The aerial acrobatics of a hummingbird are as much a marvel as its blinking, iridescent colors. You may have seen a hummer feeding on tubular flowers that point in all directions. Its wings are blurs as it hovers at one flower while probing it for nectar. When finished drinking, it moves straight backwards to remove its bill from the flower, hovers momentarily, and then plants itself in perfect feeding position at the next flower. It easily changes position up or down to reach higher or lower flowers. A flower pointing sideways is no problem. The hummer simply hovers with its body at a slight incline. A flower hanging downward is conquered by holding its body totally vertically and directing its bill straight up. It can pivot 360 degrees to assess the presence of interloping hummers or predators. It can fly upside-down by doing a backward somersault, then darting along with its wings in reverse and its feet upward. All in all, the hummingbird is as comfortable in the air as a fish is in water. About the only thing a hummingbird can’t do in the air is soar for long periods without flapping its wings. This requires a larger bird with larger and broader wings.
A hummingbird reaches close to full speed the moment it begins to fly. It does not push off of and spring forward from a perch. A slender branch lifts up with the bird as it leaves. Similarly, it has no need to slow down when landing. Such abrupt stops would be fatal for heavier birds or airplanes.
The overwhelming majority of hummingbirds use their miniature feet to perch or grasp, but not to walk or hop. They are rarely, if ever, seen perching on the ground. To move a few inches on a branch, they fly. Their wings are their only source of locomotion.
When nesting, the hummer flies right into the nest. There is no need to perch on the rim first like most other birds would. By the time the wings are folded, the hummingbird is already incubating her eggs or covering her young. Likewise, when leaving some hummers start beating their wings while still sitting on the eggs or nestlings. They fly upward and backward until clear of the nest, then pivot and dash away. A hummer does not stand up to turn around in its nest. Instead, she beats her wings and rises up, then pivots in the air.
How do they do these things? The anatomy and physiology of their wings and flight muscles make such flight possible. The bones and joints in a bird’s wing roughly correspond to those in our shoulders, arms, elbows, wrists, and hands. All birds, except hummingbirds, move their wings at the shoulder, elbow and wrist. Powerful pectoral muscles move the whole wing up and down from the shoulder. The inner part of the wing acts as a handle for the propelling outer wing (from the wrist out). So most birds move their wings at the shoulder, elbow, and wrist. Flight for all but hummers really occurs from the wrist out, on the outer wing, with the help of its long primary flight feathers.
Hummingbirds are constructed differently. Their wings are virtually all “hand”. The other parts are all there, but they are much smaller. The short arm bones of the hummer form a rigid “V” because the elbow and elbow wrist joints are inflexible. All wing movement comes completely from the shoulders. The shoulder joint is extremely mobile. It permits more free movements than our own shoulder as hummingbirds can axially rotate their wings 180 degrees. (While some of us can revolve our hands 360 degrees, the forearm does most of the rotating, not the shoulder.)
This exceptionally supple shoulder makes the remarkable flight of the hummer possible. In most birds, lift or propulsion occurs only on the downstroke. The upstroke is made with the wings partly folded and the primaries separated to decrease air resistance. It is not a heavy contributor to the bird’s progress. For hummers, the rigidly extended wings are twisted to obtain lift on both the forward and backward strokes. The front edge of the wings leads on both strokes. On the backstroke, the wing is turned completely over so that the underside of the feathers faces upward, and the front edge is still leading. When hovering, the hummingbird actually moves its wings in a figure eight pattern that is lying on its side. The rapidly beating wings move forward and backward rather than up and down. While both forward and backward stokes do provide lift, they cancel any tendency to move forward or backward, and the little bird hangs poised in the air.
Other adaptations have occurred to accommodate the hummingbird’s unique method of flight. The sternum or breastbone is proportionately larger and more deeply keeled than other birds. Eight pairs of ribs (most land birds have six) protect it from the great stresses of hummingbird flight In most birds, the muscles that control the upstroke (elevators) are smaller and weaker than those that control the propelling downstroke (depressors). Since power is generated on both upstroke and downstroke in hummers, the “elevator” muscles are much larger and more powerful than in other birds. These elevator and depressor flight muscles account for up to 30% of a hummingbird’s weight. Other birds only invest 15% to 20% of their body weight in flight muscles.
During flight, hummingbirds need huge amounts of oxygen. This places considerable strain on their circulatory system. To meet this need, they have the largest known relative heart size of any bird (up to 2.4% of total body weight). In concert with this, they have the fastest heartrate of any bird (up to 1,260 beats per minute). A three gram hummingbird breathes about 250 times per minute.
Contrary to popular belief, for the length of their wings and their weight, hummers do not beat their wings more rapidly than other birds. At a given speed, a small body appears to move faster than a larger one, but this is an optical illusion. Many hummers that weigh 5 to 7 grams beat their wings 20 to 25 beats per second. The chickadee is twice as heavy, but it beats its wings at 27 times per second. Since the chickadee relies only on the downstroke for its power, while the hummer efficiently generates power on both upstroke and downstroke, 25 hummingbird wing beats would equal 50 chickadee wing beats.
Speed for hummers has been measured at 27 m.p.h. in a wind tunnel, and up to 60 m.p.h. during courtship. With incredible flight control, hummers were clocked in a 74 yard figure- eight course in an aviary at 30 to 47 m.p.h. Songbirds, including those as big as thrushes, fly at 25 to 35 m.p.h.