Doubling Their Weight
Before migration, hummingbirds go on a feeding frenzy. They feed often and intensely for days, a state called hyperphagia. The tiny birds double their weight, gaining the fat they need to fuel their long journey. The extra fat, called yellow fat, deposits around the hummer's body cavity and organs. The stored fat provides more than twice the energy per gram than burning carbohydrates or protein. Yellow fat metabolism produces twice as much water than burning protein or carbs which provides sufficient protection from dehydration during long flights. Ornithologists calculated that hyperphagia generates enough fuel for a hummingbird to fly nearly 600 miles at 35 miles per hour.

John D. of Bellingham, WA
Hummingbird: Doubling Weight