A widely known story tells how the nighthawk came to have such a big mouth. The trickster nih’oo3oo, as usual, had gotten himself into trouble: a rock had rolled on top of him and pinned him to the ground. He begged for help. The nighthawk (also called ‘bull bird’) came and flew down at the rock. Each time he swooped past the rock, he ‘farted.’ (Nighthawks make a low, thrumming sound as wind whistles through their wings, as part of their display behavior. The Arapahos call this ‘farting’.) Gradually the farts chipped the rock away until nih’oo3oo could escape. He called the nighthawk over to thank him, but then grabbed the bird and pulled his mouth very wide open. No one seems to know why he did this, but this is why the nighthawk has such a big mouth.
Nighthawks were also seen as indicative of rain, since they fly before thunderstorms (Kroeber, The Arapaho, p. 434).