Archive for the 'Bird Anatomy' Category

Oct 05 2016

Why Canaries In The Coal Mine?

Published by under Bird Anatomy

Station Officer John Scott holding a canary cage used in mines rescue training at Cannock Chase, UK (Image courtesy of the Museum of Cannock Chase. Copyright unknown)

John Scott holding a canary cage used in coal mines rescue training at Cannock Chase, UK (Image courtesy of the Museum of Cannock Chase. Copyright unknown.)

Today, a bird anatomy lesson.

You’ve probably heard the phrase “the canary in the coal mine” and know it refers to advanced warning of a danger.  In the centuries before air quality instruments, miners carried canaries in cages into the mines to detect carbon monoxide and methane before they reached dangerous levels for humans.

Why did we use birds to detect bad air? Why not some other small animal?

Birds are uniquely equipped to detect (and succumb!) to bad air because their respiratory systems are so efficient.  Here’s why.

Our lungs suck in air, exchange oxygen for carbon dioxide, and push it out.  This is slightly inefficient because some air remains in our lungs after we exhale.  If you’ve ever had “the wind knocked out of you” you know it feels awful to lose that residual air.

Action of the diaphragm (animation from BIO 378, Prof. Gary Ritchison, Eastern Kentucky University)

Human lungs and diaphragm (animation from BIO 378, Prof. Gary Ritchison, Eastern Kentucky University)


Birds’ lungs don’t expand and contract; they only perform the oxygen-CO2 exchange.  Instead birds have 7 to 12 air sacs that act like bellows, moving air in and out of the lungs and the body.  The air sacs (pink below) move air in only one direction through the lungs (dark blue below), pushing all of one breath out when the next one comes in.  No residual air!

Bird respiratory system, airsacs highlighted (image from Wikimedia Commons)

Bird respiratory system, air sacs highlighted (image from Wikimedia Commons)

Because the air sacs perform different functions, each air molecule takes 4 steps to pass through the bird’s body –> two in/out breaths.

1st Breath, Air molecule enters the bird.

1. Inhalation:  Molecule is sucked into the body by the posterior (back of the bird) air sacs
2. Exhalation: Posterior air sac pushes molecule into bird’s lungs

2nd Breath, Air molecule leaves the bird.

3. Inhalation:  Molecule is pulled out of the bird’s lungs by the anterior (front) air sacs
4. Exhalation: Anterior air sac pushes molecule out of the bird!

In this way, birds have more time to absorb oxygen from each breath and their bodies notice airborne poisons sooner than mammals do.

To put it all together, here’s a four and a half minute video that shows how it works.


One more amazing feat:  The thin walls of birds’ air sacs can extend into the hollow bones of their wings and legs.  They have extra places to store air!


(photo credits: Click on each image to see its original in context.
*Station Officer John Scott with canary cage used in coal mines rescue training at Cannock Chase, UK. Image courtesy of the Museum of Cannock Chase. Copyright unknown.
*Human lungs and diaphragm. Image linked from Bio 378, Lecture 10, Prof. Gary Ritchison, Eastern Kentucky University
*Bird respiratory system diagram from Wikimedia Commons.
*Video of bird respiration by Ammt Bio on YouTube


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Jul 28 2016

Drinking Techniques

Italian Sparrows in Bolzano, Italy (photo from Wikimedia Commons)

Sparrows take a sip in Bolzano, Italy (photo from Wikimedia Commons)

On Throw Back Thursday:

Like us birds drink more water in the summer heat.  Have you noticed they use different drinking techniques?  Some drink with faces down, others tilt their faces up.

These house sparrows appear to be using the face-down technique on a martini.  But wait!  The glass held ice cream and they’re picking at the remains.   So what do they really do?

Find out how birds drink in this vintage article from 2010:

Anatomy: How Birds Drink


(photo from Wikimedia Commons. Click on the image to see the original.)

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Apr 28 2016

The Catbird’s Coverts

Gray Catbird (photo by Alan Vernon from Wikimedia)

Gray Catbird (photo by Alan Vernon from Wikimedia)

This week gray catbirds (Dumetella carolinensis) came back to Pittsburgh from their winter homes in Central America.

