Hummingbirds are the smallest birds in the world and the size of raisins when they hatch. The tiniest species is Cuba's two-inch-long bee hummingbird.
They often double their body weight before migrating.
They can fly backwards and forwards, straight up and down, side-to-side, and are the only birds that truly hover.
They convert nearly 100 percent of the sugars they consume in nectar into energy -- one of the highest use-ratios of any food by any animal.
They have the largest heart and brain of any animal on earth in proportion to their body weight.
During flight, their hearts can beat 1,200 times per minute. The average human heart only beats 72 times per minute.
They fly at speeds up to 30 miles per hour.
Sources: Field guide to hummingbirds of North America by Sheri Williamson; Animal Diversity Web, the University of Michigan Museum of Zoology; Do Hummingbirds Hum? by Dr. George West; Dr. Susan Wethington, Executive Director, Hummingbird Monitoring Network