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The Unique Characteristics of Birds


What makes a bird...a bird?

We have all seen birds...they are everywhere, in our backyards, gardens, and hedgerows. You can even find birds in cities. They bring life and color to our world, as well as beautiful songs and sounds! But what, by the technical definition, is a bird? Biologists like to classify organisms into groups, and if you enjoy birding, you probably like to classify too (I know I do).

This lens seeks to answer the question "what is a bird?" by outlining the physical characteristics that are unique to birds and the Class Aves. Together, these characteristics identify birds as a monophyletic group. You may be surprised to learn that the two features most commonly associated with birds, flight and feathers, are not entirely unique to birds! Bats are mammals that can fly and some dinosaurs had feathers. :)

Hint: there may be a quiz at the end!

(Photo: the beautiful mug of a King Vulture, courtesy Flickr Creative Commons)

Clickable table of contents for this page:

Bird Topography - from Wikimedia



All living birds have feathers, and no other animal alive today has feathers. However, feathers are not completely unique to birds. Did you know that some dinosaurs had feathers? However, since there are no living feathered dinosaurs, we can say that feathers are a unique characteristic among birds today.

Feathers can be found in just about every color imaginable! All of a bird's feathers collectively are called its plumage. Feathers are not only used for flight, they actually have many purposes, including: attracting mates, territorial dominance, regulation of body temperature, camouflage, and flight. There are also many types of feathers which serve different functions. The four main types of feathers are semiplumes, filoplumes, bristles, and powder.

More about bird feathers!

The Wonder of Bird Feathers


Horny Beak

Toothless in modern birds

The jaws of a modern bird are covered with a horny sheath --- which means birds have what's known as a horny beak. Many early birds had teeth, but no modern birds do. Why? Birds need to be as light as possible in order to fly effectively and teeth would add weight to a bird's skull. Also, a horny beak is much lighter than bone.

Many bird species have a bill that is specialized, which enables a particular bird to eat certain foods. Raptors have a hooked bill for ripping and tearing meat, seed eaters have a heavy bill for crushing seeds, and hummingbirds have a long narrow beak for sucking nectar from flowers. These are only three beak adaptations, there are countless others!

The Bird's Bill or Beak

Bird Beak Adaptations - Pictures

Roseate Spoonbill and its amazing bill shape (Image: wikimedia commons)

Bird Bill Shapes

Bird Bill Shapes

Bird Bill Shapes

My favorite bird field guide



Commonly called the WISHBONE

We've probably all played the game at one point in our lives --- two people grab hold of either tail of a wishbone (usually from a turkey) and give a tug. The person who comes up with the largest half gets to make a wish! But what really is a wishbone and do other animals have them? A "wishbone" or furcula is actually two fused clavicles. Other groups of animals have clavicles, but not furculas. We call our clavicles collarbones. No other living animals aside from birds have a furcula, but some dinosaurs did.

Why do birds have wishbones? Like many features of the bird's anatomy, the furcula is an adaptation for flight. When a bird flies, the furcula acts as a little spring to help power the flight strokes and is also believed to help birds breathe during flight. Because it is a characteristic unique to birds, all birds have a wishbone --- even birds that do not fly.

More on furcula function.

Pelican Preening

Image: Flickr Creative Commons via Dwayne Madden

Fastest bird (and animal) on the planet


Pneumatic Bones

Commonly called Hollow Bones

Birds that can fly have some pneumatic or hollow bones. Some of the pneumatic bones in flighted birds include: the pelvic girdle, some ribs, the humerus, and the femur. Hollow bones do not contain marrow --- the bones have air-filled canals and are strengthened by criss-crossed struts. Some flightless birds, including penguins and ostriches, have only solid bones. Some dinosaurs also had pneumatic bones.

In order to fly birds need to have a lightweight skeleton. A large number of heavy, marrow-filled bones would prevent birds from flying, which is why hollow bones are such a useful adaptation. Another flight adaptation is the fusion and shortening of certain bones in the bird's skeleton, which also reduces weight. We see this in bats as well.

More information on the bird skeleton.

