Aerial Mammals
• 3-possible modes of aerial locomotion or flight-gliding, soaring & flapping • Gliding is rudimentary flight displayed by certain fishes (Exocoetus), amphibians (Rhacophorus), lizards (Draco) & among mammals by some phalangers (flying lemurs & squirrels)
Exocoetus
Rhacophorus
Draco
Flying lemurs
Flying squirrel
• Soaring & flapping are more efficient & need more profound morphological & physiological adaptations • Soaring flight is attained by certain birds • Flapping flight is attained by both birds & bats
I. Gliding Mammals & Adaptations
1. Gliding Mammals
Order Marsupialia •Flying phalangers or possums (Petaurus) & feather tails (Acrobates)
Possums
Acrobates
Order Rodentia • Kashmir woolly flying squirrel (Eupetaurus cinereus) & brown flying squirrel (Petaurista phillipensis)
Eupetaurus cinereus
Petaurista phillipensis
2. Gliding Adaptations • Body is elongated, flattened & streamlined • Limbs long & equal • Tail long & gradually tapering • Double fold of furred skin (patagium or parachute membrane) stretched on either side between neck, limbs, body & tail
• It is sometimes reinforced with a cartilaginous rod springing from the elbow or wrist • When the animal is at rest, parachute is scarcely visible as it remains tucked or close to the body by its own elasticity
3. Nature of Gliding Flight • Gliding is not a true continuous flight but merely a prolonged aerial leap, covering 10-20 meters at the most • Gliding mammal glides from one tree to another, smoothly & swiftly downwards supported by the outstretched parachute & limbs
• Aerial progress is in straight line rapidly losing height & with little maneuverability • However flight can be guided to some degree by changing flight position of limbs by twisting parachute membrane & tail • Before alighting, animal raises front body part to check speed & to soften its impact on landing target
II. Flapping or Flying Mammals & Adaptations
1. Bats • Order Chiroptera • Only mammals with true & sustained flight effected by the flapping or up & down strokes of wings • Built for flight & compete very well with birds
2. Flight Adaptations of Bats • Adaptations are infinitely more pronounced • Modifications are not so conspicuous in their external features • However, radical changes have occurred internally in their skeleton & musculature
a. Wings • Patagia of bats are paper-thin, elastic membranes which are extensions of leathery skin from lateral sides of body, legs & tail • Forearm is greatly elongated carrying a hand with 5-fingers
• In small insectivorous Microchiroptera first finger or pollex is short , free & sharply clawed • Other 4-fingers are clawless, enormously lengthened & embedded in the wing web to support it
• Like ribs of an umbrella they close & open the wing & keep it taut when expanded • In large fruit eating bats (Megachiroptera) the 2nd finger also ends in a claw • 3rd finger is largest corresponding to the leading edge of wing membrane
• In most bats an interfemoral membrane also encloses the tail wholly or partially extends between hindlegs • Also supported by a spur of bone (calcar) projecting from tarsus of each foot • A similar ante-brachium membrane connects neck with humerus bone of upper arm
• Thus, there is a continuous & uninterrupted parachute of skin around bat’s body • Bat’s muscles & other body structures are specially designed to support & operate wings • Bat has a capacious thorax containing a remarkably large heart & lungs
• Keeled sternum offers space for the attachment of great pectoral muscles which sustain arms in flight • Though converted into wings for flight the bat’s arms & hands are also used for walking, climbing, holding, food & killing prey in flight
b. Legs • Hind limbs are small, weak & with sharp curved claws on toes used for suspending bat head down from a tree branch or perch while resting or sleeping
• Knee-joints directed backwards instead forwards • Help in maximum spread of wing membranes but is of little help in other movements
c. Tail
•Variable in size •May be large, small or scarcely visible
• When well developed supports the inter-femoral membrane which can act as a brake to flight • Used as a large pouch for holding prey or food or even as an aerial cradle for reception of a new born baby
d. Teeth • Milk dentition of bats is curious in adaptation to flight • Young are often born with small hook-like or needlelike teeth similar & sometimes forked • Supposed to serve young for gripping firmly maternal teats while mother is flying
e. Senses • Bats are extremely modified for nocturnal flight • Able to fly even in total darkness with ease & swiftness avoiding obstacles
• Possess special sense organs allowing them to perceive prey & surrounding obstacles at a distance in total darkness • Supersenstive to sound & possess a natural echoapparatus or radar system of their own
• In flight bats keep their mouth open & continually emit tremendous bursts of supersonic or ultrasonic sounds quite inaudible to human ear • Warning echoes reflected back enable bats to locate & evade obstacles in their path
• In numerous insectivorous bats sensitive accessory lobes on ears (tragus) help to pick up warning echoes • Besides, certain bats have skin flaps encircling nose (nose-leaf) • Exact use not well understood but probably it acts as an antenna for perception of air vibrations
• Wing-webs are abundantly supplied with scattered nerves & blood vessels & probably act as tactile organs which also help in avoiding obstacles in their course during nocturnal flights
• So incredibly sensitive are bats that thousands of may them swirl around for hours in total darkness in a cave without a single collision • The aerodynamics of bats drive engineers mad & are quite beyond us ordinary mortals
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