Why are flying squirrels not considered true fliers?

Flying squirrels are not considered true fliers because they rely on gliding rather than powered flight. While true flight involves active, sustained movement through the air—a capability found only in birds, bats, and most insects—flying squirrels use a specialized fold of skin called a patagium to sail downward from high vantage points.123

By leaping into the air and extending their limbs, these rodents stretch their membranes to create a gliding platform. This allows them to control their descent toward a target, but they lack the evolutionary modifications required for powered flight, such as the specialized wing structures, enlarged thoracic muscles, and skeletal adaptations found in animals capable of true flight. Instead, they utilize gravitational gliding to navigate between trees, effectively using their body surface area to manage wind resistance during their descent.123