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Re: Pterosaur wing membranes



I remember seeing film of fuit bats soaring and I've just bumped into a ref
about soaring flight in a "Flying Fox", a fruit bat. The site says, "It flies
with a slow wing-beat, frequently glides and can also soar on thermals."


http://www.animalinfo.org/species/bat/pterlivi.htm

Here's a photo: http://ibis.nott.ac.uk/Action-Comores/batflight2.jpg


I suspect you're referring to the Thomson (2002) paper on soaring in flying foxes, which I also find interesting. However, the situation is very different from in pterosaurs. Flying foxes, when they soar (and it's not that widespread, it would seem) are convective soarers (as the site says, referencing thermal utilization). Low wing loadings are quite nice for convective soaring, which is why vultures have low wing loadings. However, low wing loadings are terrible for dynamic soaring (which is why albatrosses have high wing loadings). Pterosaurs were pretty obviously built for dynamic soaring (with incredibly high aspect ratios, for starters).

Bats are, in fact, not very good at gliding, all told. Most cannot glide much at all, and the flying foxes glide very slowly. At higher wing loadings, an animal glides faster (getting from point A to point B more quickly), without having to use more energy. The amount of vertical travel remains unchanged, they just get to where they're going faster. That doesn't mean gliding is no good to large bats; they obviously use it when appropriate and it saves energy. Vultures also glide pretty frequently. But, all told, they're not good at covering distance or riding shears. Rather, such low-loading animals are good at loitering.

Pterosaurs, by contrast, were great at gliding and dynamic soaring, but probably pretty poor at loitering (compared to a vulture, that is, which is a very high bar).

Cheers,

--Mike Habib