It’s been my experience that the smaller someone is, the more dangerous they can be. The worst cop on any police force is always the one who barely made the height requirement. So it’s no surprise that tiny birds are the meanest.
Slate has a good article about Hummingbirds and their place in Aztec culture.
Huitzilopochtli is the Aztec god of war and the sun. He is depicted either as a hummingbird itself, or as a warrior with hummingbird feathers on his helmet. When Aztec high priests cut out the hearts of enemies and slaves, it was to honor and feed the hummingbird god. (If Huitzilopochtli was happy and fed, the Aztecs would be triumphant in war and conquest.)
The Aztec were well aware of how mean these birds could be. It’s easy to forget that perspective of size, when your feeder has a delightful little green visitor.