Aves: Definition, Characteristics, Classifications, Examples, Types, Facts

Class Aves, commonly known as birds, includes warm-blooded, feathered vertebrates with a unique ability to fly, though some are flightless. Birds are characterized by their beaks, lightweight skeletal structure, and specialized respiratory system. They reproduce by laying eggs and exhibit high parental care. In this article, the classification of aves, characteristics, evolutionary history, morphology and anatomy, feeding, and adaptations are discussed. Class Aves is a topic of the chapter Animal Kingdom in Biology.

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This Story also Contains

1. What are Aves?
2. Taxonomy and Classification of Aves
3. Characteristics of Aves
4. Aves Examples
5. Morphology and Anatomy of Aves
6. Feeding and Digestion in Aves
7. Adaptations for Flight in Aves
8. Behaviour and Communication in Aves

What are Aves?

Aves, also known as birds, are a class of endothermic vertebrates whose features include feathers, beaks that do not have teeth and high metabolism. Aves are categorised mainly by the mode of locomotion, namely, by flying; but some of them do not possess this faculty. It is important to study birds in biology because they are invariably involved in important processes in ecosystems, for example as pollinators, seed replanters and controllers of pests. Moreover, birds are conscious signs of the state of the environment and the level of biodiversity. Due to their wide variation in terms of adaptations and behavioural characteristics, they provide relevant information on evolution, thus making them an important study for ecological and evolvement processes.

Taxonomy and Classification of Aves

Systematics of taxonomic grouping is a way of categorising living organisms in the form of a nested hierarchy based on taxonomy and phylogeny. The major levels of classification aves are:

Kingdom:

The level that can be considered to be on the top of the hierarchical structure comprises the greatest number of elements. Gentile birds are mentioned as part of the kingdom Animalia, which consists of all multicellular eukaryotes.

Phylum:

A rank subordinate to the kingdom, in which organisms are classified according to the general body designs and structural characteristics. Birds belong to the Phylum Chordata these are animals having characteristics like a notochord at some point in their development, a hollow nerve cord and pharyngeal slits.

Class:

A more specific rank within a phylum rank. Birds fall under the Class Aves; therefore, they differ from mammals in the Class Mammalia as well as reptiles in Class Reptilia.

Also Read-

• MCQ on Aves
• Animal Kingdom
• Phylum Platyhelminthes
• Phylum Ctenophora

Characteristics of Aves

The general characteristics of Aves are discussed below-

Feathers: The structure and purpose of a long hind toe and a short, curved tail, the behaviour of walking, running and flying, and the mechanisms which make flight possible are all in some way special to birds.

Beaks: Birds have a mouth structure that does not have teeth but have beaks or bills depending on their diet and their favourable habitats.

High Metabolic Rate: Birds are endowed with high metabolic rates to meet flights’ energy requirements as reflected by respiratory and circulatory systems.

Hollow Bones: Some of the adaptations include; in the case of bones, many birds have lightweight hollow bones, which help to decrease body mass while at the same time providing the necessary support for flying.

Reproduction: Birds provide for their young hard-shelled eggs and most species of birds display special care-giving patterns.

Endothermy: Avians are all warm-blooded organisms, implying that they continuously regulate their body temperature irrespective of the prevailing climatic conditions.

Evolutionary History Of Birds

Key points in the evolutionary history of birds include:

Feather Evolution: Brightly coloured feathers were first developed for protection and showiness which then helped in flying.

Flight: The development of flight raised new kinds of opportunities and thus the birdline is more diverse.

Adaptive Radiation: Thus, following the Cretaceous-Paleogene extinction event that propagated the non-avian dinosaurs the birds went through a process called adaptive radiation to achieve their current state.

Aves Examples

Some examples of birds belonging to Class Aves:

1. Passer domesticus – House Sparrow
2. Corvus splendens – Indian Crow
3. Columba livia – Rock Pigeon
4. Psittacula krameri – Rose-ringed Parakeet
5. Struthio camelus – Ostrich (flightless bird)
6. Pavo cristatus – Indian Peafowl
7. Haliaeetus leucocephalus – Bald Eagle
8. Falco peregrinus – Peregrine Falcon
9. Apteryx – Kiwi (flightless bird)
10. Aquila chrysaetos – Golden Eagle

Morphology and Anatomy of Aves

The external morphology and anatomy are listed below:

Feathers:

Types: Body feathers of birds are of different types such as contour feathers which give the shape of the bird’s body, down feathers which maintain the temperature of the bird’s body and flight feathers which help birds to fly.

Structure: A feather is a structure of keratin that has a central spine called a rachis with branches known as barbs and hooks known as barbules that attach to form a light structure.

Beak:

Adaptations: A bird’s beak is closely associated with its diet and very unique in its design depending on the size of the bird.

For instance: Raptors that feed on flesh have hooked beaks while Hummingbirds that feed on nectar have long slender beaks.

Wings:

Flight Adaptations: It is a change in limb that has the structure of the forelimb but differs in size and shape with the mode of flight. Some birds like albatrosses have long and narrow wings that are suitable for gliding across and some birds have short and wide-spread wings suitable for manoeuvring like hawks.

Structure: Wings include a humerus, a radius, an ulna, and a modified carpal that supports the primary remiges.

