Volant adaptations

  • Animal inhabiting the aerial environment show many Volant (flying) adaptation for the aerial mode of existence.
  • These animals are known as volant forms.
  • Fishes, amphibians, reptiles, birds and mammals among vertebrates, and insects among invertebrates exhibit volant adaptations.
  • Flight is of two types: i) active or true flight b) passive flight or gliding.

A)Active or true flight

  • It involves long and sustained flight through the air.
  • It implies power. The true fliers move the wings with varying degrees of rapidity.
  • True flight is seen in birds, bats and insects.

 

i)Body contour

  • The birds possess boat shaped or spindle shaped (streamlined) body without any protruberances.
  • Thus, they offer the least amount of resistance for movement in air.

ii)Wings

  • The forelimbs are modified into wings in birds.
  • In bat the wings are made up of folds of skin, which are known as patagium.
  • The upward and downward strokes of the wings help in the elevation of the bird and its subsequent propulsion.
  • Changing in direction during flight is caused by tail feathers.
  • The different parts of wing work as a single unit.
  • A row of quill feathers called remiges is present on the posterior ridge of the wing.

iii)Feathers

  • The body of bird is covered with feathers, which are beneficial to the birds in many ways.
  • They act as blanket to insulate the body from external environment. Thus, they maintain high body temperature which is essential for high metabolic rate during flight.
  • They form a smooth and closely fitting covering which reduces friction.
  • It also makes the body light.

iv)Reduction in body weight

  • The bones are hollow and air filled i.e. pneumatic type.
  • The large pneumatic bones of the skeleton are responsible for reducing the body weight.
  • It also offers large surface of attachment for muscles.

Image result for flight muscles of birds                Image result for flight muscles of birds

v)Flight muscles

  • Birds possess three types of light muscles.
  • Pectoralis major, pectoralis minor and coracobrachialis are the types of muscles.
  • Pectoralis major and coraco-brachialis by their contraction serve to pull the wings downwards while the pectoralis minor serves to pull the wings upwards.

vi)Presence of neck and beak

  • The neck is highly mobile and mouth is produced into beak in birds.
  • The highly mobile neck is used in feeding, nesting, offence and defense.
  • Beak helps in picking up grains like forceps.
  • It also helps in tearing and cutting.

सम्बन्धित छवि                         Image result for perching birds

vii)Bipedal locomotion

  • The hind limbs are adapted for walking.
  • They are strong and shifted anteriorly to support the body weight and show bipedal locomotion.
  • The hind limbs bear 4- clawed digits three in front and one behind.

viii)Energy for flight

  • Blood is oxygenated twice during respiration due to which a high rate of metabolism occurs.
  • Thus, birds are provided with larger amount of energy which is essential for long and sustained flight.

ix)Perching mechanism

  • The hind limbs are well suited for perching mechanism in birds.
  • When a bird lands on a perch, the bending of legs exerts a pull on the flexor tendons which make the toes flex automatically and to grip the perch.
  • The perching is so efficient that the birds can sleep while sitting on trees without any fear of falling.

birds adaptations for flightको लागि तस्बिर परिणाम                 birds adaptations for flightको लागि तस्बिर परिणाम

x)Broad sternum

  • The sternum is broad, usually with a longitudinal ventral keel for the attachment of flight muscles.

xi)Air sacs

  • Birds bear additional respiratory air sacs which supply more oxygen for rapid oxidation during flight.
  • They also provide buoyancy during flight.

xii)Short tail

  • The tail of a bird is short and bears a series of long feathers which can be spread in a fan like manner.
  • It serves as a rudder in steering and balancing organ in perching.

xiii)Sense organs

  • In birds, the brain has enlarged optic lobes, which perform sharp vision.

Image result for sense organs of birds                                    Image result for sense organs of birds

B)Passive or gliding flight

  • Animals cannot fly for long time in this type.
  • The animals simply take an initial leap or jump from a high point to lower level and just glide in air with the help of certain organs.
  • It may sometimes cover a horizontal distance of many meters.
  • There is no involvement of locomotive force other than gravity.
  • Here, the wings are made of patagia which cannot move up and down by muscular action.
  • This type of flight is performed by a number of arboreal animals like the flying fish (Exocoetus), flying frog (Rhacophorus), flying dragon(Draco volans), birds (Ostrich), mammals such as flying phalangers (Petaurus sciureus), flying squirrel, flying lemur, etc.
  • They show following adaptation for the gliding flight.

i)Enlarged pectoral fins

  • Flying fishes possess very large and highly developed pectoral fins.
  • They are used as parachutes to make along glide in air above the water surface.
  • The lower large lobe of caudal fin helps in leaping by accelerating speed.

ii)Development of patagia

  • Patagium is fold of skin present between forelimbs and hind-limbs.
  • In flying lizards (dragon), the patagium extends on either side of the trunk and is supported by 5 to 7 pairs of long ribs.
  • Flying gecko (Ptychozoon) is another flying lizard in which lateral expansion of patagium extends along the side of the neck, body, tail, limbs and between toes.
  • Flying snakes leap by the concave ventral side of body.

rhacophorusको लागि तस्बिर परिणाम                        draco volansको लागि तस्बिर परिणाम

iii)Webbed feet

  • In flying frog, the webbed feet helps in long leaps among the trees.
  • The webbed feet serve to increase the area of the supporting column of air.
  • It also partly checks the speed before landing and further reduces the impact.
  • The digits terminate in adhesive pads which help in sticking to smooth surfaces.

Volant adaptations

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