Write about aves.
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Question: Write about aves.
Answer:
- These are warm-blooded animals and have a four-chambered heart. They lay eggs. There is an outside covering of feathers,and two forelimbs are modified for flight. They breathe through lungs. All birds fall in this category.
Few examples are in the attachment.
Answer:
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.
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2. 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 scales.
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6. 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.
Respiratory System of a Bird
7. Respiration is by lungs. The lungs are spongy and inelastic. Air sacs are connected to lungs for supplement respiration. The larynx does not act as a voice box. Voice is produced by a special organ, the syrinx.
8. The heart is four-chambered. Sinus venosus is absent. Renal portal system is very much reduced. Red blood corpuscles are nucleated, oval and biconvex.
9. The kidneys are metanephric which drain the nitrogenous waste matter (chiefly uric acid) into cloaca through the ureters. Urinary bladder is absent except Rhea Americana (American Rhea— also called “South American Ostrich”. This is the only bird that has urinary bladder).
10. Brain is better developed than that of reptiles, of which cerebrum, cerebellum and optic lobes are quite large.
11. Birds have 12 pairs of cranial nerves.
12. Birds have a keen sense of sight but poor sense of smell but kiwi has good sense of smell. Pecten is present in the eyes of birds. Ear openings are present. Each ear consists of three parts: external, middle and internal.
13. Endoskeleton is fully ossified (bony) and the long bones are hollow with air cavities (pneumatic) to reduce weight. There is no bone marrow. The skull is monocondyllc, i.e., with one occipital