National Geographic : 2017 Jul
112 national geographic • July 2017 Lift Airflow Downstroke 100% of the lift Upstroke 0% of the lift Downstroke 75% of the lift Upstroke 25% of the lift Bee hummingbird 1.7 inches long Common pigeon 11-14 inches long Elbow Wing tip Actual size Lentiformis mesencephali .25% Percentage of total brain volume Part of the brain Lentiformis mesencephali .07% Hippocampus 4% Hippocampus 7% Hand wing is around 75% of total wing area top view top view Wrist Hand wing Arm wing Elbow Shoulder Hand wing is around 50% of total wing area ArmwingHandwing Shoulder Wrist Majesty in Miniature Unlike other birds, such as pigeons, a hummingbird can fly in multiple directions, including backward and sideways. Its wings can beat up to a hundred times per second. Its brain, at 4.2 percent of body weight, is pro- portionally one of the largest in the animal kingdom. his own. He filmed the flight of hummingbirds inside a homemade wind tunnel, capturing them at speeds up to 27 miles an hour. As the birds ac- celerated from a hovering position, Greenewalt documented the plane of their wings tilting from horizontal to vertical, redirecting their thrust. The new images were groundbreaking, but they didn’t solve the mystery of how humming- birds can flap their wings as quickly as they do. Typically, the faster a muscle contracts, the less force it generates. So how do hummingbirds pro- duce enough force to stay aloft? In 2011 Tyson Hedrick and his colleagues jury-rigged a way to answer that question. A University of North Carolina at Chapel Hill re- searcher who specializes in animal biomechan- ics, Hedrick knew that hummingbird wings are different from those of their closest relatives, the swifts. Hummingbird arm bones are relatively smaller, and most of the wing is made up of the equivalent of hand bones. To get a penetrating view of the wing moving at top speed, Hedrick coupled a camera that shoots a thousand frames per second with an x-ray imaging system. When Hedrick viewed the frames in sequence, infinitesimal movements of the wing bones merged into patterns, then continuous motion, and the wing’s operation could be seen. Rather than flapping with an up-and-down motion of the shoulder, Hedrick discovered, humming- birds flap with a twist. This modification gives them what amounts to a “high gear,” so that a millimeter-length muscle movement is enough to drive their wings across a wide arc. Once, high-speed cameras were ungainly con- traptions, difficult to operate and lug into the field. Now they can fit in a large pocket and are as essential to hummingbird biologists as binoc- ulars are. The sheer magnitude of information captured by these cameras can be hard to fathom. To put Clark’s 500-frames-per-second videos in perspective, consider this: At the typical frames- per-second rate of a theatrical movie—let’s say, the 1939 classic Gone With the Wind—500 frames is roughly what it took for Scarlett O’Hara to run down the staircase, tearfully plead, “Rhett, Rhett! If you go, where shall I go? What shall I do?” and Hovering hummingbirds Hummingbirds produce lift with both upward and downward wing strokes, creating vortices that help with hovering and maneuverability. Forward-flying pigeons Larger birds such as pigeons use wing downstrokes to push air jets down and behind them, propelling them forward.