ocr: FEATHERS PERFECTLY ADAPTED for the requirements of flight, feathers are unique to birds. Afeather is formed of a strong, light substance called keratin. The stiff, waterproof outer feathers are used for flight or streamlining. Underneath these lie soft, downy feathers that keep a bird warm. FEATHER VANE The flat areas on either side of the feather's shaft are called vanes NARROW LEADING VANE To help create lift, the leading vane is thinner than the trailing vane WIDE TRAILING VANE FLIGHT FEATHER BARBS A bird's flight feathers have a RACHIS hollow shaft with a vane on each The central shaft, si ...
