Page 46 - The Origin of Birds and Flight

44 The Origin of Birds and Flight

Dial’s thesis was based on some observations of partridges of the
species Alectoris chukar. When these birds ascend a steep slope or tree
trunk, they prefer to run rather than climb and, as they run, flap their
wings for greater speed. This short sprinting is known as “wing-assisted
incline running.”
During this process, the partridges use their wings as well as their
feet, thus reducing the effect of gravity. This bird’s feet are created in
such a way as to grip the ground, and its wings act rather like the ailer-
ons on a racing car. Based on this evidence, Dial maintains that the first
birds, similarly, used their wings not for flight, but to assist in running.
He hypothesizes that these animals moved their forelimbs not forward
and backward like reptiles, but up and down, like modern-day birds.
With this proposed concept, Dial aimed to find a compromise path
between the two sides of the debate over the origin of flight, which had
been going on since the 1800s: of whether dinosaurs learned to fly by
30
running on land or by leaping from tree to tree. However, this claim of
his received little approbation. Luis Chappe of the Los Angeles Natural
History Museum summed the matter up by saying that we could never
know whether or not dinosaurs behaved like partridges:

I imagine people will continue to argue about the origin of bird flight for
a long time. 31

Dial observed that young birds were almost as talented as adults
when it came to wing-assisted incline running. He established that only
four days after they hatched, youngsters were able to climb 45-degree
inclines in this manner, and that their still-growing wings
created an aerodynamic effect. He conducted a number
of experiments on these wings and saw that the aer-
odynamic effect declined in those wings whose
developing feathers he shortened. These birds
were unable to climb as well as those whose
feathers had not been shortened. Tests in the
laboratory showed that various other ground-
dwelling birds—such as the partridge, chicken,