Crazy as a loon

Crazy as a loon

I assume that you were asking for the origin of the phrase.

What in (English-speaking) Europe is called the Great Northern Diver is called in North America the Common Loon (a species of bird). It has a weird, haunting cry which presumably suggested to someone the howls of the insane. Hence, crazy as a loon.

DFG

One reason that that odd, sort of laughing, sound made by loons makes such an impression is that it sometimes does it at night, when most birds are silent. Kinda spooky. SS