The mysterious hoopoe

There are some parts of the Bible which provoke questions that are clearly not essential for salvation.

The sort that, if mentioned in passing by a preacher, would distract me from the main point of the sermon, almost as if I spotted an extremely rare bird out of the window.

My Bible reading plan recently brought me to the list of clean and unclean food in Leviticus 11, where I got hopelessly distracted by the list of birds in verses 13 to 19. Ignoring the other provoking question of why the list ends with a bat, which is not a bird at all, the big question of course is why the hoopoe is regarded as unclean?