Focusing on flight:
* As light as a feather, soaring like a cloud.
* Like a paper airplane, gliding effortlessly on the wind.
* As swift as an arrow, piercing the sky.
* Like a kite, dancing on the breeze.
Focusing on appearance:
* As colorful as a rainbow, flitting through the trees.
* Like a jewel, sparkling in the sunlight.
* As delicate as a flower, perched on a branch.
* Like a tiny, feathered gem, hopping on the ground.
Focusing on sound:
* As melodious as a song, filling the air with music.
* Like a sweet chime, ringing through the forest.
* As cheerful as a whistle, greeting the morning.
* Like a soft whisper, echoing through the leaves.
Focusing on behavior:
* As busy as a bee, flitting from flower to flower.
* Like a curious child, exploring every nook and cranny.
* As free as the wind, roaming wherever it pleases.
* Like a fearless adventurer, navigating unknown territories.
The best simile will depend on the specific bird you are describing and the effect you want to create.