Aves are a class of endothermic vertebrates, commonly known as birds. These animals fall under the phylum Chordata carrying specific features such as toothless jaws with beak, laying of eggs with a hard shell, etc.
Estimated 9000 species of Aves are present in the terrestrial animal kingdom. The capability of flying is the most dominant feature of this species. Their lightweight skeleton structure with strong but hollow bones helps them to fly.
Along with these salient features of Aves, the most visually attractive and remarkable characteristic is their colourful feather. A wide range of feathers with its unique pattern can be seen in the class of animals.
Aves are also called social animals as they can build nests, show territorial behaviour, and engage in courtship.
Example
Some of the Aves examples are Pigeon, Parrot, Sparrow, Owls, Penguins, Hummingbird, Crow, etc.
Aves Characteristics
Some general characteristics of Aves are the following-
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One of the most visible class Aves characteristics is they are bipedal feathered animals. The fore-limbs of birds have developed into wings that help them to fly.
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Their back-limbs have become legs that help them for swimming, walking, etc. Mostly, birds have four toes on their legs. However, two or three toes are also rarely visible.
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Aves are homeothermic or warm-blooded creatures. Because of this, birds can keep a stable body temperature even when flying at high altitudes.
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Birds don’t have any skin glands other than the uropygial gland or oil gland. This gland is situated near the tail.
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Their jaws are transformed into beaks and they don’t have any teeth. With the help of a beak, birds can feed in different ways like tearing flesh, crushing seeds, sipping nectar, etc.
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Additional chambers called gizzard and crop are found in their alimentary canal. The crop chamber helps to soften the stored food, whereas the gizzard crushes the food. Few seed-eating birds like pigeons lack gall bladder in their system.
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Lungs act as the primary respiratory organ in birds. Their lungs are inelastic and spongy. Lungs have air sacs to supplement respiration.
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In birds, an organ called syrinx helps to produce voice.
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Birds have a four-chambered heart and a reduced renal portal system. Also, their cardio-vascular system lacks sinus venosus.
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The kidneys in birds are metanephric that help to filter the nitrogenous fluid waste via the ureters, into the cloaca. Their renal system lacks a urinary bladder.
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Aves have a more developed brain then reptiles. Their brain consists of the cerebrum, cerebellum, and large optic lobes. Furthermore, 24 cranial nerves are present in their nervous system.
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Birds have highly developed sight, but their smelling sense is poor. They have eyes and visible ear openings. Their ears are divided into three parts – internal, middle, and external.
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Their endoskeleton is bony, and the bones are hollow. For this reason, the bones in birds are lighter than most animals. The bones lack bone marrow. The skull consists of a single occipital condyle.
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The female birds have one ovary on the left side of the body and one oviduct. However, non-functional right ovaries and oviducts can be found in some cases.
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Sexual dimorphism can be found in Aves, and they are oviparous. Bird eggs consist of four embryonic membranes – yolk, allantois, amnion, chorion.
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Some other class Aves facts – they are spindle-shaped, and their shape helps to reduce the wind resistance while flying. Also, their feather passes the air to minimise air friction.
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The fight muscles of Aves are highly developed.
Classification of Aves
Aves can be categorised into two classes. Here is the Aves classification up to order-
This class of Aves is extinct. Their beaked jaws had teeth and the tail was long like a lizard.
Example – Archaeopteryx
This class of Aves is both extant and extinct. They have toothless beaked-jaws and a short tail.
Example: Duck, Penguin, etc.
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Characteristics of Aves – At A Glance
The common characteristics of all members of Class Aves are warm-blood, forelimbs modified into wings, well-developed flight muscles that help during the flight, their hind limbs are adapted for walking, hopping, perching, grasping, wading and swimming, epidermal scales on their legs, endoskeleton is bony with long hollow bones filled with air cavities (known as pneumatic bones), spindle-shaped body minimizes resistance of the wind, feathers help in preventing heat loss and reduce air friction by providing passage to the air, have no skin gland except the oil gland, lower and upper jaws are modified into a beak, have no teeth and sharp eyesight, the alimentary canal has a crop and a gizzard, pigeons and other seed-eating birds lack gall bladder, have spongy and elastic lungs for respiration, a special vocal organ called syrinx is present at the base of trachea, the heart is four-chambered, RBCs are oval, nucleated and biconvex, 12 pairs of cranial nerves are present, have a single ovary and oviduct on the left side, are oviparous and exhibit sexual dimorphism.