As the world's smallest birds, hummingbirds have a high
surface-area-to-volume ratio. That means they lose a lot of heat
through their skin. The problem is compounded by a lack of downy feathers,
the fluffy insulation that keeps most birds warm. Skipping the down
shaves weight, but the birds must compensate by refueling constantly,
consuming two or three times their body weight every day.
Hummingbirds’ “fighter-jet” acrobatics are as dazzling as their
plumage, but the same physics that sets them apart exacts a steep price.