seagull, tern
鷗 centers on a specific type of seabird: a seagull or tern, often seen near coasts.
鷗 combines 鳥 (bird) with 區, which likely contributes the sound and may have originally depicted a specific bird-related concept. The exact historical development of 區 in this character is uncertain.
The left side 區 looks like a container or area, and the right side 鳥 is a bird. Imagine a coastal area where seagulls gather: 鷗 is that seagull.
For オウ, picture a seagull flying over the ocean and letting out a loud 'Oh!' call: Oh -> オウ, the sound of the seagull.
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