Feet:

Adaptations: The feet of birds depend on the place they live, their kind and the activities they engage in. Flying birds’ feet are positioned three to four feet forward while wading birds have an adaptation of webbed feet, valued for swimming.

The internal morphology and anatomy are listed below:

Aves Skeletal System

• Lightweight Bones: Feathers on the body of birds are also relatively light since they squeeze conveniently inside the bird casings mainly because of the lightweight, hollow bones which also help decrease the weight in the body and fly. The bones have built-in stiffeners for strength Besides, the bones have integrated gussets for strength.

• Fused Bones: Some of the birds’ bones are fused developing more sturdy structures like the furcula commonly known as the wishbone and synsacrum that offer support in flight.

• Keel: The main elements of the birds are also well-developed and include a large sternum or breastbone upon which huge flight muscles are attached.

Aves Respiratory System:

• Air Sacs: Birds also have a different respiratory structure, now with air cavities that continuously pass air through the lungs. This system allows optimal gas exchange so suitable for the bird’s metabolism especially when flying.

• Lungs: The lungs are small and highly specialized for respiration; para bronchi which are the airways are unidirectional providing an efficient way of getting high O2 uptake.

Aves Digestive System:

• Crop: A storage pocket in the oesophagus where food is moistened before being passed to the stomach preparatory for digestion.

• Stomach: Birds have a divided stomach and the hormones controlling digestive juices are secreted in the pro-ventriculus while the gizzard grinds the food often with the help of stones swallowed intentionally.

• Intestine and Cloaca: The nutrition is obtained by the intestine while the cloaca is a container for digestion, urination, and copulation organs.

Aves Circulatory System:

• Four-Chambered Heart: Birds have four-chambered hearts that separate oxygenated and deoxygenated blood as efficiently as mammals do.

• High Metabolic Rate: Due to high metabolism, birds are characterized by a developed and highly effective circulatory system for oxygen and nutrient supply.

Diagram showing the Internal Features of a Bird

Feeding and Digestion in Aves

The feeding process is described below-

Adaptations of Beak and Digestive Tract for Different Diets

Birds have evolved diverse beak shapes and digestive tract adaptations to suit their diets:

Beaks:

• Carnivorous Birds: Long, hooked beaks (i.e., eagles) for tearing the flesh into pieces.

• Granivorous Birds: Special and robust, pointed-shaped (e.g., finches) for purposes of crushing seeds.

• Nectarivorous Birds: Short, sharp and straight beaks.g.g., Nightingales), Long slender curved beaks (e.g., Hummingbirds) for nectar.

• Piscivorous Birds: Long sharp pointed beaks for fishing for example in herons.

Digestive Tract:

• Birds also have specific digestive tracts for the different foods that they eat.

• Herbivorous Birds: Increased length of the small intestines for breaking down plant material high in fibre.

• Insectivorous Birds: The intestines of these animals needed less length and time to digest food particularly insects rich in protein.

Role of Gizzard in Digestion

• A gizzard is a muscular part of the stomach; that grinds food, usually with the aid of stones swallowed with the food (gastroliths).

• Console for the birds that feed on hard capsules like the seeds because it helps to grind the food before swallowing.

Adaptations for Flight in Aves

The adaptations in Aves for flying are given below:

Aerodynamics of Bird Flight

• Lift and Thrust: Birds lift an amount of weight that is through the flapping of their wings causing pressure changes. Downstroke of the wings creates thrust.

• Wing Shape: Feather wings have a curved shape on top and a relatively flat surface at the bottom (airfoil shape) and operate on the Bernoulli principle that says the pressure at the top has to be less than that below it if the speed of the air moving over it is greater than that under the wing.

Wing Structure and Function

Feathers:

• Primary Feathers help propel it forward, these feathers are found at the end of the wings.

• Secondary Feathers are located closer to the body and they deliver lift.

Wing Types:

Soaring Wings are long and narrow for gliding for example albatross.

Flapping Wings are smaller and less massive for convenience (e.g., sparrows).

Bones:

Thin and empty to decrease mass or weight and maintain the strength of the member at the same time. Such important bones integrate the humerus, radius, ulna, and fused hand bones hosting flight feathers.

Muscles Involved in Flight

• Pectoralis Major: The major thoracic muscle involved in the production of the powerful downstroke that’s employed in generating the thrust.

• Supracoracoideus: A much lesser-sized muscle located directly beneath the pectoralis major which is in charge of the wing-beating or rather the wing-up stroke.

• Arrangement: All these muscles are attached to the keel of the sternum large central bone and large tough breast bone that offer support for strong flight.

Behaviour and Communication in Aves

The behaviour and communication are listed below-

Social behaviour

Flocking: Offers protection against predators increases the rate of food finding and allows the young to learn how to find food.

Territoriality: Resource-defense polygyny is a common practice among birds because birds always fight for a place where they can get food, build their nests, and mate.

Vocalisations

Types: Sirens (structure more complex and with a higher pitch to advertise or advertise territory) and calls (shorter sounds to sound the alarm, move synchronously, and remain in touch).

Purposes: Greetings, courtship, the assertion of dominance, and announcement of presence to rivals and warning of the presence of foes.

Bird Intelligence and Problem-Solving Abilities

Intelligence: Corvids and parrots are major groups of birds that depict high intelligence.

Problem-Solving: In problem-solving, utilize objects as well as demonstrate problem-solving behaviours consistent with planning and learning from prior results.

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