A specialist in the study of flying bats, the various species, and their activities: Chiroptologists have learned, among other things, that bats are mammals whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight while other mammals are said to "fly"; such as, flying squirrels, gliding possums, and colugos (tree mammals having a fold of skin on each side from neck to tail) all glide rather than fly, and can only maneuver in the air for short distances.