At first glance, bird feathers seem to have a very simple structure. When we study them closer, however, we come across the very complex structure of feathers that are light yet extremely strong and waterproof.
Birds should be as light as possible in order to fly easily. The feathers are made up of keratin proteins keeping with this need. On both sides of the stem of a feather are veins and on each vein are around 400 tiny barbs. On these 400 barbs are a total of tinier 800 barbs, two on each. Of the 800 tinier barbs which are crowded on a small bird feather, those located towards the front part have another 20 barbs on each of them.
These barbs fasten two feathers to one another just like two pieces of cloth tacked up on each other. In a single feather are approximately 300 million tiny barbs. The total number of barbs in all the feathers of a bird is around 700 billion.
There is a very significant reason for the bird feather being firmly interlocked with each other with barbs and clasps. The feathers should hold tightly on the bird so as not to fall out in any movement whatsoever. With the mechanism made up of barbs and clasps, the feathers hold so tightly on the bird that neither strong wind, nor rain, nor snow cause them to fall out.
Furthermore, the feathers in the abdomen of the bird are not the same as the feathers in its wings and tail. The tail is made up of relatively big feathers to function as rudder and brakes; wing feathers are designed so as to expand the area surface during the bird's wing beating and thus increase the lifting force.
...Allah did not create the heavens and the earth and everything between them except with truth and for a fixed term...(Surat ar-Rum, 8)