The term “flying squirrel” is misleading, as these nocturnal mammals are not capable of true, self-propelled flight like birds or bats. Belonging to the tribe Pteromyini, they are masters of arboreal acrobatics, using specialized membranes to perform long, controlled glides between trees. This ability allows them to efficiently navigate the high forest canopy, conserve energy, and escape predators in their habitat.
Gliding Versus True Flight
The distinction between gliding and true flight is based on the animal’s ability to generate its own thrust and lift to overcome gravity. True powered flight, which is limited to birds, bats, and insects, requires muscular power and an oscillating wingbeat to create sustained aerodynamic forces that propel the animal upward and forward. Gliding, by contrast, is an unpowered form of aerial locomotion that relies on gravity and air resistance. The animal launches itself from a height and uses its specialized body surface to catch the air, trading altitude for horizontal distance. Gliders are always moving downward relative to the air around them, even if the descent is gradual.
The Patagium and Gliding Mechanics
The physical adaptation that enables the flying squirrel’s impressive glide is a furry membrane of skin called the patagium. This membrane stretches laterally from the wrists of the forelimbs to the ankles of the hindlimbs. When the squirrel leaps and extends all four limbs, the patagium unfurls to create a large, parachute-like surface area. This expanded surface interacts with the air to generate aerodynamic lift and drag forces. Lift acts against gravity to slow the animal’s descent, while drag slows its horizontal speed.
The patagium is supported by skeletal elements, including a specialized, elongated cartilaginous projection from the wrist, known as the styliform cartilage. This cartilage helps stiffen the leading edge of the membrane, allowing the squirrel to maintain the necessary shape for an efficient glide.
Launch, Steering, and Landing
The active process of a glide begins with the squirrel launching itself from a high vantage point, such as a tree branch. It typically accelerates in a downward trajectory known as a ballistic dive, gaining forward momentum before deploying the patagium. Once airborne and the patagium is fully extended, the squirrel controls its path through subtle, precise movements of its limbs.
By changing the tension in the patagium and adjusting the angle of attack of its limbs, the squirrel modulates the lift and drag forces on each side of its body. This allows for mid-air steering, enabling turns and trajectory corrections to navigate around obstacles or toward a specific target. The long, bushy, and somewhat flattened tail acts as a stabilizer and rudder, providing additional control for pitch and yaw. Glides can cover distances of up to 90 meters (about 300 feet) in a single leap.
To prepare for landing, the squirrel executes a final maneuver called a pitch-up. It angles its body almost vertically just before reaching the target tree trunk, causing a rapid increase in lift and drag. This action effectively stalls the glide, which reduces its velocity and allows all four extended limbs to absorb the impact upon landing. This controlled deceleration minimizes the landing force, which can otherwise be several times the animal’s body weight.