Linked from
The 21 pages that link to Gliding flight, each with the reason it gives.
GliderNarrower topic: A glider is an aircraft designed to make this unpowered flight efficient.
Flying squirrelNarrower topic: Flying squirrels use this form of flight to cross gaps between trees.
PatagiumNarrower topic: Many patagia generate aerodynamic support during unpowered glides.
ColugoNarrower topic: Colugos use aerodynamic glides to cross gaps between trees.
SharovipteryxNarrower topic: Sharovipteryx is interpreted as a glider rather than a powered flyer.