The Avian Skeletal System

Great Horned Owl in flight (notice the gopher in its right-hand talons)

Image: Flickr Creative Commons via Anita Ritenour

The Hallux - A special toe


Another characteristic unique to birds is the hallux.

What on earth is a hallux? It is just a special name for a bird's big toe! Most birds have a backward facing first digit (the hallux) and three forward facing digits. In most birds, the hallux can be used to grasp perches and other things. Not every bird has a useful hallux though, birds that only fly occasionally (like chickens) have a hallux that is farther up on the leg and never touches the ground --- otherwise this special big toe would slow these birds down when they run. Other birds, like woodpeckers, have two toes that face forward and two that face backward, this enables them to cling to vertical surfaces.

The claws on a bird's feet are actually specialized scales. Claws grow constantly and are kept short from daily use. Raptor claws are usually called talons.

Bird Feet

More on bird feet


Air Sacs

Most birds have nine

Birds do not have a diaphragm like mammals. Instead, birds have air sacs! Air is moved in and out of a bird's respiratory system through pressure changes in the air sacs. The air sacs act as bellows, when they expand air rushes in! A bird's air sacs even extend into some of its bones --- the humerus, femur, vertebrae, and skull. Air sacs also help to keep birds cool by expelling heat, this is useful because birds do not sweat. Again, this characteristic is unique to birds.

Thanks to air sacs, a bird's respiratory system is more efficient than the mammalian respiratory system, meaning birds can transfer more oxygen with each breath. Birds do have lungs, which are also much more efficient than a mammal's lungs, but a bird's lungs are different in many ways.

Bird Breathing

Bird Respiratory System

Few birds can rival vultures when it comes to soaring. This is a Turkey Vulture seen drying its dew-dampened wings in the morning sunlight. These birds are capable of soaring for hours on thermals (rising columns of warm air).

Image: Flickr Creative Commons via Anita Ritenour

Other Bird Characteristics - While these traits may distinguish birds from many other animals, most of them are not unique.


1. Fusion and reduction of bones

2. Flight (Most. Flightless birds are called Ratites.)

3. Songs and/or calls

4. Egg-laying

5. Small size

6. Bipedalism (digitigrade foot posture)

7. Forelimbs modified for flight

8. Endotherms (commonly known as "warm-blooded" meaning birds maintain their body temperature through metabolic heat)

9. Single aortic arch which bends right (this is UNIQUE)

Image: Doug Wheller via Flickr Creative Commons.

Did you learn something from my lens? - American Robin


Purple Star!!!

This page was awarded with a Purple Star for quality content on 7 July 2011. Thank you to my readers, nominator, and Robin!!! (:

So I can visit some of your lenses! :D

Please sign my guestbook!

Laura Hofman from Naperville, IL on July 11, 2013:

Very interesting and informative lens! I learned a lot and enjoyed your beautiful photos.

norma-holt on December 31, 2012:

A new blessing on this lovely lens and may you have a wonderful, successful and happy 2013. Hugs

Pat Goltz on October 12, 2012:

Very informative page overall. Hate to break it to ya, though. Archaeopteryx wasn't a dinosaur, but a bird. I don't know of any dinosaurs with feathers. Most scientists now agree Archaeopteryx is a bird.

boa11kfh on September 02, 2012:

nice lens - I never knew what a furcula was till now.

fireauthor on August 04, 2012:

very nice,thank you

gypsyman27 lm on July 17, 2012:

Very informative and interesting, well done. See you around the galaxy...

TheGourmetCoffe on July 15, 2012:

Birds are amazing, God's creation is awesome indeed. Really liked your lens, very well done and educational. Thank you for sharing your insights. Also "liked" it!

intermarks on July 01, 2012:

This is really educational. Many things can be learn in this lens.

norma-holt on May 28, 2012:

An amazing lens. Got 100% in the quiz so I must have been really taking notice of all your fabulous information. Featured on Blessed by Skiesgreen 2012-2 and also on Why are There Trees. Hugs

anonymous on May 26, 2012:

Flew back with some fresh angel dust.

