General Characters of Birds (Aves)
· Arose from Reptilian ancestors in the Jurassic period.· Also called Feathered Reptiles or Glorified Reptiles.
· Homeothermic (Warm-blooded).
· Skin dry and covered with feathers. No glands on the skin except the preen glands on the tail.
· Jaws elongated to form beak or bill, teeth absent.
· Forelimbs are modified into wings.
· Bones pneumatic (spongy, light and hollow).
· Vertebrae heterocoelous and saddle-shaped.
· Skulls monocondylic. Sternum keeled.
· Synsacrum: formed by fusion of posterior thoracic lumbar, sacral and anterior caudal vertebrae.
· Pygostyle: formed by fusion of the last 3 or 4 vertebrae.
· Both clavicles and interclavicle fused to form a single furcula or merry-thought bone.· Respiration by lungs. Have 4-chambered heart, only right aortic arch present.
· Syrinx: Sound producing organ located at the junction of trachea and branchii.
· Larynx without vocal cord.
· Only the uropygial or preen gland is present in the skin but absent in all flightless birds except kiwi.
· Oesophagus is dilated to form crop for quick feeding and storage. Crop secretes pigeon milk.
· Kidneys metanephric, three-lobed. No urinary bladder. Ureters open into cloaca (3 chambered: coprodacum, urodacum, proctodacum).
· Uricotelic (Uric acid to conserve water) mode of excretion.
· Females have only left ovary and oviduct (Mullerian duct).
· Sexual dimorphism present. Fertilization internal. Oviparous.
· Amniota.
· 12 pairs of cranial nerves are present.
· Pectin is formed near the blind spot of the eye which help to provide the nutrition to eyeball but pectin is absent in kiwi.
Classification of Aves
The class Aves is divided into two sub-classes.1. Archaeornithes
2. Neornithes
1. Subclass- Archaeornithes
· It is extinct Jurassic birds of the Mesozoic era.
· They had teeth in both jaws.
· Tail was long lizard-like but wings were poorly developed and had little power of flight.
Examples: Archaeopteryx, Archaeornis
2. Subclass – Neornithes (Modern birds )
· Wings are well developed for flight mechanisms except few.
· Teeth are absent. The tail is short.
· Sternum is highly keeled.
Neornithes is divided into 4 orders
1. Order- Odontognathae
· Beak had teeth in extinct bird-like Hespeornis.
2. Subclass – Neornithes (Modern birds )
· Wings are well developed for flight mechanisms except few.
· Teeth are absent. The tail is short.
· Sternum is highly keeled.
Neornithes is divided into 4 orders
1. Order- Odontognathae
· Beak had teeth in extinct bird-like Hespeornis.
2. Order- Ratitae
· Flightless running birds. eg Kiwi
3. Order- Immpennae
· It includes penguins which are found in Antarctica and have paddle-like wings for swimming but are flightless.
· Marine and egg-lay in ice.
4. Order – Neognathae or Carinatae
· They are modern flying birds.
SOME IMPORTANT POINTS TO REMEMBER
· Ostium secretes dense albumin.· Magnum secretes white albumin
· Uterus secretes the calcareous shell
· Egg is Cleidoic, Macrolecithal and Telolecithal
· Cleavage is discoidal and meroblastic
· Amniota
· The copulatory organ is absent in all birds except Ratitae, Geese, ducks.
· Feather is formed by keratin protein.
· Feathers are three types - Quill feathers, Filoplumes and Down feathers
· Albatross (Diomedea) is the largest flying bird.
· Hummingbird is the smallest bird that can fly backwardly also.
· Swift is the fastest flying bird (60km/hr)
· Arctic tern is the long-distance migrant (11000 km)
· Cuckoo is a parasite bird that lays eggs in the nest of other birds.
· T. H. Huxley called birds are glorified reptiles
· Young called “Birds as masters of the air.”
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