Flight

Flight is one of the most involved adaptations an organism can have. What that means is that when an organism is on the evolutionary path to flight, everything else about that organism's morphology/lifestyle must change to accommodate the ability to fly. The bones must become lightweight, and habitat is most likely at a high altitude. Organisms evolving for flight have to make themselves as light as possible, meaning that heavy feathers are not a good option. The body must become streamlined in order to get the best possible flying efficiency, or face losing energy to fight additional air resistance from a non-aerodynamic body. Flying has only evolved once in mammals: the bat. The bat has a lightweight skeleton with long, thin arms that provide the framework for their wingspan. Unlike most flying animals, their eyesight can actually be very poor, and some species of bats rely on echolocation to fly around and locate prey. Flying is an all-in, evolutionary commitment, and a lifestyle that has been lived out successfully by many thousands of animals.