From: Andy Soos, ENN
Published June 23, 2011 03:49 PM

A Big Bird Flapping

How does a baby bird learn to fly? One anecdote is to push them out of the nest and hope they do not hit the ground. It is also similar o how a human baby learns to walk. The muscles have to grow strong enough to do the job. It can take months for their partially developed wings and flight muscles to become airworthy, and by then the youngsters are almost fully grown. However, long before their maiden flight, chicks probably put their developing wings to use, flapping as they run up steep branches. Brandon Jackson from the University of Montana, USA, explains that Ken Dial and his son first noticed this strange behavior when filming chukar chicks negotiating obstacles: instead of flying over, the birds ran up over the object flapping their wings. When Dial discussed this behavior with local ranchers and hunters, some described adult chukars flapping to run up cliffs. So why do adult birds flap and run up steep objects when they are perfectly capable of flying? Jackson, Dial and their colleague Bret Tobalske wondered whether pigeons might use 'flap running' to save energy, so they measured the amount of power generated by the flight muscles of flap running and flying birds and found that flap running birds use less than 10% of the energy of birds flying at the same angle.

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Birds are able to fly because of a variety of specialized adaptations. They have high metabolisms to supply their body with energy. They have lightweight bones. They have feathers that are long, strong, and able to produce lift and act as control surfaces. They also have a bone called the furcula, more commonly known as the "wishbone," in their chest, which is very important for being able to produce the strength and skeletal support needed to flap their wings.

The mechanics of flight are not unlike an airplane; the factors of lift, weight, thrust, and drag all interact to allow for controlled flight. By flapping their wings, birds create thrust and lift. They are able to steer by changing the shape and orientation of their wings and tail.

Wing-assisted incline running (WAIR) in birds combines the use of the wings and hindlimbs to ascend otherwise insurmountable obstacles. It is a means of escape in young birds before they are able to fly, and it is used by a variety of juvenile and adult birds as an alternative to flight for exploiting complex three-dimensional environments at the interface of the ground and air.

To test this assumption, the researchers measured several parameters and length change in the pectoralis (muscle) of pigeons as the birds engaged in shallow and steep WAIR and in three modes (angles)of slow flight immediately following take-off. Mean muscle stress, strain, work and power were minimal during shallow WAIR and increased stepwise from steep WAIR to descending flight and level flight to reach the highest levels during ascending flight.

The researchers concluded that WAIR remains a useful extant model for the evolutionary transition from terrestrial to aerial locomotion in birds because work and power requirements from the pectoralis increase incrementally during WAIR and from WAIR to flight.

Most paleontologists agree that birds evolved from small theropod dinosaurs, but the origin of bird flight is one of the oldest and most hotly contested debates in paleontology. The four main hypotheses are: "from the trees down" (They glided first), "from the ground up" (Early birds developed feathers for other reasons and then flew), WAIR and evolution from arboreal ambush tactics.

"At some point birds came from bipedal dinosaurs with small forelimbs that evolved into small wings," explains Jackson. Knowing that archaeopteryx's (the earliest known bird) flight muscles were probably too small to power flight, he suggests that they may have been large enough to help it flap run up steep obstacles. So, just as flap running appears to be a key stage in learning to fly, it could also have been a major breakthrough in the evolution of flight.

For further information: http://jeb.biologists.org/content/214/14/2354.abstract

Photo: http://thewebsiteofeverything.com/animals/birds/img/336-w/Chukar-Partridge.jpg

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