feathers are a part of some wings & wings are used to fly through air by birds ->  wings and feathers are used to fly by birds  wings and feathers are used to fly by birds & if something is used by an organism for a process, then that something has a positive impact on that organism's ability to perform that process ->  wing and feathers have a positive impact on a bird's ability to fly  hollow bones cause an animal to be lightweight & being lightweight has a positive impact on an animal's ability to fly ->  hollow bones have a positive impact on an animal's ability to fly  wing and feathers have a positive impact on a bird's ability to fly & hollow bones have a positive impact on an animal's ability to fly ->  wings and feathers and hollow bones have a positive impact on a bird's ability to fly  avoiding predators has a positive impact on an animal's survival & some birds use flight to avoid predators ->  some birds use flight for survival by avoiding predators  avoiding predators has a positive impact on an animal's survival0 & animals require food for survival ->  some birds use flight for survival by finding food  some birds use flight for survival by avoiding predators & some birds use flight for survival by finding food ->  many birds use flight for survival  wings and feathers and hollow bones have a positive impact on a bird's ability to fly & many birds use flight for survival ->  birds use wings and feathers and hollow bones for survival by positivly impacting their ability to fly  birds use wings and feathers and hollow bones for survival by positivly impacting their ability to fly & adaptations are used for survival -> an example of an adaptation for flight in birds is feathers / wings / hollow bones