wild goose
鳫 centers on a wild goose, a migratory waterbird. The meaning is specific to this bird, with no broader abstract extensions.
鳫 combines 厂 (cliff) with 鳥 (bird), likely depicting a goose near a cliff or in a wild setting. The exact historical development is uncertain, but the component combination is consistent with the meaning.
A bird 鳥 under a cliff 厂: picture a wild goose nesting on a rocky ledge. The cliff and bird together make 鳫, the wild goose.
For ガン, imagine a wild goose honking a loud 'GAN!' as it flies off the cliff. The honk 'GAN' cues ガン, and the goose under the cliff is 鳫.