This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鴗 combines 立 (stand) and 鳥 (bird). The exact historical development is uncertain, but it likely represents a specific bird name.
A bird 鳥 standing 立 still, perhaps a kingfisher watching for prey. The shape suggests a bird in a poised, upright posture.
For リュウ, imagine a kingfisher named Ryu standing by the water: Ryu -> リュウ, and the bird 鴗 waits patiently.