumped warblers come back to town.

Breeding across Canada and the northern U.S., yellow-rumped warblers (Setophaga coronata) spend the winter in North America as close to us as Ohio and eastern Pennsylvania, though not usually in our area.  In late fall they stop by in Pittsburgh.

Yellow-rumps don’t have to leave for Central or South America because they have a unique talent. Their bodies can digest wax.  In winter they eat the waxy fruits of bayberry and juniper.  Since bayberry is also called wax myrtle, it gave our common subspecies its name:  the myrtle warbler.

On Throw Back Thursday, learn how yellow-rumped warblers get nutrition from wax in this vintage article:  Anatomy: Wax Eaters.

 

p.s. Notice that the warbler in the Wax Eaters article is wearing bright breeding plumage in black, white and yellow . Autumn yellow-rumps are dull brown with a faint vest and a broken white eye ring. The best clue to their identity is their yellow rump.

Yellow-rumped warbler showing its yellow rump (photo by Cris Hamilton)
Yellow-rumped warbler showing its yellow rump (photo by Cris Hamilton)

(photos by Cris Hamilton)

When Birds Lost Their Teeth

 Model of Archaeopteryx on display at Geneva natural history museum (image via Wikimedia Commons)
Model of Archaeopteryx on display at Geneva natural history museum (image via Wikimedia Commons**)

Birds have no teeth but that wasn’t always the case. We know that they’re descended from toothy theropod dinosaurs — in fact birds are dinosaurs — so when did they lose their teeth?

In 2014, genome sequencing studies led by Robert W. Meredith worked to determine whether several branches of birds’ ancestry lost their teeth independently (convergent evolution) or whether all birds have a common ancestor that evolved a toothless beak.

The project did full genome sequencing on 48 birds species representing nearly all modern bird orders.  They then focused their study on six genes related to tooth enamel.  All six genes became non-functional in a common bird ancestor around 116 million years ago.  That’s when birds lost their teeth.

Birds eat plenty of things that require chewing so how do they do it?  Read this 2010 blog post Anatomy: Where Are Their Teeth? to find out.

 

More information on the bird genome project is here in Science magazine.

(cropped image of Archaeopteryx model on display at Geneva natural history museum via Wikimedia Commons; click on the image to see the original.  **Note that this Archaeopteryx model has accurate teeth but has other inaccurate/disputed features as described on Wikimedia Commons: “Archaeopteryx had a more round shape of its wings, the primary feathers were attached to the second finger unlike here, and these colours are now known to be wrong.”)

How Old Is That Peregrine?

Adult peregrine falcon in flight, Univ.of Pittsburgh, 2016 (photo by Peter Bell)
Adult peregrine falcon in flight, Univ.of Pittsburgh, 2016 (photo by Peter Bell)

Now’s a good time to brush up on identifying peregrine falcons since they pass by hawk watches in October, especially on the coast.  When you identify a peregrine you can also tell how old it is because the plumage is different in each age group:  adult, juvenile, and sub-adult.

Plumage provides an exact age for two groups in October:  Juveniles are first year birds, 6 months old, that hatched last spring. Sub-adults are second year birds, 18 months old, with nearly complete adult plumage.

Adults — two or more years old — all have the same plumage.  Unfortunately you can’t know an adult’s exact age unless the bird is banded and you find out its provenance.

Here’s what they look like:

Adult peregrines (2+ years old in October) have fresh plumage in charcoal gray and white.  The photo at top shows an adult male in flight.  The photo below is an adult female.  Adults have:

  • Solid dark charcoal helmet (head)
  • Dark charcoal malar stripes (on face)
  • Clean white or slightly rosy chest and throat
  • Horizontal charcoal+white stripes on belly and flanks
  • Gray back: Male’s is pale blue-gray.  Female’s is “muddy” gray.

Adult peregrine, Univ of Pittsburgh, 2017 (photo by Peter Bell)
Adult peregrine, Univ of Pittsburgh, 2017 (photo by Peter Bell)

 

Juvenile peregrines (6 months old in October) are the same size as adults but their colors are brown+cream.  Juveniles have:

  • Variable brown helmet with some cream-colored traces (head)
  • Brown malar stripes (on face)
  • Cream colored chest that’s striped all the way up to the throat
  • Vertical brown+cream stripes on belly and flanks
  • Brown back.
  • (Bonus!) Juveniles have cream-colored tips on their tails, visible as the sun shines through them in flight.

