"They're not birds! They're keys! Winged keys -- look carefully. So that must mean ... yes -- look! Broomsticks! We've got to catch the key to the door!"
-- Harry Potter, cottoning on (PS16)
A flock of winged keys were one of the protections for the Philosopher’s Stone, put in place by Filius Flitwick. The swarm of winged keys filled a well-lit chamber blocking the way to the hiding place of the Mirror of Erised and the Philosopher’s Stone within. The keys had shiny, brightly colored wings which glittered like jewels. One particular key, an old-fashioned silver key with bright blue wings, was needed to open the heavy wooden door leading into the next chamber. In order to pass through, a person had to mount a broomstick and fly to catch the proper key (PS16).