In 2011 Tyson Hedrick at the University of North Carolina in Chapel Hill studied the flight of the Ruby-Throated Hummingbird using high-speed X-ray cameras.  The study showed that a hummingbird flies more like a fruit-fly than a pigeon.  They twist their wrists to invert their wings allowing them to get lift on both the upper and lower sides of their wings.  Other birds flap their wings, only achieving lift on the lower side.  

This allows the bird to power their wings with small contractions of their chest muscles.