The Latin word Avis means bird. Vertebrate animals that have left water and land to take to the skies are called birds. Their bodies are adapted for flight and they have evolved as flying machines. The physical characteristics of the birds resemble those of archosaurs of the Mesozoic era. The total number of species is 10,000. 21 classes and 706 species of Avis class have been identified in Bangladesh. Dr. Siddiq Publications
Features of Avis
1. The body is covered with feathers and the forelegs are modified into two wings.
2. Their necks are elongated and S-shaped.
3. The jaws are toothless and have evolved into beaks.
4. Intraskeletal pores, bone hard, light and airy. Bones contain air-filled cavities.
5. Air sacs exist in the lungs. The sphincter consists of the syrinx, the organ that produces sound.
6. They are endothermic or warm-blooded animals. That is, their body temperature does not change with the rise and fall of the environment temperature.
7. The heart has four chambers, 2 atria and 2 ventricles.
8. Their digestive system consists of crop and gizzard. So able to digest energy food quickly. Dr. Siddiq Publications
9. The crown of the head is connected to the spinal cord by an occipital condyle. The sternum forms a boat-like keel.
10. They are bipedal and can fly.
11. Their feet have clawed toes.
12. They lay eggs. The egg hatches and the baby comes out.
13. Newborn babies are active and vigorous or naked and weak.
[key words to remember characteristics: feather, wing, neck, beak, air cavity, air sac, syrinx, endothermic, heart, digestive system, occipital condyle, keel, biped, toe, egg] Dr. Siddiqu Publications
Adaptation for successful flight adaptation
1. Their bodies are covered with feathers. The body is light and the feathers help to float in the air.
2. Their necks are elongated and S-shaped. So can lean forward easily.
3. They are bipedal animals. The forelimbs have evolved into wings. Wings are their main flight organ. Dr. Siddiq Publications
4. Jaws have evolved into beaks. It helps in flight.
5. Their bones are hard, light and airy. It reduces body weight and can fly easily. Dr. Siddiq Publications
6. They have air sacs in their lungs. Air sacs contain air. The body is light and can fly easily.
7. The heart has four chambers, 2 atria and 2 ventricles. So pure blood supply is ensured. Dr. Siddiq Publications
8. The sternum has formed a boat-like keel which aids in flight
Birds are called majestic reptiles
Birds evolved from reptiles during the Mesozoic Era. The ancestors of birds are reptiles. Reptiles have evolved into birds. In the early 20th century, the famous ornithologist Thomas Huxley called them birds as the majestic reptiles. Archeopteryx is a fossil link between reptiles and birds. That is, archeopteryx evolved from reptiles and birds evolved from archeopteryx. The characteristics of the creation of birds from reptiles are-
1. Reptiles are cold-blooded animals with low metabolic rates. Birds are high-blooded animals with high metabolic rate. Dr. Siddiq Publications
2. Reptiles are mobile animals. Birds can move faster due to the gain in flight ability.
3. Reptiles have dry fibrous bodies. Bird feathers have been created from the dung of reptiles. Dr. Siddiq Publications
4. The four-chambered heart of a bird has been created from the incomplete four-chambered heart of a reptile.
5. There are two systemic arches in the circulatory system of reptiles and one systemic arch of birds.
6. The renal portal system of reptiles is highly developed. It is decaying in birds.
7. The jaws of reptiles gave rise to the long beaks of birds.
The above discussion proves that birds have evolved from reptiles. That is, birds are majestic reptiles.
Some birds of Avis
Doyle – Copsychus saularis
Rooster – Galus galus
Owl – Bubo bubo
Eagle – Haliacetus leucogaster
Pigeon – Columba livia
Hummingbird – Mellisuga helenae
Dove – Streptopelia decaocto
Shalik – Lamprotornis hildebrandti
Cuckoo – Eudynamys scolopaceus
Buck – Nycticorax nycticorax
Passer domesticus
King vulture – Sarcogyps calvus
Black Pheasant – Francolinus francolinus
Quail – Coturnix coturnix
Moina – Gracula Religiosa
Tia – Psittacula krameri
Dahuk – Amaurornis phoenicurus
Crane – Grus antigone
Crow – Corvus splendens
Bulbul – Pycnonotus cafer
Ostrich – Struthio camelus
Peacock – Pavo cristatus
Babui bird – Ploceus philippinus
Pelican – Pelecanus philippensis