some birds can fly but others can't which are the adaptation of flying birds
Answers
we can see penguin which is a bird but adapted it's wing for swimming
Answer: Yes, it's evolution of birds.
Explanation: Just like us, human beings, we adapted to live in stone age, as the evolution happened rapidly until modern age, we have been adapting to our surroundings.
Even in ancient time, it is said birds used to be big but as the evolution happened, they also started to adapted to their surroundings just like us. Some birds started to live on land and lost their ability to fly in the sky, some started to search for food in water, they evolved their feathers to be waterproof and others too adapted to their surroundings and lived in their respectable in habitats. It's just the adaption ability of the birds so that they can survive in various situations~