Melody Lassalle from California on May 20, 2012:

Excellent lens! I learned many new things about birds. I will never look upon the regular birds in my area as common.

supersiva on May 19, 2012:

Splendid and detailed description about birds

desa999 lm on May 08, 2012:

Beautiful lens with great photos and comments.

anonymous on April 16, 2012:


sousababy on March 25, 2012:

Pinning this lens . . hope it helps!

SteveKaye on March 15, 2012:

Hello again, I came back to bless this lens.

Mary Crowther from Havre de Grace on January 16, 2012:

Love this lens! Very informative and interesting!

mannasugar on January 07, 2012:

Highly educational...A+...keep making Lens'....

SteveKaye on January 01, 2012:

Excellent Lens. Thank you for posting this and showing what can be done on Squidoo. Steve

EileenSmith LM on December 24, 2011:

Holy crap, SO COOL! Pneumatic bones! The-thing-I-never-knew-was-called-a-hallux! Air sacs! Legitimately learned a lot from this lens, so thanks for writing it.

sousababy on December 07, 2011:

You make learning about birds both fun and fascinating . . I needed a refresher and came back to google + 1 your work.

athensfever on November 12, 2011:

very well documented lens... great work!

ZazzleEnchante on October 18, 2011:

Wonderful lens, great videos, loved reading it. Blessed by a SquidAngel.

mrsphillips200 on October 04, 2011:

Cool lens. I was hoping that it would focus more on individual species like your prehistoric lens, but educational all the same.

pawpaw911 on September 17, 2011:

Liked the robin with babies photo.

Snakesmum on September 12, 2011:

Loved the pictures and video of the raptors. Learned some things too. Great lens.

anonymous on September 01, 2011:

Nice and information lens, I passed your quiz with 75%, a big thumbs up for you

reasonablerobby on August 22, 2011:

What a great lens, easy to read and packed full of interesting things.

JeanJohnson LM on August 08, 2011:

Very educational lens, there's plenty to learn about birds!

sukkran trichy from Trichy/Tamil Nadu on August 04, 2011:

wonderful presentation of bird education. ~blessed~

Renaissance Woman from Colorado on July 23, 2011:

This is such a fabulous lens. I learned a great deal. Thank you for teaching me so much. Congrats on your shiny new Purple Star! :-) You definitely earned it. **Blessed** by this Squid Angel.

khellogs on July 22, 2011:

You deserve purple star for this lens! great job!

uruha-fan-girl on July 17, 2011:

Its interesting that there are so many different birds with different feet, beaks, different eating habits. I actually didn't know that there were that many! ha ha Nice Lens^ ^

anonymous on July 12, 2011:

I love birds - and I aced the quiz. Yay! :) Thanks for the fun lens.

anonymous on July 10, 2011:

Dear lady Jenna.. This one of my most favorite lens that I really love :) Congratulations and give you another 5 wonderful stars from me to you ;) You bird explaining with beautiful writing and videos make people here a big smile :D Tweeted to all my fans. Have a wonderful time.. always.. dear lovely lady :)

Nancy Tate Hellams from Pendleton, SC on July 10, 2011:

Congratulations on your well deserved Purple Star. I sure enjoyed reading this and learning about the Unique Characteristics of Birds. Thanks.

ColorPetGifts on July 10, 2011:

What a fun lens, congrats on your purple star -:)

NoYouAreNot on July 10, 2011:

Very educational and well-structured and presented. Congratulations on your purple star.

pimbels lm on July 10, 2011:

Congratulation on your purple star. I enjoyed reading this lens, very interesting. Thank you.

sousababy on July 09, 2011:

Congrats on your well-deserved purple star! You certainly have earned it . . wishing you many, many more accolades both on and off Squidoo.



Ramona from Arkansas on July 09, 2011:

Wonderful!!! I love birds. I even own one - Quaker Parrot. I've raised baby Robins once. That ws an experience I'll cherish forever.