I saw my first one in Schenley Park on Tuesday (April 26) and now I hear them every day, singing from the coverts in my neighborhood.  Here’s what they sound like:

“Covert” means “thicket” but it’s also an ornithological term for feathers that cover the base of the main flight or tail feathers.

Gray catbirds have rust-colored undertail coverts.  Read about them in this 2010 bird anatomy lesson: Undertail Coverts.


(photo by Alan Vernon in Wikimedia Commons. Click on the image to see the original)

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Oct 14 2015

Math Comes In Handy

Published by under Bird Anatomy

Monk parakeets in a dispute (photo by Greg Matthews courtesy NIMbios press release)

Monk parakeets arguing (photo by Greg Matthews, courtesy NIMBios press release)

Imagine a group is thrown together in a new social setting and each member has to figure out where he stands.  You’ve experienced this.  Remember the first day of high school?

Humans work out their social hierarchy fairly quickly and quietly though, thinking back to high school, some people pick fights to establish dominance.

Like humans, monk parakeets (Myiopsitta monachus) also maintain a social hierarchy.  Researchers at the National Institute for Mathematical and Biological Synthesis (NIMBioS) wondered how the birds figured out their pecking order so they threw together two new flocks and watched what happened.

At first the birds had no hierarchy and quietly assessed each others’ rank without fighting.  After about a week the major rankings had shaken out and some of them started to fight.

For 24 days the humans kept track of the parakeets’ interactions, carefully noting who fought and who won.  Interestingly, many birds didn’t fight and even those who did seemed to pick their battles.

Analysis of more than 2,300 interactions showed that the parakeets kept track of who won and lost and extrapolated the rankings to figure out their nearest competitors and those not worth challenging.  They only bothered to fight if they were close in rank and couldn’t determine it by extrapolation.  For example,

Able and Charlie know they’re both stronger than Baker (no fight necessary) so they must be roughly equal but don’t know who’s best unless they fight … except …

Dirk beat up Able yesterday and Charlie beat Dirk.  By inference, this makes Charlie better than Able.  After only two fights the pecking order is:  Charlie > Dirk > Able > Baker.

This kind extrapolation involves a lot of math (logic) and is much harder to do in large groups but the birds are so smart that they avoid fights by doing the math in their heads.

Math comes in handy, even in social settings. There’s a good reason it’s taught in high school.  😉


Read more here at Science Daily.

(photo by Greg Matthews, courtesy National Institute for Mathematical and Biological Synthesis press release)


p.s. For more information on why monk parakeets fight, see this blog from  Why Exactly Do Monk Parakeets Fight

p.p.s. Monk parakeets (also called Quaker parakeets) are “agricultural pests” in many states.  In Pennsylvania they’re illegal to own and are removed when found in the wild.  This is not the case in New York where monk parakeets hang out near JFK Airport, as shown in Gintarus Baltusis’ photo below.

Monk parakeets near JFK airport (photo by Gintaras Baltusis)

Monk parakeets near JFK airport (photo by Gintaras Baltusis)

Can you see this group doing math?


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Sep 02 2015

No Feet

Published by under Bird Anatomy,Songbirds

Hummingbird foot, in bander's hand (photo by Kate St. John)

Leg and foot of ruby-throated hummingbird in bander’s hand (photo by Kate St. John, bander Bob Mulvihill)

Here’s the leg of a ruby-throated hummingbird, so short that the toes make up nearly half its length.

Look closely and you’ll see the foot resembles a garden claw.

Garden claw tool (illustration from

Garden claw (illustration from


This group of birds also has tiny feet shaped like garden claws.

White-throated swifts (Crossley ID Guide for Eastern Birds via Wikimedia Commons)

White-throated swifts (Crossley ID Guide for Eastern Birds via Wikimedia Commons)


Once you know their feet are similar, it’s not a big leap to realize that these birds are related.

Swifts (Apodidae) and hummingbirds (Trochilidae) are in the same the taxonomic order Apodiformes, a Greek word that means “A”=no, “pod”=foot.

“No feet.”  🙂


p.s. Click here to read more about the similarities between hummingbirds and swifts.

