Question

Birds can fly because of
A) Feathers
B) Wing
C) Hollow bones
D) All of the above

Answer 1

Hint:- Birds belong to the class Aves. They are believed to have evolved from feathered dinosaurs called theropods (belonging to the reptilian category). All birds have features such as feathers, wings, and beaks with no teeth. They are warm-blooded, oviparous (egg-laying) vertebrates. Just like the human heart, a bird's heart is also four-chambered.

Complete answer:
Feathers are one of the most defining features of the birds. It is an epidermal layer of growth composed of beta-keratin protein. It is the flight feathers that aid in flying. The flight feathers are found in the wings and tail of the bird. The feathers on the wings are called remiges and these feathers have been classified into various types based on their position on the wings. All the feathers on the wing (remiges) work in tandem to provide the lift and the thrust required to make a flight possible.
Forelimbs found in terrestrial vertebrates have been modified to wings in the case of birds. The shape of the wings differs depending on whether the bird requires a speedy flight or one that saves more energy. Aspect ratio and wing loading are the two factors that determine the shape of the wings. Based on the wing shape wings are classified into- high-speed wings, high aspect ratio wings, elliptical wings, and soaring wings with deep slots.
The skeletal structure of the birds is quite light. Hollow bones are a modification observed in bird skeletal systems. Air sacs are present in these hollow bones. These sacs get filled with air and help the bird breathe. It is like an extension of the lungs. Even while flying, the bird is not deprived of oxygen and has enough energy to make a flight.
So, the correct answer is option (D).

Note:- Birds such as Ostrich, Kiwi, Emu, etc. do not fly despite having two wings. Two major morphological changes can be attributed to these flightless birds. One of the reasons is that these birds have really small wings or at least small in comparison to their body weight. Birds have this breastbone extension called keel that supports the wing muscles and aid in flight. This is either missing or greatly reduced in flightless birds.