The hummingbird’s metabolism is so rapid that consumed sugars are used immediately to fuel the body.
Periods of torpor (rest with a low metabolic rate) ease the threat of starvation, but overall, they have to keep eating all day long to survive.
To survive long distance migrations (18-20 hour flight over the Gulf of Mexico), they bulk up their body fat ahead of time.
(SOURCE: empressofdirt.net)