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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 underwater...

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 size...

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.