Final answer:
Developing flight feathers enable a fledgling to flutter from branch to branch. These feathers, along with a bird's lightweight skeleton, high metabolism, and lack of teeth, are all vital traits that support the ability to fly.
Step-by-step explanation:
What enables the fledgling to flutter from branch to branch is its developing flight feathers. These feathers are crucial as they produce the lift and thrust necessary for flight. Birds also have a lightweight but strong skeleton with hollow bones, and high metabolism, which contribute to the ability to fly.
Additionally, other traits important for flight include a four-chambered heart that supports the high metabolism needed for flying and a beak with no teeth which reduces overall weight. Birds have made several adaptations to reduce body weight, such as possessing one ovary and lacking teeth, which is essential for an efficient flying experience.