The video Watching Hummingbirds Watch 1998 explains that hummingbirds have evolved feathers unique to their species, namely, their wing tips reverse and so provide stationary lift, thus saving energy.

Also...in more or less direct flights (such as in migrations) hummingbirds are the fastest birds in the world in relation to their body length( over 300 body lengths per second, I think.) This is too fast for the human eye to frame and so they often appear to us as bright green streaks against a big blue sky.

When migrating, hummingbirds stop enroute to rest and feed, figgering, I guess, that if the lowly Monarch butterflies can flutter a thousand miles or so, the fastest bird in the world can too.