Protowings in BioScience

["bh480@scn.org" <bh480@scn.org>]

From: Ben Creisler bh480@scn.org
In case this article has not been mentioned yet:

What Use Is Half a Wing in the Ecology and Evolution of Birds? 
Authors: Dial, Kenneth P.; Randall, Ross J.; Dial, Terry R.
Source: BioScience , Volume 56, Number 5, May 2006, pp. 437-445(9)
Abstract:
The use of incipient wings during ontogeny in living birds reveals not only
the function of these developing forelimbs in growing birds' survival but
also the possible employment of protowings during transitional stages in
the evolution of flight. When startled, juvenile galliform birds attempt
aerial flight even though their wings are not fully developed. They also
flap their incipient wings when they run up precipitous inclines, a
behavior we have described as wing-assisted incline running (WAIR), and
when they launch from elevated structures. The functional benefit of
beating these protowings has only recently been evaluated. We report the
first ontogenetic aerial flight performance for any bird using a ground
bird, the chukar partridge (Alectoris chukar), as a model species. We
provide additional ontogenetic data on WAIR, a recently described locomotor
mode in which fully or even partially developed flapping forelimbs are
recruited to increase hindlimb traction and escape performance. We argue
that avian ancestors may have used WAIR as an evolutionary transition from
bipedal locomotion to flapping flight. 
http://www.ingentaconnect.com/content/aibs/bio/2006/00000056/00000005/art000
11;jsessionid=ouqha0pv5v7l.victoria


Also see:
http://www.eurekalert.org/pub_releases/2006-05/aiob-pmh042106.php
Protowings may have helped bird ancestors cover rough terrain
Even wings that are still in development help living birds gain traction on
slopes and scale obstacles
Biologists have long argued about how birds evolved the ability to fly,
because it is not immediately evident what improvement in fitness would
result from ancestral, partly evolved wings. Two theories have recently
dominated the debate: one postulates that flight evolved in tree-dwelling
ancestors that used their forelimbs to help them glide, while the other
considers ancestral birds to be terrestrial dinosaurs that developed
powered flight from the ground up. 
An article by Kenneth P. Dial and two co-authors in the May 2006 issue of
BioScience summarizes experimental evidence indicating that ancestral
protobirds incapable of flight could have used their protowings to improve
hindlimb traction and thus better navigate steep slopes and obstructions.
By using their protowings in this way, they would presumably have had an
advantage when pursuing prey and escaping from predators. 
Dial and colleagues performed experiments on several species of juvenile
galliform (chicken-like) birds, concentrating on chukar partridges. Chukars
can run 12 hours after hatching, but they cannot fly until they are about a
week old. Even before they are able to fly, however, the birds flap their
developing wings in a characteristic way while running, which improves
their ability to climb steep slopes and even vertical surfaces. Dial and
colleagues have named this form of locomotion "wing-assisted Iincline
running" (WAIR). After they are able to fly, chukars often use WAIR in
preference to flying to gain elevated terrain, and exhausted birds always
resort to WAIR. 
Dial and colleagues describe experiments showing that if the surface area
of chukar wings is reduced by plucking or trimming the feathers, WAIR
becomes less effective for climbing slopes. Dial and colleagues propose
that incipiently feathered forelimbs of bipedal protobirds may have
provided the same advantages for incline running as have now been
demonstrated in living juvenile birds. Their work thus supports a new
theory about the evolution of flight in birds. WAIR, which the authors
believe to be widespread in birds, appears to offer an answer to the
question first posed by St. George Jackson Mivart in 1871: "What use is
half a wing?" 


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