and for a detailed technical/engineering analysis by the same group see here:
They compare hummingbird hovering with the advanced military Black Hornet micro-helicopter :
The wing shape (width/length ratio) is similar in both hummers and microhelicopters (and much less slender than in regular helicopters. Obviously the wing movements are quite different in the 2 cases: the hummingbird wing flaps and the microhelicopter wing rotates, but this difference is not fundamental: the hummer wing generates lift on both down- and upstrokes by changing the angle of attack (by swiveling the wing) and the rotor instead maintains the same attack angle consistently by continuous swiveling. Nevertheless the paper concludes that the hummingbird is about 27% more efficient than the microhelicopter.
Meanwhile here are more examples (including a Cloudless Sulfur and an American Lady) of the more leisurely flight of butterflies at the sanctuary