Re-write the paragraph while fixing the sentence fragments. Re-wording might also be necessary.
I often wonder. While looking out my window. How far do birds travel to land here? And sit in the tree by my house. And then, I think about the power it takes to fly an airplane. And see how small the birds are. They must be very well adapted to survive their yearly migrations. As they travel north and south with the changing seasons. If I was a bird. I might choose to stay in warmer climates all year. Instead of flying north. Where it is colder. That is definitely what I would do. If given a choice. I can only imagine the adventures my flying friends have experienced. Traveling much further than I have. Maybe than I ever will. Must finish my physics homework. So I can someday to learn fly. An airplane to these far off places.