Category Archives: Bird Anatomy

From T-Rex To Hummingbirds

Chart of dinosaur-to-bird evolution (illustration by Steve Brusatte)

Ancient birds have a new family tree.

In a report last month in Current Biology researchers at University of Edinburgh and Swarthmore College analyzed 850 body features of 150 dinosaurs, then used statistical analysis to assemble a detailed family tree from dinosaurs to birds.

Interestingly, they found that the evolution of bird characteristics in dinosaurs was very gradual and non-linear.  Features like feathers, wings and wishbones appeared in many species over tens of millions of years so there is no "missing link" dinosaur line to the first bird.

"This process was so gradual that if you traveled back in time to the Jurassic, you'd find that the earliest birds looked indistinguishable from many other dinosaurs," said Swarthmore statistician Stephen Wang.

And then, 150 million years ago the bird skeleton came together and bang! there was an explosion in species from the one-of-a-kind hoatzin to more than 350 species of hummingbirds.  According to Science Daily, this explosion "supports a controversial theory proposed in the 1940s that the emergence of new body shapes in groups of species could result in a surge in their evolution."

Read more here in Science Daily about the family tree.

Most kids go through a dinosaur-loving phase.  Some of us fall in love with birds and never come out of it.  😉


(diagram by Stephen L. Brusatte, University of Edinburgh. Click on the image to see the original.)


Woodpecker Toes

Red-bellied woodpecker's toes, on banding day (photo by Kate St. John)

Here's a closeup of woodpecker toes from banding day at Marcy Cunkelman's last July.

Look at the direction of the toenails and you can you tell they belong to a woodpecker.  Two claws curl forward, two curl back.

Woodpeckers have zygodactyl feet that help them cling to tree trunks.

The other foot from the same red-bellied woodpecker shows his toes open -- two forward, two back.  Notice that the toes aren't all the same length.  The little toe is Toe #1, the hallux.

Red-bellied woodpeckertoes, foot open on banding day (photo by Kate St. John)


Most perching birds have three toes forward while the hallux points back: anisodactyl feet.  (You might recognize these toes from yesterday's Swainson's thrush photo.)

Feet of Swainson's thrush (cropped photo from Wikimedia Commons)

Anisodactyl is the most common form but there are four other arrangements of birds' toes.  Read more and see a diagram at this blog post from 2010.


(woodpecker photos by Kate St. John. Swainson's thrush feet are cropped from a photo on Wikimedia Commons. Click on the Swainson's toes to see the original photo)

Birds Can Recover Lost Hearing

Dr. Edwin Rubel works to restore human hearing by studying birds (photo from Univ of Washington Dept of Medicine )
Dr. Edwin Rubel studies chicks' ability to re-grow their hearing nerve cells. Univ. of Washington Dept of Medicine

My visit to an audiologist for a baseline hearing test revealed an awesome thing about birds.

This summer I had my hearing tested because I noticed I could still hear faint rustling sounds with my right ear but not with my left.  For a long time my left ear has been slightly "less good" but this spring was the first time I didn't have stereo for everything.  I was looking in the wrong direction for the very quiet birds.

The hearing test showed that my right ear is still above average but I've begun to age and am very slowly losing the top end of sound.  My left ear has lost more than my right -- hence the lack of stereo -- but for a human I have good hearing.  The sounds I've lost would only be noticed by a cat (or a birder).  Since those sounds aren't in the "human" range, the loss is not correctable.

But if I was a bird, I could correct it myself.

We hear thanks to tiny "hair cells" that line the cochlea of our inner ear.  Not "hairs" at all, they are actually protein-filled protrusions that vibrate when sound reaches them and transmit it electronically to the brain.  Age, loud noises, and toxins, including strong antibiotics, damage these cells.  Mammals cannot regenerate hair cells.  Birds can!

The photo above, from a 2004 article at the University of Washington's Department of Medicine, shows the man who discovered this with a bird that helped him prove it.  In the late 1980's Dr. Edwin Rubel at the University of Washington and Dr. Doug Cotanche at the University of Pennsylvania simultaneously discovered that birds can recover their hearing.  After hair cell loss they grow the hair cells back again!  Later research uncovered this same ability in fish.  (Click here for the 2004 UW article and here for information in the 2012 Hearing Journal.)

Their discoveries have led to work on a wide range of possible solutions, none of which are perfected yet.