(hummingbird photo by Kate St. John, garden claw clip art from, white-throated swifts illustration from the Crossley ID Guide for Eastern Birds, Creative Commons license, via Wikimedia Commons. Click on the images to see the originals)

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Sep 01 2015

Strong Opening

Published by under Bird Anatomy,Songbirds

Immature blue-winged warbler shows beak-opening strength at Neighborhood Nestwatch banding (photo by Kate St. John)

Immature blue-winged warbler shows its strong opening muscles, in bander’s hand (photo by Kate St. John, bander Bob Mulvihill)

With songbird migration underway, here’s something to think about when you see a blue-winged, golden-winged, Tennessee, orange-crowned, or Nashville warbler:  Their beaks make a strong opening.

Back in July at Cunkelman’s Neighborhood Nest Watch banding, Bob Mulvihill’s mist nests captured an immature blue-winged warbler (Vermivora cyanoptera).  With the bird in hand he put his fingers lightly on the bird’s beak and it immediately opened its beak and pushed Bob’s fingers away.  What an unusual talent!  These warblers have extremely strong gaping muscles.

Golden-winged warblers, closely related to blue-wings, are so well studied that this fact is mentioned in the literature about them.  Bob has also found it to be true of the (formerly*) Vermivora warblers and oriole species he’s banded in eastern North America.

Why this unusual talent?  Vermivora literally means “worm eater” — vermi:worm, vora:eat.  The “worms” are small caterpillars (not earthworms) that hide among leaves, often wrapped in cocoons or in curled up leaves.  The warblers open the rolled leaves against the caterpillars’ will.

When you see these talented birds watch them probing among the leaves.  They’re making a strong opening.


(photo by Kate St. John)
And what’s all this about formerly(*)?
The genus Vermivora used to contain nine species including Tennessee, orange-crowned, Nashville, Virginia’s, Colima and Lucy’s warblers, but in 2010 the American Ornithological Union transferred all but Bachman’s (extinct), blue-winged and golden-winged to the genus Oreothlypis.  After years of having nine Vermivoras, it’s hard to keep up with the changes.

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Aug 18 2015

Small and Belligerent

Male ruby-throated hummingbird in bander's hand (photo by Kate St.John)

Male ruby-throated hummingbird in bander’s hand (bander Bob Mulvihill, photo by Kate St.John)

Now that the breeding season is over and dry weather is suppressing native flowers, ruby-throated hummingbirds are swarming to backyard feeders in Pennsylvania.  All of them are small and feisty, but did you know the males are even smaller and more belligerent than the females?

Ruby-throated hummingbirds are sexually dimorphic in size though they’re all so tiny that only a bander could know.  At banding, birds are weighed and measured and so we’ve learned that male ruby-throats are about 87% the size of females in wing length and weight(*).  Their size is related to their lifestyle.

Female ruby-throated hummingbird in bander's hand (photo by Kate St.John)

Female (or is this an immature?) ruby-throated hummingbird in bander’s hand (bander Bob Mulvihill, photo by Kate St.John)

Male hummingbirds are the original deadbeat dads.  Ruby-throated males rush north in the spring to claim territories with lots of food which they vigorously defend with aerial displays, chasing, and bill-to-bill sword battles.

When a female shows up the male doesn’t welcome her at first (he acts annoyed) but he switches to intensive courtship displays when she perches.  Good hovering technique really impresses her and to do it well he needs lots of energy, smaller wings, and a lighter body than hers — which he has.

As soon as he’s mated with one lady he looks for the next.  He never helps with nesting and young and is so focused on attracting another female and warding off other males that he may forego feeding for much of the day.  Banders have found that adult males lose weight in June and July, though they regain it in August.

By the end of the breeding season there are noticeably fewer adult males than females at bird banding stations.  In a study done at Powdermill Nature Reserve, Bob Mulvihill and Bob Leberman found that the adult sex ratio is most skewed in the fall when there are 4.1 adult females for every 1 adult male.

Their paper(*), published in The Condor in 1992, describes why more adult males die in the summer than at other times of year:

“As a species, the Ruby-throated Hummingbird is near the extreme of small size that is physiologically possible for an endothermic vertebrate. It is conceivable that males approach a critical body mass during the summer.  Below this critical mass they may have to abandon nocturnal homeothermy for hypothermic torpor, and may starve overnight or during periods of inclement weather.”

