The name “flying squirrel” often causes confusion, suggesting a capability for sustained, flapping movement like birds or bats. This generates a frequent question for those who observe the animal’s leaps through the forest canopy. To understand this locomotion, it is necessary to determine if the squirrel performs true flight or a different kind of aerial movement. The distinction lies in the physics of how the animal generates lift and forward motion.
Gliding vs. Powered Flight: The Key Distinction
Squirrels do not fly; they glide, which is a significant physical difference from powered flight. Powered flight, such as that performed by a bird or a bat, requires the animal to generate its own thrust through muscular effort, propelling itself forward to overcome drag and maintain or gain altitude. Gliding, conversely, is a form of unpowered flight where the animal relies entirely on gravity to provide forward motion.
A gliding animal begins at a higher point and trades its potential energy (height) for kinetic energy (forward speed). This descent is controlled by shaping the body to generate lift from the airflow, which reduces the rate of fall. This allows the animal to travel horizontally over a long distance. Without continuous thrust, the squirrel cannot flap its way upward or sustain a horizontal trajectory indefinitely. The movement is essentially a controlled, angled fall from one elevated point to another.
The Anatomy Enabling the Movement
The ability to glide is made possible by a specialized structure known as the patagium, a thick, furry membrane of skin. This membrane stretches along the squirrel’s side, extending between the wrist of the forelimb and the ankle of the hindlimb. When the squirrel extends its four limbs outward, the patagium pulls taut, creating a large, parachute-like surface area.
The patagium is structurally supported by specialized anatomy, including elongated cartilaginous extensions attached to the wrist (styliform cartilage). These structures help maximize the surface area of the gliding membrane by extending the ‘wing’ tip. The squirrel’s flattened tail also contributes to the aerodynamic profile, acting as a stabilizing surface. This combination of features transforms the squirrel’s body into an efficient airfoil, enabling it to harness air resistance for lift during its controlled fall.
Launch, Steering, and Landing: Executing the Glide
The gliding sequence begins with a launch, where the squirrel initiates a leap from a high vantage point, such as a tree branch. Almost instantly, it spreads its limbs to fully extend the patagium, creating the characteristic square or rectangular shape of the gliding surface. This rapid extension transitions the movement from a ballistic leap to an aerodynamically advantageous glide.
Once airborne, the squirrel controls its trajectory by making subtle adjustments to its body and the tension of the patagium. By changing the position of its limbs, it can modulate the lift and drag across the membrane, allowing for directional control, steering around obstacles, and even making turns up to 180 degrees. The flattened tail is employed as a rudder and stabilizer, aiding in mid-air maneuverability.
The final stage of the glide is the landing maneuver, which requires the squirrel to slow its descent to avoid impact. Just before reaching its target tree trunk, the animal pitches its body sharply upward, creating an aerodynamic stall. This rapid increase in the angle of attack dramatically increases drag, slowing the squirrel’s velocity for a soft, vertical landing. By distributing the landing force across all four extended limbs, the squirrel can safely absorb the impact, even though the force can be several times its own body weight.