cormorant
鷧 refers specifically to a cormorant, a type of water bird.
鷧 is a phono-semantic compound: 鳥 (bird) provides the meaning, and 壹 likely contributes the sound イ. The character was created to name the cormorant bird.
The right side 鳥 means bird, and the left side 壹 looks like a container with a lid. Picture a cormorant bird with a distinctive throat pouch, like a container for fish.
For イ, imagine an eagle (イーグル) that looks like a cormorant: eagle -> イ, and the bird 鷧 is a cormorant.