Male ruby-throated hummingbirds are so small and belligerent that it shortens their lives.


(photos taken at the Neighborhood Nestwatch bird banding at Marcy & Dan Cunkelman’s by Kate St. John, 18 July 2015.  Bob Mulvihill is the bander holding the birds.)
(*) The paper by Robert S. Mulvihill and Robert C. Leberman is entitled A Possible Relationship Between Reversed Sexual Size Dimorphism and Reduced Male Survivorship in the Ruby-throated Hummingbird, published in The Condor 94: 480-489.  It’s available as a PDF here at Sora.  Their work is cited in the ruby-throated hummingbird account at Cornell’s Birds of North America.

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Jul 20 2015

Yellow Shoulders

Published by under Bird Anatomy,Songbirds

Male American goldfinch, two years or older, at banding (photo by Kate St. John)

Male American goldfinch, two years or older, at banding (photo by Kate St. John)

Here’s something we learned at the Neighborhood Nestwatch banding at Marcy Cunkelman’s last Saturday that you won’t notice through binoculars.

Did you know that first-year male American goldfinches look different than the older males?

Full adult males, two years and older, have bright yellow shoulders (scapulars) that match their backs as shown above.  First-year males have a mix of black and yellow on their shoulders.

Here’s a first-year male held by the National Aviary’s Bob Mulvihill while he explains the color.

First-yearmale American goldfinch, at banding (photo by Kate St. John)

First-yearmale American goldfinch, at banding (photo by Kate St. John)

And here’s a side-by-side comparison of the scapulars: full adult on the left, first-year male on the right.  Notice how the younger male has black under the yellow on his shoulder.

Scapulars on 2-year+ male American goldfinch compared to 1st-year male on the right (photo by Kate St. John)

Pure yellow scapulars on 2-year+ male American goldfinch (left) compared to black+yellow on 1st-year male (right) — photo by Kate St. John

First-year males are old enough to breed but they don’t have any experience yet.  Perhaps the ladies use the colors as a signal when picking mates.

If you look closely for the yellow shoulders, you too can separate the men from the boys.


(photos by Kate St. John)

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Feb 19 2015

TBT: Cold Feet

Mourning Dove in winter (photo by Marcy Cunklelman)

Throw Back Thursday (TBT)

Unlike many birds, mourning doves are prone to frostbitten toes.  Can they do anything to avoid it?

Last Sunday morning when it was 2o F, two mourning doves flew in to stand on the dry patch in my heated bird bath.  They were warming their feet!

This morning it is zero degrees Fahrenheit so I expect they’ll be back.

Here’s why they need to warm their toes in an article from January 2010:  Cold Feet.


(photo by Marcy Cunkelman)

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Feb 08 2015

Both Male And Female

Published by under Bird Anatomy

Bilateral gynandromorph northern cardinal (photo courtesy Western Illinois University)

Bilateral gynandromorph northern cardinal (photo courtesy Western Illinois University)

This northern cardinal has a birth defect that made it both male and female.  The right side of its body is female, the left side is male.

This cannot happen in humans because our sexual characteristics are determined by hormones but in birds each cell has a sexual identity that’s determined early in embryonic development.

On rare occasions something goes wrong during the first cell division and an individual bird is born a bilateral gynandromorph.  In other words, side-to-side (bilaterally) exactly half the body is female (gyn) and the other half male (andro).  The dividing line is always vertical from head to tail.  To understand how this happens, read this 2010 blog post on bird chromosomes: Anatomy: W and Z

In bird species where males and females look the same it’s hard to tell this has happened but in sexually dimorphic species like the northern cardinal or evening grosbeak, it’s easy to see.

This particular cardinal from Rock Island, Illinois is now famous because he-she was studied extensively by Professor Brian Peer and Robert Motz of Western Illinois University.  Their findings — “Observations of a Bilateral Gynandromorph Northern Cardinal (Cardinalis cardinalis)” — were recently published in The Wilson Journal of Ornithology and featured in Science magazine.

Click here to see the press release at Science Daily.


(photo courtesy Western Illinois University)

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