For now, I compensate when I hear a faint bird sound -- I turn my head.

Some day, thanks to birds, there may be a cure for us mammals.


(photo of Dr. Edwin Rubel from a 2004 article about his research at the University of Washington Department of Medicine)

The Better To Eat With, My Dear

Immature red-bellied woodpecker shows his bony tongue (photo by Kate St.John)

During the Neighborhood Nestwatch banding at Marcy Cunkelman's last month I learned an amazing thing about the red-bellied woodpecker.  The tip of his tongue looks like a spear.

We saw this firsthand when an immature red-bellied shouted and displayed his tongue while he waited to be banded.

Here's a closer look.  You can see that his tongue is pointed and bony and coated with inward-facing barbs.

Red-bellied woodpecker has a bony tongue (photo by Kate St. John)

Not only is the tip of his tongue very specialized, but the entire tongue is extra long and easy to maneuver.  Under his skin, his tongue begins in front of his eyes and wraps over his skull to emerge in his mouth. This gives it enough slack that he can stick it out 1 to 1.5 inches beyond his bill.

This long maneuverable spear allows him to capture bugs and larvae in deep crevices.  He hammers the crevice, sticks out his tongue, maneuvers it inside the crack and stabs his prey.  If he doesn't completely spear it, no problem.  He has specialized mucus that makes his tongue sticky.

Click here to see an illustration and photo of the red-bellied's amazing tongue.

The better to eat with, my dear.


(photos by Kate St. John)

You Can See Her Egg!

Gravid female northern cardinal, held for banding by Bob Mulvihill (photo by Kate St. John)

We learned a lot about bird anatomy, at the Neighborhood Nestwatch banding on Saturday.  Did you know that ...

  • When you blow on the belly feathers of a songbird during the breeding season you see bare skin underneath.  This is the brood patch for incubating eggs and keeping nestlings warm.
  • Songbirds have translucent skin.  The red color is muscle under the skin, yellow is stored fat.
  • You can see the egg under the skin of a "pregnant" bird!

Even before he checked her belly, Bob Mulvihill could tell this female northern cardinal was gravid when he held her.   When he blew on her belly feathers we saw the white oval of the egg near her tail, circled below.

Gravid female northern cardinal, egg under skin (photo by Kate St. John)

This lady must have come out for breakfast before laying her egg and was delayed by the mist nets near the feeders.  She needed to get back to her nest soon(!) so Bob quickly banded, weighed and released her.  She immediately flew to the big maple and disappeared.

She weighed about 47 grams -- 5+ grams heavier than normal because she was carrying the egg.  That's a significant load to carry.

I hope she deposited it safely and that her morning turned out better than it began.  😮


(photos by Kate St. John)

Bird Skeletons As Heavy As Mammals’

Skeleton of wood grouse, Museum of Toulouse (photo from Wikimedia Commons)

A misconception that began with Galileo in 1683 was debunked four years ago but I've only just learned it now.  Perhaps this is news to you, too.

In the March 17, 2010 issue of Proceedings of The Royal Society B Biological Sciences, bat researcher, Elizabeth Dumont of the University of Massachusetts Amherst published her bird, bat and rodent bone density study and concluded:

Bird skeletons do not actually weigh any less than the skeletons of similarly sized mammals.  In other words, the skeleton of a two-ounce songbird weighs just as much as the skeleton of a two-ounce rodent.(1)

Elizabeth Dumont reached this conclusion by measuring the density of skulls (crania), upper arm bones (humeri) and thigh bones (femurs) of 20 families of perching birds, 11 families of rodents and 13 families of bats, all of them less than 400 grams.  The birds' bones were the densest.  Then she ran the numbers on skeletal bone mass and volume.

She remarked, "The fact that bird bones are denser than bones in mammals not only makes them heavier for their size, but it may also make them stiffer and stronger. This is a new way to think about how bird skeletons are specialized for flying and solves the riddle of why bird skeletons appear so lightweight and are still relatively heavy.

"This has never been explained fully and so has never gotten into the textbooks. I'd like to see that change."

So now we know.  Sorry, Galileo.

Read a (1)summary of the findings in Science Daily or the full article here in the Proceedings of The Royal Society B Biological Sciences.


