Is it not related to the fitness of birds to the terrestrial-air habitat?

Many birds are adapted to flight. In the course of evolution, various parts of the thal have evolved or changed. This was necessary to obtain some advantages during the flight. For example – pectoral muscles developed in birds. Also, birds have a special body shape that is most optimal for “cutting through” the air. But some features are not related to flight. For example – the shape of the beak. In theory, the shape of the beak affects flight, but in practice, different birds have their own characteristics, which are primarily associated with the way they get food, and not with flight.