Question

Flightless birds lack
(a) Wings
(b) Keel in Sternum
(c) Both a and b
(d) Feathers

Answer 1

Hint: Flightless birds are the birds that through evolution lost their ability to fly along with flight muscles as they adapted to the new environment. They are commonly called as ratites. Penguin, Kiwi, emu are some common examples of flightless birds.

Complete Step by Step Answer:
- Flight is the most common type of locomotion in the birds in the natural world. the energy expenditure required for the flight increases proportionally with the body size
- Keel, the projection of bone from the sternum( breastbone) of a bird to which the powerful flight muscles are attached.
- Keel anchor the strong pectoral muscles required for flight
- Flightless birds have a bulky body, long strong legs, small Wings bones, and lack keel. By reducing large pectoral muscles, flightless birds conserve their energy by decreasing their basal metabolic rate.
- Due to the absence of keel in flightless birds their muscles are not suitable for flight.
- Penguins, on the other hand, have retained the keel, but it has evolved to accommodate the bird's flightless aquatic existence.
So, the correct answer is, ”Keel in Sternum”.

Additional information:
- In flightless birds, the bird’s physical size and leg bone and toe structure are interrelated characteristics. Their body consists of hollow bone thus having a light skeleton that helps them in flying. They also have a large body supported by heavy backbones and thick strong feet adapted for running.
- Inaccessible Island rail is known to be the world’s smallest flightless bird.
- On the other hand, Ostrich is the largest flightless bird.
- There are lots of families of these birds which have been extinct.
- One of the Known species - gigantic herbivorous moa(New Zealand) , in which wings completely disappeared.

Note: For any bird to fly, the wings muscles must be anchored to its keel as they serve as powered springs connected to wings bone that in turn levered to thoracic bones for the flutter. The wishbone or furcula is responsible for the strengthening of the thoracic cavity in the case of birds.