the miracle of bird flight -- 10/11/16

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Today's selection -- from Birdology by Sy Montgomery. The flight of birds is an extraordinary feat, requiring a miraculous combination of attributes. The king of flight is the hummingbird:

"Bird flight is a confluence of miracles: Scales evolved into feathers. Mar­row gave way to air. Jaws turned to horny, lightweight beaks bereft of teeth. (This is why many birds swallow stones: to grind their food since they can't chew lt.) Hands grew into wingtips. Arms became airfoils. 'The evolution of flight has honed avian anatomy into an extreme and remarkable adaptive configuration,' anthropologist Pat Shipman writes in her wonderful book Taking Wing: Archaeopteryx and the Evolution of Bird Flight. But while most birds are made to fly, and the urge to fly is instinctual, flight itself must be carefully and painstakingly learned -- a task of impressive complexity.

"Consider the three basic methods of bird flight. The simplest, gliding flight, demands exquisite balance and judgment. Gliding flight exploits pas­sive lift to counteract the pull of gravity. Vultures, hawks, and eagles ride the currents within thermals, rising columns of warm air. Albatrosses and petrels exploit different layers of wind speed above waves. Birds can glide for hours, expending very little energy.

"Flapping flight -- the way most birds fly -- is more demanding still. Achieved by flexing wings at joints in wrist, elbow, and shoulder, it is pow­ered by extraordinarily strong breast muscles. The wings move forward in a downward arc, propelling the bird forward and up. It is similar to the oars­man's power stroke or the action of a swimmer doing the butterfly. Move­ment then flows into the upward stroke, a recovery stroke, to start the process anew.

"And finally, there is hovering, unique to hummingbirds. No other bird really hovers --kites, storm petrels, kestrels, and kingfishers appear to do so, but only hummingbirds can sustain this method of flying for more than a few moments. Instead of flapping the wings up and down, the wings move forward and backward in a figure eight. During the forward and back strokes, the wings make two turns of nearly one hundred and eighty degrees. The upstroke as well as downstroke require enormous strength; every stroke is a power stroke. Like insects and helicopters, hummingbirds can fly back­ward by slanting the angle of the wings; they can fly upside down by spread­ing the tail to lead the body into a backward somersault. Hovering becomes so natural to a hummingbird that a mother who wants to turn in her nest does it by lifting straight up into the air, twirling, then coming back down. A hummer can stay suspended in the air for up to an hour.

"Hummingbirds are specially equipped to perform these feats. In most birds, 15 to 25 percent of the body is given over to flying muscles. In a hummingbird's body, flight muscles account for 35 percent. An enormous heart constitutes up to 2.5 percent of its body weight -- the largest per body weight of all vertebrates. At rest, the hummingbird pumps blood at a rate fifteen times as fast as that of a resting ostrich, and that blood is exception­ally rich in oxygen -- carrying hemoglobin. 'There can be no doubt it reigns supreme over all the other birds of the world,' writes Esther Tyrrell, 'and truly deserves to be called the champion of flight.'

author:	Sy Montgomery
title:	Birdology: Adventures with Hip Hop Parrots, Cantankerous Cassowaries, Crabby Crows, Peripatetic Pigeons, Hens, Hawks, and Hummingbirds
publisher:	Free Press
date:	Copyright 2010 by Sy Montgomery
pages:	78,79, 90, 91