Translation:Duo is a smart owl.
When writing out English expressions, the Chinese are more concerned with how the word sounds than with how it looks spelled out. Ex: Amelia Earhart = ā méi lì yà · āi ěr hā tè (阿米莉亚·埃尔哈特) which spelt out looks nothing like Amelia Earhart but sounds like it when you say it out loud. If they just said "duo," it would miss out on the "oh" sound at the end of the word. "er" is the closest they can get.