AsianMarketplace on July 08, 2011:

Excellent and congrads for the purple star!

gogolf162 on July 06, 2011:

Great information. My brain is about to explode!

pheonix76 (author) from WNY on June 27, 2011:

@sousababy: Thank you very much Rose!

wilddove6 on June 25, 2011:

Outstanding lens! I've taken the Cornell Lab of Ornithology Bird Biology've got everything here for the basic understanding of "what is a bird?". Fantastic!

sousababy on June 10, 2011:

I put this excellent lens of yours in the right sidebar of my lensography so people (like me) can get a really decent introduction to bird watching. Thank you so much. Fondly, Rose

sousababy on June 05, 2011:

This is really very explanatory. I found it easier than flipping through a bird guide book. I loved the way you showcased all the different parts (on different birds). Great photos, diagrams and easy-to-understand definitions. Great lens, something that would help any birdwatcher.

whoisbid lm on May 28, 2011:

Some people might also be interested to know why there are so many birds used in hieroglyphics. Thanks for this info!

Jerrad28 on May 26, 2011:

Great lens! Thanks for the cool info

redpillpuppet on May 24, 2011:

Wonderful lens! Great info and pics. I recently talked with someone who is absolutely horrified of birds which is hard for me to understand. Just wanted to share. :)

pheonix76 (author) from WNY on May 19, 2011:

@anonymous: Glad you like the quiz, thanks for the suggestion. :)

anonymous on May 18, 2011:

Blushing! I just noticed my rating was missing from my last visit here, just the favorite. I must have favorited too soon after rating, fixed!

anonymous on May 18, 2011:

I love the quiz you added here but missed one because I didn't review.

anonymous on May 17, 2011:

I was glad to learn that birds have a toe that is supposed to go backwards, There are some black birds fleding in my backyard and noticed one had a toe was backwards. Should have figured it out myself, it makes sense when you think about it. I love watching birds but usually do get close enough to see toes. Thanks for all the info.

anonymous on May 13, 2011:

Awesome lens, Jenna! Great work. :-)

Diane Cass from New York on April 28, 2011:

Great lens. I am an avid birdwatcher and benefactor of my backyard birds. My favorite field guide for birdwatching is the one from National Geographic. I love how it is organized, with the maps and bird info all on the same page. Thanks for a great read.

Ann from Yorkshire, England on April 24, 2011:

well put together, thanks for sharing

Stonecutter on April 22, 2011:

I guess I never gave a lot of thought to a lot of bird characteristics. This is some great stuff. Right now I have a page open all of the time that has a tree cam watching some bald eagles, their eggs hatched about a week ago and it is amazing how fast the eaglets are growing. Mom and dad are getting worn out getting chow for the three of them.

anonymous on April 20, 2011:

This is amazing! I was surprised at every turn how much I didn't know about how specially and specifically birds are designed....claws are made of scales, the wishbone is a fused clavicle and unique to birds (and some dinosaurs), bones are hollow, their respiratory system is complex and unique......I have never learned so much in such a short amount of time or been so in wonder learning! Beautifully done from start to finish, in fact, I was disappointed we were done. Oh, and that Peregrine Falcon video reminded me of something I heard on TV years ago by a guy how loved them, "Peregrines fly, other birds flap". I'm going to have get this gem lenrolled an featured on my Bald Eagles lens, pronto!

sukkran trichy from Trichy/Tamil Nadu on April 19, 2011:

well presented informative lens.

LadyFlashman from United Kingdom on April 16, 2011:

Fascinating fact and gorgeous photos too! I love love love this lens!

pheonix76 (author) from WNY on April 09, 2011:

@ElizabethJeanAl: I think that's the case with most birders....they enjoy looking, but know very little about anatomy and physiology. I was unaware of everything on this page until I took an ornithology class --- which opened my eyes to how much MORE there is to learn. Thanks for stopping by and enjoy the birds! :)

ElizabethJeanAl on April 09, 2011:

I love watching the birds but I haven't studied them as much as I would like.

Rob Hemphill from Ireland on April 08, 2011:

Such a lovely lens. Thoroughly enjoyed watching the Peregrine and Gos Hawk video.

Have lensrolled you to my African Birds, and thanks for the visit.

A RovingReporter on April 06, 2011:

You sure know about birds. Very informative lens. Thanks for sharing.

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