(photo (flipped) of wood grouse skeleton at Museum of Toulouse by Didier Descouens, Creative Commons license, Wikimedia Commons. Click on the image to see the original. )

Staying Warm

Black-capped chickadee, common raven (photos from Wikimedia Commons and Shutterstock)

On this very cold morning everyone's working hard to stay warm but some have an easier time than others.  Who loses heat faster, the chickadee or the raven?

Just like us, birds burn calories no matter what they're doing.  However, birds have higher metabolic rates than mammals and require more calories for everything they do.  Any activity, from sleeping on an empty stomach to a burst of rapid flight, burns more energy than in vertebrates of a similar size.

Small birds have higher metabolic rates than large ones because of the relationship of surface to volume.  Heat dissipates from the surface of an object so the more surface there is, the greater the heat loss.  So, yes, the chickadee loses heat faster than the raven.  That's why northern animals are often larger-bodied than those who live in warmer climates.  Even among chickadees the black-caps in Maine are noticeably larger than the chickadees in Pittsburgh.

To stay warm the chickadees will look fatter today because they'll fluff their feathers to raise the loft of their down coats.  They'll also cover their legs to reduce heat loss and they will eat -- a lot! -- to replace the calories they're rapidly burning.

"Eat like a bird?"  Today all birds, and especially the little ones, are chowing down to stay alive.


(photo of Carolina chickadee from Wikimedia Commons. photo of raven from Shutterstock. Today’s Tenth Page is inspired by page 150 of Ornithology by Frank B. Gill.)

Not Born Like This

Black Skimmer (photo by Steve Gosser)

Speaking of pied shorebirds as I did yesterday ...  when I see American oystercatchers I'm reminded of black skimmers (Rynchops niger).  Both have bold black-and-white plumage and long beaks but their differences are striking.

Unlike oystercatchers, skimmers have very short orange legs and a beak whose mandibles are two different lengths.  They use their long lower mandible -- 2-3 cm longer than the upper -- to skim food from the ocean's surface in flight.  Click here to see.

Black skimmers aren't born like this.  At hatching their beaks are normal but by the time they fledge four weeks later their lower mandibles have grown 1 cm longer than the uppers, halfway to this striking adult appearance.

One more amazing beak fact:  Black skimmers' beaks look fat from the side but if you see them straight on they are knife-thin like this.

The better to skim with, my dear.


(photo by Steve Gosser)

Fancy Feet

Snowy egret feet (photo by Chuck Tague)

Monday's blog about identifying white wading birds got me thinking about snowy egrets' black legs and fancy yellow feet.  Wow!

Are there other birds in North America whose legs and feet are different colors?

The immature blackpoll warbler has them.  Adult blackpolls have bright orange-yellow legs and feet but the youngsters have black legs.  Their contrasting feet are a good identification tip during fall migration.  This one is wearing orange slippers.
Immature Blackpoll warbler (photo by Marcy Cunkelman)


Beyond the blackpoll I was stumped.  I searched my field guide page by page and discovered that golden-crowned kinglets have dark legs and pale yellow feet.  Who knew?  I never looked at their feet before.
Golden-crowned kinglet (photo by Shawn Collins)


Do any other North American birds have fancy feet?  I don't think so, but maybe you know of one.

In the meantime I'll leave you with this thought ...

Have you ever seen a Eurasian Coot?
Eurasian coot (photo from Wikimedia Commons)


(photo credits:  Snowy egret feet by Chuck Tague, immature blackpoll warbler by Marcy Cunkelman, golden-crowned kinglet by Shawn Collins, Eurasian coot from Wikimedia Commons)

House Sparrows Bulk Up

House sparrow molting, Sept 2008 (photo by Remi Jouan via Wikimedia Commons)

Have you noticed that a lot of birds are molting now?  On the extreme side I've seen a bald male cardinal and Mary DeVaughn reported a bald blue jay, both of whom shed all their head feathers at once.

Less extreme-looking but still ragged are the house sparrows.  Ten or more of them line up at my bird bath to splash wildly and loosen their old feathers.

Birds must molt to replace worn feathers but house sparrows, who don't migrate in North America, have an additional reason.  In August they put on heavier plumage that will keep them warm over the winter.

According to Ornithology by Frank B. Gill, the plumage on house sparrows weighs 0.9 grams in August.  By the end of September they're wearing 1.5 grams of feathers.

Our house sparrows are bulking up.

(credits: photo from Wikimedia Commons. Click on the image to see the original. Today's Tenth Page is inspired by page 154 of Ornithology by Frank B. Gill.)