Flight or Aerial Adaptation in Birds

The birds have a unique ability to fly and for this, there are various adaptations are acquired. In birds, the most obvious adaptation to flight is the wing, but the flight is so energy-demanding, that’s why birds have evolved many other adaptations to improve the efficiency of their flight.

Types of flight adaptation in birds

There are two main types of flight or aerial adaptation in birds:

  1. Morphological adaptation
  2. Anatomical adaptation
Morphological Adaptation

Most birds show the following important morphological flight adaptations:

Body contour: Bird’s bodies are streamlined, and spindle-shaped to help overcome air resistance.

Compact Body:

  • The body of birds is compact and is light and strong dorsally and heavy ventrally. This shape helps in maintaining equilibrium in the air.
  • The wings’ attachment is high upon the thorax. The light organs like the lung and sac is placed at a high position and the low central position of heavy muscles, sternum and digestive organs are other morphological facts with great significance.

Body covering of Feather:

The body of all birds is covered by special integumentary derivatives called feathers.

 

Advantages of feathers:

  • The smooth, closely fitting, and backwardly directed contour feathers make the body streamlined that helping the birds to pass through the air by reducing the friction to the minimum.
  • The feathers protect from hazards of environmental temperature.
  • The feathery covering makes the body light also.
  • The feathers also work like blankets that envelop air around the body of birds which helps to maintain its buoyancy.
  • The vanes of each feather have hooklets called barbules that zip the vanes of individual feathers together, giving the feathers the strength needed to hold the airfoil (these are often lost in flightless birds)
  • The non-conducting covering of feathers insulates the body perfectly and also prevents loss of heat which enables the bird to endure the intense cold at high altitude and also maintains a constant temperature.
  • The wing feathers form a broad surface for striking the air.

Modification of forelimbs into wings:

The bird’s wings are the key to flight. The wings of birds are unique, powerful, and propelling organs that are modified form of forelimbs. The wings are the sole organs of flight.

  • Wings have a central vane to hit the wind, composed of three limb bones, the humerus, ulna, and radius.
  • The shape of the wing is important in determining the flight capabilities of a bird. Different shapes correspond to different trade-offs between advantages such as speed, low energy use, and maneuverability.
  • Both wings spring from the anterior region of the trunk. During rest, they remain folded against the sides of the body, but at the time of flight, they become expanded.
  • The surface area of wings increased by the development of elongated flight feathers, the remiges.
  • The particular shape of the wings, with a thick strong leading-edge, convex upper surface, and concave lower surface causes a reduction in air pressure above and increase below, with minimum turbulence behind. It helps birds in driving forwards and upwards during flight.

Mobility in the neck and head:

  • In birds, the mouth is drowned out into a horny beak which acts as a pair of forceps in picking up things, nest building, pruning, and in other activities in which forelimbs are normally used.
  • In birds, the neck is long and flexible which helps in the movement head.

Bipedal Locomotion:

  • In birds, the anterior part of the body is concerned with flight, and the posterior part of the body is modified for movement on land.
  • For locomotion on the ground and to support the entire body weight, the hind limbs occupy a somewhat anterior position on the trunk and become stouter in the case of ratites which are running birds.

Perching:

  • For arboreal life, the hind limbs of birds are well specialized.
  • The muscles are developed in such a manner that when a bird sits on a branch of the tree, the toes close around the twig automatically. It happens due to a mechanism known as perching. Birds can sleep in this position without any fear of falling off.

Short tail:

  • The short tail of birds bears a tuft of long tail feathers or rectrices, which spread out in a fan-like manner and serves as a rudder during flight.
  • The short tails also assist in steering, lifting, and counterbalancing during flight and perching.
Flight or Aerial Adaptation in Birds : Streamlined body of bird

Flight or Aerial Adaptation in Birds: Streamlined body of the bird

Anatomical adaptation:

In flying birds following anatomical adaptations are found:

Flight muscles:

  • The actions of wings are controlled by the flight muscles that are well developed, weighing about one-sixth of the entire bird, while the muscles of the back remain reduced.
  • The wings are depressed by large muscles, pectoralis major, and elevated by pectoralis minor.

Lightness and Rigidity of Endoskeleton:

  • In flying birds, the skeletal framework is very stout and is lightly built.
  • Mostly pneumatics bones are found in flying birds which are filled with air sacs and provided with secondary plastering to make them rigid.
  • In the bones of birds, the bone marrow is not found.
  • Due to the fusion of bones, the skeletal framework becomes compact, centralized, and rigid.
Characteristics of the endoskeleton of birds:
  • The skull bones are thin and firmly fused with each other.
  • many unnecessary bones have been lost (such as the bony tail of the early bird Archaeopteryx), along with the toothed jaw of early birds, which has been replaced with a lightweight beak
  • The posterior portion of the skull is spongy.
  • In birds, there is an absence of teeth.
  • All the thoracic vertebrae except the last are fused into a single mass giving rigidity to the dorsal part of the vertebral column.
  • The fusion of vertebrae provides a firm fulcrum for the action of wings in striking air.
  • The neck of birds is highly movable; they can move their neck 180 degrees. It helps in preening feathers in all parts of the body.
  • The shortening of caudal vertebrae and formation of pygostyle has assisted stability in air.
    • Pygostyle: It is a triangular plate formed of the fused caudal vertebrae, typically supporting the tail feathers.
  • The breast bone or sternum is expanded having a median ridge or keel for the attachment of major flight muscles in flying birds.
  • The fusion of the pelvis with synsacrum supports the weight of the body when a bird is walking, and also counteracts the effect of shocks as the bird alights.
  • In birds, the absence of ventral symphysis of ischia and pubis permits laying of large eggs.
  • Tarsometatarsus are formed by the fusion of distal tarsals with the metatarsals.
  • Tibiotarsus are formed due to the fusion of proximal tarsals with the lower end of the tibia, which helps to strengthen the legs of bipedal gait.
  • The skeleton of the forelimbs is completely modified for the attachment of feathers and flight muscles. Only three digits are found which are more or less fused.

 

Digestive system:

  • The rectum of birds becomes much reduced in length and never stores the undigested food.
  • There is the absence of a gall bladder in birds which minimizes the body weight to some extent.

Respiratory system:

In birds the lungs are supplemented by a remarkable system of air sacs, these reduce the specific gravity of birds and also facilitate complete aeration of the lungs.

Circulatory system:

The heart in birds is large-sized, four-chambered, powerful, and efficient. In birds, the red blood cells contain a large amount of hemoglobin.

Warm bloodedness:

In birds, the body temperature is high and constant, which enables the bird to take flight at high altitudes and also facilitates activeness in every season.

Excretory system:

  • The urinary bladder is absent in birds. The semi-solid urine is immediately excreted out, as it is not retained for a long time in the body.
  • The metabolic nitrogenous wastes are converted into less toxic and insoluble organic compounds such as uric acid and urates.

Reproductive organs:

In female birds, there is single functional ovary is found on the left side. It also leads to the reduction of body weight which is essential for flight.

 

Reference: https://en.wikipedia.org/wiki/Bird_flight#Flight

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