Class Aves. Classfication of 🐦 Birds into orders with examples. For Bsc Zoology.(Miller and Harely) скачать в хорошем качестве

Class Aves. Classfication of 🐦 Birds into orders with examples. For Bsc Zoology.(Miller and Harely)

General Characteristics of Class Aves: Some of the general characters of class Aves the birds are listed below: 1. Birds are bipedal feathered and warm blooded (homoiothermous) animals i.e., they are able to maintain a constant body temperature. Their fore-limbs are modified into wings. Most of them can fly except flightless birds (e.g., Ostrich). Class Aves has about 9000 species. The hind-limbs are adapted for perching, walking or swimming, etc., and usually bear four, sometimes three and rarely two toes. 3. Except uropygium gland (preen gland or oil gland), at the base of the tail, no skin gland is present. Ostrich and parrot lack oil gland. 4. The upper and lower jaws are modified into beak, which lacks teeth. Beaks are adapted to many ways of feeding; seed-crushing, fruit-scooping, flesh-tearing, nector-sip- ping, wood-chiselling and so on. 5. Legs are modified for walking, hopping, grasping, perching, wading and swimming. Legs bear homy epidermal . The alimentary canal has additional chambers, the crop and gizzard. The crop stores and softens the food; however, the gizzard helps in crushing and churning the food. There is a cloacal aperture. Gall bladder is absent in some seed-eating birds (graminivorous) such as pigeons. single left ovary and oviduct. If right ovary and oviduct are present, they are vestigial (nonfunctional). 15. Many birds show sexual dimorphism. All birds are oviparous. Like reptiles birds lay cleidoic eggs which are macrolecithal and calcareous. Four embryonic membranes (e.g., chorion, amnion, allantois and yolk sac) are formed. 16. The birds are the most beautiful among the animals. They show courtship, nest building, parental care, migration and territorial behaviour. Flight Adaptations in Class Aves: 1. Spindle-Shaped Body: ADVERTISEMENTS: It is designed to offer minimum resistance to the wind. 2. Feathers: They provide the passage for air and reduce friction to minimum. They also prevent loss of heat and help to maintain a constant temperature. 3. Wings: ADVERTISEMENTS: Fore-limbs are modified into wings, which help during flight. 4. Beak: Besides procurement of food, the beak is also used for nest-building. 5. Neck and Head: Mobile neck and head are very useful for feeding, nest building, offence and defense. 6. Flight Muscles: The flight muscles on the breast are greatly developed which help in flight. 7. Hind Limbs (Legs): They are well suited for perching. 8. Endoskeleton: Most of bones are pneumatic and filled with air instead of bone marrow. It makes the body light. Most of bones are firmly fused together, which help in flight. 9. Air Sacs: These are attached to lungs which serve as reservoirs of air. They may also aid as cooling devices in regulation of the temperature of the body. 10. Warm-Bloodedness: Birds are warm-blooded animals which is necessary for flight. 11. Circulatory System: A large oxygen supply is required for rapid metabolism and warm-bloodedness. It is done by an efficient circulatory system. 12. Absence of Urinary Bladder: Except Rhea, urinary bladder is absent in birds. Excreta are passed out at once. This helps in reducing the weight of the body. 13. Brain and Eyes: Brain and eyes are well developed. Equilibrium is maintained by well developed cerebellum of the brain. 14. Single Ovary: Presence of a single functional ovary on the left side in the female bird also leads to reduction of weight which is so essential for flight. Classifications of Class Aves: Class Aves is divided into two subclasses: Subclass I. Archaeornithes: Extinct, toothed beak, tail long  . The alimentary canal has additional chambers, the crop and gizzard. The crop stores and softens the food; however, the gizzard helps in crushing and churning the food. There is a cloacal aperture. Gall bladder is absent in some seed-eating birds (graminivorous) such as pigeons