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Re: Birds ignore physics to fly in 3rd gear



Dann Pigdon wrote:
"Birds ignore physics to fly in 3rd gear"
Larry O'Hanlon, Discovery News
SNIP
Read more at:
http://www.abc.net.au/science/news/stories/2007/1985386.htm

Interesting news article. Includes this as the final part:

"What's more, he says, the real world is always changing in unpredictable ways that require birds to adapt to keep pace or die out. Few adaptations that help different birds survive also make them the best flyers. It's an example of what's called the Red Queen Hypothesis, says Tobalske, referring to the character in Lewis Carroll's /Through the Looking Glass/."The Red Queen is running just to stay in place," Tobalske says."Evolution does the same with birds: keeping them in constant evolutionary motion but never allowing them to get any closer to aerodynamic perfection"

Well, I choked on my coffee at that one. It's an example of phylogenetic constraint, I say to myself. For the Red Queen hypothesis to be supported by large-scale, biomechanical analysis would be news indeed. So I had a look at the original paper on PLoS http://biology.plosjournals.org/archive/1545-7885/5/8/pdf/10.1371_journal.pbio.0050197-L.pdf
and this chap Tobalske isn't on the author list. Says an earlier part of the the news article:
"Often people think that animals are optimised," says US bird flight researcher Bret Tobalske, a professor at the University of Portland <http://www.up.edu/>. "[But] they evolved from ancestors that didn't fly."


An interesting statement in itself, but anyway, I'm hunting down Carrolian heresies by now, so I let that one go and scan the PLoS paper for mention of the Red Queen. Guess what - not a dicky bird. The paper seems (on first read) to be a competent comparative analysis of wing-loading and flying speed across a range of different birds, hence the Author's Summary:
"Analysing the variation in flight speed among bird species is important in understanding flight. We tested if the cruising speed of
different migrating bird species in flapping flight scales with body mass and wing loading according to predictions from aerodynamic
theory and to what extent phylogeny provides an additional explanation for variation in speed. Flight speeds were measured
by tracking radar for bird species ranging in size from 0.01 kg (small passerines) to 10 kg (swans). Equivalent airspeeds of 138 species
ranged between 8 and 23 m/s and did not scale as steeply in relation to mass and wing loading as predicted. This suggests that
there are evolutionary restrictions to the range of flight speeds that birds obtain, which counteract too slow and too fast speeds among
bird species with low and high wing loading, respectively. In addition to the effects of body size and wing morphology on flight
speed, we also show that phylogeny accounted for an important part of the remaining speed variation between species. Differences
in flight apparatus and behaviour among species of different evolutionary origin, and with different ecology and flight styles, are
likely to influence cruising flight performance in important ways."


The closing paragraph of the main section of the paper seems to be as close as the authors get to discussing the broader context for their findings:
"We suggest that functional differences in flight apparatus and musculature among birds of different life and flight styles (differences often associated with evolutionary origin) have a significant influence on the birds' performance and speed in sustained cruising flight. Thus, our results strongly indicate that there is a diversity of cruising flight characteristics among different types of birds over and above the general scaling effects of mass and wing loading that remains to be investigated and understood, aerodynamically [30 <http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050197#journal-pbio-0050197-b030>], kinematically [26 <http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050197#journal-pbio-0050197-b026>,31 <http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050197#journal-pbio-0050197-b031>], physiologically [22 <http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050197#journal-pbio-0050197-b022>], as well as ecologically [2 <http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050197#journal-pbio-0050197-b002>,10 <http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050197#journal-pbio-0050197-b010>]."


Well, nothing too contentious there. I've wondered for a while as to whether the Red Queen hypothesis is relevant to vertebrate palaeontology - does it make any predictions that are testable using fossil data? And I see no obvious reason to pull out the Red Queen to explain the original paper's findings over, say, Sewell Wright's adaptive peaks. But now I'm even more curious as to how the (Swedish based) authors of this paper feel about their work being used by a US colleague to push a particular line on macroevolutionary processes. Are they comfortable with their work being represented in the English language science press in this way?


-- ***************** Colin McHenry School of Environmental and Life Sciences (Geology) University of Newcastle Callaghan NSW 2308 Australia Tel: +61 2 4921 5404 Fax: + 61 2 4921 6925

******************