kite (bird)
鵈 refers specifically to a kite, a type of bird of prey. The meaning is narrow and concrete, centered on that particular bird.
鵈 is a phono-semantic compound: 鳥 (bird) gives the meaning, and 耳 (ear) likely contributes the sound. The exact historical development is uncertain, but the structure is typical for bird names.
The left side 耳 (ear) and right side 鳥 (bird) combine to suggest a bird known for its keen hearing, like a kite scanning for prey. Picture a kite with large ear-like tufts on its head.
For とび, imagine a kite soaring and then suddenly diving with a sharp 'toh-bee!' sound as it catches its prey. The sound 'toh-bee' cues とび.