The "Idiot Bird"

Whilst preparing for an upcoming article about the Japanese version of Samuel Taylor Coleridge's Rime of he Ancient Marine, I encountered the Japanese name for the albatross within the text.

信天翁

Literally "believe heaven venerable-oldster", which frankly does sound like a respectable name for the albatross that figures heavily in the story as a symbol of woe and blessing.

The name appears, derived from the Chinese name that is spelled the same, to be referring to it appearing to entrust its fortunes to the heavens, hence "believe heaven oldster"

So, how do you then pronounce the name of this waterfowl?

あほうどり (ahoudori, lit. "idiot bird")

あほう (ahou) is a dialectal Japanese term variously translated as "idiot" or "fool", but all in all in this avian name refers to the bird's ungainly size and apparent clumsiness, when in flight.

What happened with the kanji, whose reading would usually be しんてんおう (shinten'ou), which is an actual proper reading, if uncommon for the characters?

As with most zoological names in Japanese, it is a case of a native Japanese word being paired with an already existing or descriptive kanji name, often such words are called jukujikun, i.e. the kanji are used purely for their meaning rather than reading - the opposite would be ateji, where the kanji lend their reading rather than meaning.

Such as for the cuckoo there's 時鳥 ("time bird") read as ほととぎす (hototogisu), presumably in imitation of the bird's call.