And due to these characteristics they don't appear to have any natural predators. Their agility is also legendary. They are the only type of bird that can fly backwards, and this dexterity allows them to feed from hanging flowers while hovering back and forth, something no other bird is able to do.
Due to their small size, their bodies lose energy at a very fast rate, and they have to eat more relative to their body weight than other birds just to survive. These birds live on the brink of physical existence - if they were any smaller, it wouldn't be possible for them to eat enough to make up for the lost energy.
Relative to their body mass, their hearts are the largest of any bird. Their high metabolic rate is fuelled by a very high heartbeat, measuring 1200 beats per second while flying. Their respiratory and circulatory systems are equally efficient - they can breathe more than250 times per minute, thus providing a large amount of oxygen to their muscles transported by their red blood cells.
Hummingbirds are not able to eat enough to power their bodies for a full 24-hour period. In order to conserve energy they go into a nightly hibernation. They enter a. state of torpor such that when they're asleep, their body temperature drops, their heart rate slows and their breath is almost impossible to detect. A couple of hours before daybreak, almost as if a switch goes off in their brain, something flickers and the birds start to shiver. It takes around twenty minutes of shivering before the birds to get their energy level back up so they can start their daily search for breakfast.
Despite the adorable image we have of hummingbirds, ounce for ounce they're probably the fiercest creatures on earth. Male hummingbirds can be very aggressive when claiming new, and defending existing, territories.
So fierce are hummingbird battles that the Aztecs believed their dead warriors were reincarnated hummingbirds. And that's how the most powerful Aztec God, Huitzilopochtli, had the hummingbird as his spirit animal.