Why did European explorers call the hummingbird the fly bird?

European explorers referred to the hummingbird as the "fly bird" due to its incredibly rapid wing beats, which can create a humming sound reminiscent of flying insects. The bird's ability to hover in place and dart quickly from flower to flower contributed to this nickname, as it seemed to flit about like a fly. Additionally, the explorers' observations of the bird's small size and agile movements reinforced this association.