Aves

Introduction:

• All types of birds are included in this class.
• Study of birds is known as "Ornithology".
• Dr. Salim Ali was the great ornithologist of India and regarded as "Birdman of India”
• Birds are also known as "Feathered bipeds or glorified reptiles".

Detailed explanation:
 

General characteristics of class Aves
 

Habit and habitat

• Aerial habitat
• Well adapted for flying.
• Though some birds are aquatic too.

Body

• Their bodies are boat shaped.
• It is divided into head, neck, trunk and tail.
• Neck is long and flexible.
• Body is covered with feathers or plumage.
• Forelimbs are modified into wings, which help in flying.
• Scales are found only on hind limbs.

Digestive system

• Digestive tract is complete and has additional chambers
• called Crop and Gizzard.
• Oesophagus is modified into Crop for quick food ingestion and storage.
• The function of Gizzard is crushing the food which is swallowed unmasticated.
• A three chambered cloaca is present in the birds.
• Pigeon or crop milk is secreted by both sexes (Crop product).
• Their jaws are modified into horny beaks or rhamphotheca, which are toothless.

Respiratory system

• Spongy lungs are present for respiration.
• Inelastic air sacs are found.
• Air sac is connected to lungs for supplement respiration.
• Sound producing organ at the junction of trachea and bronchi of birds is called syrinx.

Circulatory system

• Heart is four chambered.
• Double circulation is found.
• Hepatic portal system is well developed in birds, but the renal portal system is ill developed.
• Sinus venosus is absent.
• Only Right aortic arch is present.
• R.B.Cs are nucleated,biconvex and Haemoglobin filled.

Excretory system

• Kidneys are metanephric.
• Ureters open into cloaca.
• These are mostly Uricotelic.
• Most of the birds do not have a urinary bladder and copulatory organ.

Skeleton

• Bony endoskeleton.
• Monocondylic skull
• Body is covered by keratinised plumage,while hindlimbs have a covering on scales.
• Last four caudal vertebrae fuse to form pygostyle which helps in wagging of the tail.
• Long bones are hollow, with air filled cavities and these bones are called pneumatic bones.These make the body light in weight and help in flying.
• Sternum is large.
• Their swollen basal part of the sternum is called "Keel" which provides sites for attachment of flight muscles

Locomotion

• Forelimbs are modified into wings.
• Pectoralis muscles or flight muscles are well-developed for flying
• Hind limbs are best adapted for clasping the branches of trees or for perching or for walking and swimming.
• Two bones, clavicle and interclavicle fuse to form V - shaped bone called furcula or Wish bone or Merry-thought bone. It acts as a spring between two pectoral girdles.
• Pygostyle, Keel and Furcula are absent in flight less birds.

Nervous system

• Brain is large, smooth, highly developed.
• Cerebellum is well developed for aerial mode of life.
• Cranial nerves are 12 - Pairs.

Sense organs

• Dirhynous nose
• Olfactory organs are less - developed.
• Eyes are large and a nictitating membrane is present in the eye.
• Monocular vision
• A specific comb like structure, Pecten is found in the eyes of all birds except kiwi.
• Pecten helps in accommodation of the eye and provides nutrition to eyeballs. Acute vision and telescopic vision of birds is due to pecten.
• External ears are present but ear pinnae are absent. Only one ossicle columella (Stapes) is found in the middle ear.

Reproductive System

• Birds are unisexual.
• Sexual dimorphism is a characteristics feature.
• Birds are monodelphic i.e. only the left ovary and left oviduct is functional in females
• Fertilisation is internal.
• They are oviparous.
• Amniotes.
• Cleidoic eggs present.

Development

• Development is direct.
• All the birds from nests and Parental care is a characteristic feature.

Special adaptive features

• The characteristic features of birds are the presence of feathers all over the body and most of them can fly except flightless birds.
• Feathers keep them warm and also make body weight light.
• Feathers are modification of epidermal scales.
• They are warm-blooded (homoiothermous) animals, i.e., They are able to maintain a constant body temperature.
• Skin is dry and without glands but oil glands or Preen glands are found on the tail or Uropygium. These glands secrete oil, which lubricates feathers.
• Their vision is monocular.

Classification of aves
 

Class Aves is divided into two subclasses:
 

1. Archaeornithes.

• They are Extinct.
• Bones were non-pneumatic.
• Toothed beak
• Their tail is long lizard-like.
• Example - Archaeopteryx

2. Neornithes

• Modern as well as extinct birds
• Teeth are absent
• Tail is short.
• Example - Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture).

Common examples
 

1. Archaeopteryx (Lizard bird)

• They were extinct in the Cretaceous period.
• Its fossil was discovered by Andreas Wagner in 1861 from Bavaria (Germany).
• They are considered as the connecting links between reptiles and birds.

2. Aptenodytes

• They are commonly known as Penguin or "sea bird of Antarctica".
• Their forelimbs are modified into flippers for swimming.

3. Struthio

• They are commonly known as African ostrich or Camel-bird.
• It is the largest living bird of the modern period.
  
  
   

4. Rhea (American ostrich)

5. Apteryx

• They are commonly known as Kiwi.
• It is the smallest flightless bird.
• It is the National bird of New zealand.
• It has hair like feathers all over its body.

6. Pavo - cristatus

7. Psittacula



8. Columba livia

9. Passer domesticus

10. Peacock

• It is the national bird of India.

11. Humming bird or sunbird

• It is the smallest flying bird which is found in cuba.

Frequently Asked Questions: FAQs
 

Q1. Which scientist is regarded as the “Bird-man of India”?
Ans :

• Dr. Salim Ali was the great ornithologist of India and regarded as "Birdman of India”

Q2. What is the function of crop ?
Ans :

• Crop is found in birds for quick food ingestion and storage.
• In pigeon it is modified into crop glands for milk secretion.

Q3. What is the function of Gizzard ?
Ans :

• The function of Gizzard is crushing the food which is swallowed unmasticated.

Q4. What is the excretory product of birds ?
Ans : Uric acid

Q5. What is the voice box of birds called ?
Ans :

• Syrinx is called the voice box of birds which is present at the junction of trachea and bronchi of birds.

Q6. What are pneumatic bones?
Ans :

• Pneumatic bones are the long bones that are hollow, with air filled cavities.

Q7. Why are birds monodelphic ?
Ans :

• These condition is found to make their bodies light.

Q8. What is the hematopoietic organ of the birds?
Ans :

• Bursa of fabricius

Q9. What do you mean by Rhampothaeca?
Ans :

• Their jaws are modified into horny beaks or rhamphotheca, which are toothless.

Q10. What is plumage ?
Ans :

• They are used for the feathery coat for birds.