Hummingbirds are among the smallest warm-blooded animals on earth. The bee hummingbird, a Cuban species, weighs less than a dime, and even middle-weight species like the rufous and broad-tailed hummingbirds weigh less than a nickel.
Their size makes them cute and also dictates their fretful, bickering, high-rev way of life. A hummingbird's heart beats more than 1,200 times a minute in flight; its wings hum at more than 2,000 revolutions per minute. This is why, even in the best of times, this fearless opportunist is a slave to its raging metabolism.
A typical hummingbird needs 7 to 12 calories a day. It gets most of them by sipping nectar from flowers. This sounds idyllic until you do the math: it's the equivalent of a 180-pound human having to scrounge up 204,300 calories a day, or about 171 pounds of hamburger. To keep itself alive, a hummingbird must manage to find as many as 1,000 flowers and drink almost twice its weight in nectar daily. It's enough to give even a very pretty little bird the personality of a junkyard dog. A scientific paper about the rufous hummingbird includes this endearing notation: "SOCIAL BEHAVIOR: None. Individual survival seems only concern."