Eight things packed into a hummingbird's tiny body.

Hummingbirds carry a fourth type of color cone, tuned to ultraviolet, that humans lack. In a 2020 field study, wild broad-tailed hummingbirds were trained to tell apart 'ultraviolet plus green' from plain green, light that looks identical to us. Where we see just one nonspectral color, purple, birds can perceive up to five, including ultraviolet-red and ultraviolet-yellow, letting feathers and flowers flash signals invisible to human eyes.

A male Anna's hummingbird climbs high, then plunges toward a female with wings folded, hitting about 27 metres per second, which is 385 of its own body lengths every second, the fastest length-for-length speed of any vertebrate. When it spreads its wings to pull out of the dive, it endures nearly nine times the force of gravity, more than a fighter pilot can take before blacking out, and shrugs it off.

The sword-billed hummingbird of the Andes is the only bird whose beak is longer than the rest of its body. The bill reaches 8 to 12 centimetres, while the body, minus the tail, is only 13 to 14, so the beak can out-measure the bird itself. It evolved to drink from deep trumpet flowers no other pollinator can reach, and is so unwieldy the bird must groom with its feet and perch with its bill tilted up.

Hummingbirds belong to the order Apodiformes, literally 'the footless ones.' Their legs and feet are so small and weak, and lack a working knee, that they cannot walk, hop or run; to shift even a few centimetres along a branch they must take to the air. The trade-off is total commitment to flight: feet built only to perch, scratch and grip, never to stride.

Most birds get lift only on the downstroke; the upstroke is dead weight. A hummingbird instead sweeps its wings in a horizontal figure-eight, twisting them over so they generate lift on the way back too. About 25 percent of its weight support comes from that upstroke alone. The two-way stroke is exactly what lets it hover in place, and fly straight backwards, like no other bird.

With a brain weighing under 0.2 grams, a hummingbird keeps a precise timetable of its world. Rufous hummingbirds tested with artificial flowers learned which blooms refilled after 10 minutes and which after 20, then timed their return visits to match, tracking not just where hundreds of flowers are but when each one is worth checking again, and flying memorised loop routes between them.

To beat its wings dozens of times a second and hover, a hummingbird is built around its engine. Its pectoral flight muscles make up 25 to 30 percent of its body mass, the largest proportion of any bird, where 15 percent is more typical. Packed with mitochondria filling up to a third of each muscle cell, those breast muscles give it one of the highest power outputs, pound for pound, of any vertebrate.