🐦 Class Aves (Birds) – Key Features in Points

Body covered with feathers
Help in flight (lift and steering) and *prevent water/heat loss.
Endothermic (warm-blooded)
Generate heat from within through cellular respiration.
Maintain constant body temperature → called homeotherms.

Streamlined, spindle-shaped body
Reduces air resistance during flight.
Forelimbs modified into wings
Adapted for flying.
Bones are hollow (have air spaces)
Make body lightweight for flight.
Beak or bill replaces teeth
Made of keratin, lighter than bone.
Keel on sternum (chest bone extension)
Provides surface for flight muscle attachment.
Crop (storage chamber in esophagus)
Stores food temporarily.
Gizzard (muscular stomach part)
Crushes and grinds food.
Four-chambered heart
2 atria + 2 ventricles → Complete separation of oxygenated and deoxygenated blood.
Advanced nervous system
Sharp vision and hearing.
Syrinx (voice box)
Located at lower end of trachea.
Air sacs connected to lungs and bones
Allow continuous airflow, improve oxygen supply, and reduce body weight.
Lungs have parabronchi (tiny air tubes)
Provide efficient gas exchange.
Amniotic eggs
With yolk, albumin, and shell → prevent desiccation and provide nutrients.
Internal fertilization, external development
Birds are oviparous (egg-laying).
✈️ Examples:
Flightless Birds (Running birds):
Ostrich, Kiwi, Rhea, Cassowary, Emu
Flying Birds:
Pigeon, Parrot, Crow, Eagle, Robin

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