I’m so glad you asked, dear, dear, darkowlblues7. I will be delighted to explain it to you in excruciating detail.
Birds, as you might be aware, are descended from dinosaurs. By this, I am of course referring to the saurischians that were illegally genetically manipulated by their ornithischian overlords. Of course, many prehistory textbooks dispute the reasons behind the experiments, but I’m sure we can all agree the most logical assumption to be made is that the war with the rebel pterosaurs corps was taking a serious toll on the population, and the ornithischians were looking for a secret weapon. They could hardly have known that trying to create a self-combusting Argentinosaurus would result in the destruction of the world as they knew it, ironically leaving only their most controversial specimens to survive!
In short, darkowlblues7, it is science that makes birds fly. Dinosaur science.