How I think birds fly

I think birds fly by powerful muscles and very light bones.I don't think that birds run off then fly.The bones in the wings of birds are hollow, this means the wings are empty.Some birds have really long big feathery wings.Other birds have really short little wings.Do they use their wings in the same way?I think they don't use it in the same way because the birds with big wings will go faster and birds with small wings abit slower Alysha.