Bats are the only mammals capable of true and sustained flight. This often leads to the mistaken belief that their wings are covered in feathers like a bird’s. Bats do not possess feathers on their wings or bodies. Their wings are a remarkable evolutionary adaptation, constructed from skin and bone, not the keratin-based structure of feathers.
Are Bats Mammals or Birds?
Bats belong to the class Mammalia, placing them with humans, dogs, and whales, not with birds in the class Aves. Their bodies are covered in fur or hair, a defining characteristic of mammals. The order for bats is Chiroptera, meaning “hand-wing,” which reflects their unique anatomical structure.
Unlike birds, bats give birth to live young and produce milk to nourish their offspring. Their bones are dense, similar to other non-flying mammals. Birds, in contrast, have specialized, air-filled bones for reduced weight and greater efficiency.
The Structure of a Bat Wing
The bat wing is a highly specialized forelimb, essentially a modified hand that uses a thin, double membrane of skin for flight. This membrane is called the patagium, and it is stretched across dramatically elongated finger bones. The wing skeleton includes a short arm and forearm, but the long bones of four fingers (digits two through five) form the primary support structure.
The patagium is a living tissue composed of external epidermis and an inner dermal layer. It is rich with tiny muscles that actively control the wing’s curvature during flight, a feature not found in feathered wings. Blood vessels run throughout the membrane, and the skin contains minute sensory hairs that help the bat detect changes in airflow.
How Bat Flight Differs from Birds
The flexible, skin-based wing allows bats to achieve a level of maneuverability unmatched by the average bird. Birds rely on layered feathers to create a semi-rigid wing with a relatively fixed shape for lift and propulsion. In contrast, the bat’s highly elastic patagium and jointed fingers allow them to rapidly and continuously adjust the wing’s shape.
This control enables bats to perform complex aerial feats, such as making sharper turns and flying at lower speeds. This is beneficial for hunting insects in cluttered environments like forests. The flexible membrane generates lift and thrust during both the downstroke and a more complex upstroke.
However, this highly adjustable design often results in lower aerodynamic efficiency compared to the fixed-shape lift generated by a bird’s feathered wing. Consequently, birds can typically fly faster and migrate longer distances.