Small but speedy. Tiny but aggressive. Little bodies, big appetites. Hummingbirds are a study in extremes. They are the lightest North American birds. Most weigh less than two pennies at 3 to 4 grams.

Add Yahoo as a preferred source to see more of our stories on Google. Hummingbirds have one of the highest metabolic rates of any vertebrate. They are the only birds capable of sustained backward ...