Humming birds are very challenging targets if you reallly want to have a couple of good shots of them. This spiece in particular is very small and shares its territory with much bigger hummers, which are far more agresive (e.g. Sparkling violetear). That´s the reason why this small hummer is a very skilled flyer and extremly fast.
It approches to the flower allways very carefully in order to avoid confrontations.