Juvenile peregrine in flight, Univ of Pittsburgh, 2012 (photo by Peter Bell)
Juvenile peregrine in flight, Univ of Pittsburgh, 2012 (photo by Peter Bell)

Above, a juvenile in flight.  Below a juvenile shows off the vertical stripes on his chest and belly.  His variable brown helmet with “eyes on the back of his head” and horizontal cream-colored line at his crown.

Juvenile peregrine falcon, Univ. of Pittsburgh, 2016 (photo by Peter Bell)
Juvenile peregrine falcon, Univ. of Pittsburgh, 2016 (photo by Peter Bell)

 

Sub-adults are 18 months old with nearly complete adult plumage except for a few juvenile feathers.  They began to molt into adult plumage last spring at 10-12 months old.  By October their few juvenile feathers are hard to see without a photograph.  They are ready to breed next spring.

Below, an 18-month-old peregrine named Spirit is in rehab at Medina Raptor Center in the autumn of 2014.  You can see her back is mostly gray with just a few brown feathers.  Her head shows faint traces of the juvenile cream colors.

18-month-old peregrine falcon, Spirit, in rehab at Medina Raptor Center, Nov. 2015 (photo by Kate St.John)
18-month-old peregrine falcon, Spirit, in rehab at Medina Raptor Center, Nov. 2015 (photo by Kate St.John)

For a view of sub-adult plumage in the spring, see these photos taken in March 2016 of a 10-month-old Juvenile Peregrine Falcon Transitioning Into Adult Plumage.

For additional tips, see Ageing Peregrine Falcons in the Field by Alex Lamoreaux at Nemesis Bird.

 

(all photos taken at University of Pittsburgh by Peter Bell … except for the peregrine on the glove, “Spirit” at Medina Raptor Center, photo by Kate St. John)

Fat in Winter, Thin in Summer

Northern cardinals in May and February (photos by Cris Hamilton)
Northern cardinals in May and February (photos by Cris Hamilton)

Why do birds look fat in winter and thin in the summer?  Have they lost weight?

No.  They’re trying to stay cool.

Underneath their smooth outer feathers birds wear down coats all year long.  The down keeps them especially warm when they fluff it out to hold more heat next to the skin.  This fluffing makes them look fat on cold winter days.

When it’s hot, they can’t take off their down coats so they force hot air out of the down by compressing their outer feathers.  This makes them look thin.

The cardinal on the left, above, is not the thinnest one I’ve ever seen.  Cris Hamilton took his picture in May when the temperature was pleasant.  He’ll look considerably thinner this month.

It’s just another way that birds cope with heat.

 

p.s. We think of down as white but on a northern cardinal it’s black.  Click here to see a northern cardinal’s body feather, called a semi-plume, black at the root and red at the tip.

(photos by Cris Hamilton)

Birds’ Beaks Are Air Conditioners

Song sparrow singing (photo by Peter Bell)
Song sparrow singing (photo by Peter Bell)

How do birds cope with heat?  They have several obvious ways and at least one we can’t see.

Like us, birds stand in the shade and bathe to cool off.  They also appear to pant — actually gular fluttering — but their hidden cooling method is a surprise. They use the nasal conchae (pronounced KONK eye) inside their beaks.

Nasal conchae are complex structures that moderate the temperature of inhaled air and reclaim water from exhaled air.  Birds that live in hot dry places would benefit from bigger, better conchae.

A study published in The Auk: Ornithological Advances in 2016 found just that.

Raymond Danner of UNC Wilmington and his colleagues used CT scans to display the internal beak structures of two subspecies of song sparrows. The specimens were collected in Delaware and Washington, DC.

Delaware and D.C. don’t seem to have different climates, but a bird of the dunes copes with a hot dry micro-climate compared to one that nests in a wooded inland park.

Indeed, as reported in Science Daily, the CT scans showed that “the conchae of the dune-dwelling sparrows had a larger surface area and were situated farther out in the bill than those of their inland relatives.”

Here’s a dune-dwelling song sparrow beak with elaborate air conditioning structures.

CT scan shows nasal conchae inside the bill of a Song Sparrow (photo credit: E. Gulson-Castillo and E. Sibbald via Science Daily)
CT scan shows nasal conchae inside the bill of a Song Sparrow (photo credit: E. Gulson-Castillo and E. Sibbald via Science Daily)

This extra internal gear means the dune-based song sparrows (Melospiza melodia atlantica) have larger beaks than their inland cousins.

I’ll admit I haven’t noticed the slightly larger beaks of the beach birds.  Have you?

 

(photo by Peter Bell)