Comparative Anatomy

I was try­ing to decide what to write about next and I started to think about what make birds unique. There are many inter­est­ing anatom­i­cal dif­fer­ences and sim­i­lar­i­ties to mam­mals that most peo­ple don’t real­ize. Adap­ta­tions in anatomy allow birds to fly, migrate hun­dreds of miles, stay warm or cool in harsh envi­ron­ments, digest food that oth­ers may not be able to eat, talk and mimic like no other ani­mal, and the list goes on.
So here are some inter­est­ing anatom­i­cal facts:

  • Many birds have become asym­met­ri­cal to make them lighter and more effi­cient. For exam­ple, mam­mals have two jugu­lar veins that allow blood to flow from the head back to the heart and they are about the same size on both sides of the neck. Most birds have a larger ves­sel on one side of the neck than the other–often it is the right side that has a more promi­nent vein. Many female birds also have a  sin­gle oviduct or repro­duc­tive struc­ture with one ovary. This is usu­ally found on the left side of the body. Males do have two tes­ti­cles though.
  • Wings are amaz­ing struc­tures. Just like front leg/arms on a mam­mal, they have a humerus, radius and ulna (although the ulna is larger of the two bones in the bird which is oppo­site of humans), and a wrist joint and fin­gers or dig­its. Most of the wrist bones and bones that would be a hand are fused (carpals and metar­cara­pals) and they  have three digits–the alu­lar digit is sim­i­lar to the mam­malian thumb.

homology: homologies of the forelimb among vertebrates

  • Birds have air­sacs through­out their bod­ies. Imag­ine bal­loons that fill up with air, then the air passes to the lungs, then to another air sac, then back to the lung–thus allow­ing air to pass twice through the lungs for more effi­cient fil­ter­ing of oxy­gen. The air­sacs also extend from the body into the the wings and legs (humeri and femurs) and this allows these bones to be hol­low and lighter than those found in other animals.







  • Birds do have ribs and they have a keel. Any­one who has eaten a bird or prepped a meal has seen the large breast plate that is under the “white meat” or breast mus­cle. It is this bone and these mus­cles that allow the bird to expand the chest to breath. Birds do not have a diaphragm and thus all of their organs are in one cham­ber with no divi­sion. This is why it is so impor­tant to restrain a bird prop­erly. If you hold a bird two tight around the body and chest, they will not be able to breath.
  • Birds have two parts to their stom­achs. A sim­ple stom­ach called the proven­tricu­lus which has gas­tric juices and flu­ids for enzy­matic break­down of food. They also have a giz­zard or a ven­tricu­lus. This is a mus­cu­lar struc­ture that acts as a grind­ing organ to break down harder foods and seeds. Many peo­ple of pet birds assume they need to pro­vide grit (tiny peb­bles) daily for the birds so that the giz­zard can use this to help grind down hard foods. Pet birds do not need a daily dose of grit. In fact they need lit­tle if any to help with nor­mal grind­ing func­tion of the giz­zard. In fact, too much grit can lead to obstruction.

These are just a few of many dif­fer­ences.  After get­ting this far, I fig­ured I should post on this and then make addi­tional posts for more fun facts…otherwise I can just keep going and never it it on my page. So stay tuned…



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