A nightjar or similar nocturnal bird, especially the common nighthawk; named for the loud humming sound of its diving flight.
From 'bull' (suggesting the deep sound) plus 'bat' (confusing nocturnal birds with bats). The name describes the creature's distinctive booming sound during its nighttime aerial displays.
Bullbats were mysterious birds to early Americans who heard strange humming and booming in the night sky—they named them based on sound, not sight, which is why the name is so perfectly evocative!
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