Hummingbirds

Hummingbirds are the world's smallest birds (Bee Hummingbird: 5.7 cm, 1.6 g) and the only birds that can fly backwards. Their wings beat 80 times per second; their hearts beat up to 1,260 times per minute. In flight, they consume 10 times more oxygen per gram than athletes at maximum exertion. They can enter torpor (a deep sleep-like state) overnight to conserve energy. Hummingbirds have the best color vision of any animal — seeing into ultraviolet wavelengths invisible to humans. Many flowers have UV patterns visible only to hummingbirds, guiding them to nectar. They can remember every flower in their territory and calculate exactly how long it will take each to refill with nectar. Rufous Hummingbirds migrate 6,000 km each way — the longest migration relative to body size of any bird.