Left radical 口 - a small open square, marking 嗷 as a sound that comes out of the mouth: a wail, a howl, a yelping cry. Same radical anchors a huge family of vocal sound-effects and onomatopoeia: 哭 (cry), 叫 (shout), 喊 (yell), 哼 (snort), 啊 (ah).
Right phonetic 敖 supplies the full sound áo with no drift. The character originally meant 'to roam, to be lordly', here used purely for sound. Same phonetic produces 傲 (proud), 熬 (simmer/endure), 翱 (soar), 遨 (roam) - all with áo as the head sound.
