Hummingbirds, like all flying birds but more so, have incredible enormous immense ferocious metabolisms. To drive those metabolisms they have race-car hearts that eat oxygen at an eye-popping rate. Their hearts are built of thinner, leaner fibers than ours. Their arteries are stiffer and more taut. They have more mitochondria in their heart muscles—anything to gulp more oxygen. Their hearts are stripped to the skin for the war against gravity and inertia, the mad search for food, the insane idea of flight. The price of their ambition is a life closer to death; they suffer more heart attacks and aneurysms and ruptures than any other living creature. It’s expensive to fly. You burn out. You fry the machine. You melt the engine. Every creature on earth has approximately two billion heartbeats to spend in a lifetime. You can spend them slowly, like a tortoise and live to be two hundred years old, or you can spend them fast, like a hummingbird, and live to be two years old.
The American Scholar: Joyas Volardores - Brian Doyle. Several times over the years I have come across hummingbirds lying in the leaves or on the grass, perfectly formed, beautiful as creatures can be, not a mark on them, and stone-dead.