Research Article

Scaling of Soaring Seabirds and Implications for Flight Abilities of Giant Pterosaurs

  • Katsufumi Sato mail,

    Affiliation: International Coastal Research Center, Ocean Research Institute, The University of Tokyo, Otsuchi, Iwate, Japan

  • Kentaro Q. Sakamoto,

    Affiliation: Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan

  • Yutaka Watanuki,

    Affiliation: Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Japan

  • Akinori Takahashi,

    Affiliation: National Institute of Polar Research, Itabashi, Tokyo, Japan

  • Nobuhiro Katsumata,

    Affiliation: International Coastal Research Center, Ocean Research Institute, The University of Tokyo, Otsuchi, Iwate, Japan

  • Charles-André Bost,

    Affiliation: Centre d'Etudes Biologiques de Chizé-CNRS, Villier en Bois, Beauvoir/Niort, France

  • Henri Weimerskirch

    Affiliation: Centre d'Etudes Biologiques de Chizé-CNRS, Villier en Bois, Beauvoir/Niort, France

  • Published: April 29, 2009
  • DOI: 10.1371/journal.pone.0005400
  • Published in PLOS ONE

Reader Comments (4)

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Application of Avian Scaling to Pterosaurs

Posted by MHabib on 04 May 2009 at 18:03 GMT

I applaud the empirical approach, and the generation of some very useful data, but I feel that there are a few notable problems plaguing the conclusions and use of the results. They do not invalidate the analysis, just some of the conclusions.

The first issue is the assumption that a global maximum exists for size in flying animals. The authors start by using such an assumption, then relax it a bit later in the discussion. However, they implicitly keep such an assumption by indicating that the scaling curves they generated should apply to animals far outside the morphology and phylogenetic bracket of their sample. What the authors probably have is the maximum size for a procellariiform seabird - not the maximum size for a soaring animal, or even the maximum size for a coastal soaring animal. The authors state that:

"Some studies have proposed that large pterosaurs such as Pteranodon and Quetzalcoatlus may have had narrow wings similar to those of albatrosses, and used slope soaring and dynamic soaring [18]. However, our study of living Procellariiformes as model animals suggests that if pterosaurs larger than 41 kg (or 5.1-m wingspan) had the narrow wings, they could not have attained sustainable flight in environments similar to the present."

There seems to be a bit of confusion here, as the authors have apparently assumed that their calculated scaling patterns should hold for a given aspect ratio regime. Flapping limits also vary according to relative muscle mass, launch type, wing efficiency, etc. As such, the reconstructed AR has little to do with the problem at hand. I also find it strange that the authors consider their paper support for Darren and Mark's bit on semi-terrestrial hunting in azhdarchids. Darren and Mark put together a fine paper, don't get me wrong, but poor launching ability and the inability to fly without external lifting conditions would argue *against* such a mode of life, as the animals would be stuck on the ground after feeding. Semi-terrestrial predators need a strong ability to launch and gain altitude, at least for bursts.

The other major issue, in my mind, comes from the assumptions regarding launch. Still, after all the years and fine work that have gone into launch mechanics (Tobalske, Earls, Rayner, etc), we have biologists that are confused about how launch works in birds at a general level. The authors suggest that:

"Takeoff is the transition from being supported by something that is essentially part of the earth's surface to being supported entirely by aerodynamic forces in flight, and these depend on air flowing over the wings [7]. Takeoff seems to be the most crucial task for flying birds and requires more active flapping than level flight because the flight speed is zero at the beginning and the birds must raise their body mainly by muscular effort."

This is, technically speaking, true. However, further reading indicates that the "muscular effort" indicated is meant to be rapid flapping - but most of the launch impulse comes from the hindlimbs. I have to admit that I feel a bit like a broken record on this one these days - birds do not flap themselves into the air, for precisely the reasons indicated in the paper (ironically enough): at low flow speeds, there is limited fluid force. Thus, speed needs to be generated *first*, then the wings can engage to good effect (at small sizes, the clearance from the ground is more important - as size increases, the velocity component of the hindlimb impulse increases).

Overall take home message (in my opinion, anyway): Nice data, neat analysis, with a possible limit for procellariiform body size. The application to pterosaur limits is, however, not as strong.

No competing interests declared.