10 centimeters!
Hummingbirds are small birds of the Americas that feed mainly on nectar from flowers and can hover in place and fly backward. The hummingbird in the explorer is 10 centimeters (4 inches) long from the tip of its bill to the tip of its tail, about the length of an Anna's hummingbird. Most of the more than 300 species are 6–12 centimeters (2.4–4.7 inches) long.
Most hummingbird species weigh 2.5–6.5 grams. The smallest is the bee hummingbird of Cuba, which is also the smallest known bird. Males average 5.5 centimeters long and 1.95 grams, and females 6.1 centimeters and 2.6 grams. The largest, the giant hummingbird, weighs 19–21 grams, about ten times as much as a male bee hummingbird.
Two familiar North American species show the usual range. The ruby-throated hummingbird of the eastern United States is 7.5–9.0 centimeters (3–3.5 inches) long and weighs 3.4–3.8 grams. Anna's hummingbird, which lives all year along the Pacific coast, is about 10 centimeters long and weighs 4–4.5 grams. Its wings span 11.4–12.1 centimeters (4.5–4.8 inches).
Hummingbirds hover in front of flowers while they feed, and they can fly forward and backward. Small species beat their wings 70–80 times a second, and the giant hummingbird 10–15 times. In forward flight they can reach 45 kilometers per hour (28 miles per hour).
Flying like this takes a great deal of energy. A hummingbird's heart beats 500–600 times a minute at rest and more than 1,000 times a minute when it is active. Hummingbirds can drink up to twice their body weight a day, and they catch insects for protein.
On cold nights, hummingbirds save energy by going into torpor, a state in which the body cools and slows down. Their heartbeat can drop below 50 beats a minute. Coming out of torpor can take as long as an hour.
Hummingbirds live only in the Americas, from Alaska and Labrador in the north to Tierra del Fuego at the southern tip of South America. Most species live in Central and South America. Some migrate long distances, and those that cross the Gulf of Mexico make a non-stop flight of 18–22 hours.