Re: Birds ignore physics to fly in 3rd gear

[Colin McHenry <cmchenry@westserv.net.au>]

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?


--
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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

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