Class Aves

🕊️ Class Aves (Birds)

Aves are warm-blooded vertebrates characterized by the presence of feathers, wings, and hard-shelled eggs.

🪶 General Characteristics

• Feathers cover the body, forming flight surfaces that provide lift and aid in steering.

  • They also help prevent heat and water loss.

• Birds are endothermic (warm-blooded) — they obtain heat from cellular respiration.

• Because they maintain a constant internal temperature, birds are also homeothermic.

🦴 Body Structure

• The body is streamlined and spindle-shaped to reduce air resistance during flight.

• Forelimbs are modified into wings.

• Bones are light due to air spaces (pneumatic bones).

• Bill (beak) replaces teeth and is covered by a light sheath.

• The sternum (breastbone) has a keel, a large bony ridge for attachment of flight muscles.

• Birds possess a crop, a storage pouch in the esophagus that allows quick ingestion of food.

• The gizzard, a muscular part of the stomach, crushes and grinds food.

• The heart is four-chambered, ensuring complete separation of oxygenated and deoxygenated blood.

🧠 Nervous and Sensory System

• Birds have a highly developed brain and nervous system.

• Vision and hearing are well developed and essential for flight and navigation.

🫁 Respiratory System

• The nasal passages open into the pharynx, which leads to the trachea, then bronchi.

• The syrinx, located at the lower end of the trachea, is the organ of voice.

• Bronchi lead to a system of air sacs that occupy much of the body and extend into some bones.

• Air sacs connect to the lungs, which consist of parabronchi — small air tubes allowing continuous airflow for efficient respiration.

🥚 Reproduction

• Birds lay amniotic eggs with a large amount of yolk and albumin, enclosed in a hard or leathery shell.

• Fertilization is internal, but development occurs externally, so they are oviparous.

🕊️ Classification by Flight Ability

• Flightless (Running) Birds: Ostrich, Kiwi, Rhea, Cassowary, Emu.

• Flying Birds: Pigeon, Parrot, Crow, Eagle, Robin, etc.