Meaning: This sentence describes the way the feathers of birds move in the morning breeze. It's like saying, 
Choice of Words: "Feathers" are the soft, light structures that cover the body of a bird. "Flutter" means to move quickly and lightly. "Gentle" means kind and not harsh. "Morning breeze" is a light wind that blows in the morning. When you put it together, it means the feathers of birds move quickly and lightly in the gentle wind that blows in the morning.