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Re: Great in the air, not so good underwater
Size in terms of body mass, or size in terms of wing area? My hunch
(without having access to more information) is that the authors were
referring to mass. If so, that would imply that the Guillmots and
razorbills have larger wings than penguins of similar mass. If so, it
is to be expected that when swimming, they would stroke at a lower
frequency than penguins, due to the additional loading on their
relatively larger wings.
I also suspect that is what they mean, though I'll have to go grab the
actual paper to confirm. One thing I do find odd in that summary is
that the mass overlap between penguins and alcids is rather minimal;
the guillemots in my dataset range from 906 grams to 1177 grams.
They're among the largest alcids; razorbills are only slightly larger.
The smallest penguins, on the other hand, fall at about 1.3 kg.
On Wednesday, December 6, 2006, at 09:26 PM, Dann Pigdon wrote:
Marine animals may trade off their swimming efficiency against flying
ability, according to a novel study in which motion sensors were
attached to wild seabirds, whales and penguins to reveal how they move
Using "marine animals" here is a bit odd in terms of wording; the only
vertebrate amphibious flyers are birds. Most of them are alcids, with
a few shearwaters, dippers, etc. in there as well. So really, the only
living "tradeoff" examples are avian.
[Katsufumi] Sato’s team [University of Tokyo] found that the
size-to-flap ratio does not apply to seabirds. Guillemots and
razorbills use their wings for both flying and swimming, and
underwater they stroke at a lower frequency than other seabirds of a
similar size, such as penguins, suggesting inefficiency for their
Again, wording seems a bit odd. I will have to get the paper tonight,
but it seems like penguins are just about the only "other seabirds"
that they could be using for the comparison, unless they got data from
shearwaters as well (the only other avian aquaflyers in the same body
size range as alcids).
... this study suggests that the different wing shapes and flight
styles that are optimal for either air or water are very different.
Increasingly efficient adaptations for an underwater flier tend to
move away from aerial flight.
That has been the traditional view on amphibious flyers (and the
transition to full aquatic lifestyles from flying ancestors, as in
penguins). There is probably some distinct truth in it, but the
situation is likely to be a bit more complicated than it seems. Alcids
have poor maneuverability, but they are very fast flyers. They are
also very good swimmers, really, as penguins set a high bar (and thus
being less efficient than a penguin is not immediately "poor").
Penguins may be more efficient swimmers for a number of reasons. One
factor is absolute size: a number of parameters related to efficiency
are easier to maximize at sizes above those reached by the largest
alcids. Generally speaking, aquaflying efficiency in birds will favor
relatively large size, small wings with moderately high aspect ratios
(see Lovvorn's work), and an active power upstroke (see Lovvorn, Sato
et al.'s previous studies, and the classic Clark and Bemis paper). The
power upstroke is important not only for the obvious benefit of
generating more thrust per wing oscillation cycle, but also because net
drag decreases if the body speed stays high on the upstroke. To quote
Lovvorn (2001) in regards to murres: "When fuselage speed was
relatively higher during upstrokes, lower net drag at the same mean
speed increased the ability to glide between strokes, thereby
decreasing the cost of swimming."
These factors tend to mean high wing loadings and large
supracoracoideus mass. Both of these are good up to a point for aerial
flying *if* the animal is a rapid, lower maneuverability species (like
alcids). As such, I'm not sure if alcids are making as much of a
tradeoff as it appears at first glance. That said, there is still some
tradeoff, because alcids cannot manage the most efficient body mass,
wing loading, and relative supracora. mass relationships and stay
volant (hence the loss of volancy in at least two alcid lineages, and
the loss of volancy in penguins).
Interestingly, penguins rank as the most efficient fully homeothermic
swimmers. I cannot remember the proper reference for that bit of
information right off the top of my head, but I have a copy of the
paper stored away here and I'll send the citation along to this thread
when I dig it out. I believe efficiency was measured as mass-specific
fuel consumption per unit distance.