This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鸙 combines 龠 (a flute-like instrument) with 鳥 (bird). The exact historical development is uncertain, but it likely referred to a bird associated with music or a specific bird name.
The kanji visually contains a flute 龠 and a bird 鳥. Imagine a bird that sings like a flute, but its exact meaning is uncertain.
For ヤク, imagine a yak playing a flute for a bird: yak -> ヤク, and the bird sings along.