dove, temple pigeon
鴿 centers on a specific kind of bird: a dove or temple pigeon. The meanings are closely related, both referring to the same gentle bird often associated with peace or sacred spaces.
鴿 combines 合 (meeting, fitting) with 鳥 (bird), likely forming a phono-semantic compound where 合 suggests the sound and the bird radical indicates the meaning. The exact historical development is uncertain.
The left side 合 can suggest a meeting or gathering, and the right side 鳥 is a bird. Picture doves gathering peacefully at a temple, cooing softly together.
For コウ, imagine a dove cooing softly: the coo sound cues コウ, and the dove is the bird on the right.