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Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)





With regards to the gliding issue: there are quite a few living flying animals that virtually never glide. However, even basic calculations will demonstrate that most of these species can glide if need be - they simply do not for reasons of efficiency and gait. Some of the hummingbirds may be pretty close to the range where gliding is effectively not usable, but hummingbirds are so extreme that general rules should not be attached to them (even then, most species can probably glide for a brief moment).


Better examples of continuous flapping morphs, from the perspective of the current discussion, include things like anseriforms and loons. In these cases, the planform and aerobic capacity make gliding a poor option relative to continuous flapping, but that doesn't make gliding impossible - they just don't gain much from gaits that utilize unpowered phases. For example, using some averaged data from wild- caught common loons, I calculate a min sink of 1.08 m/s and a glide ratio of about 15. That's a pretty high min sink, and the circle radius is huge, too (so a loon isn't going to be thermal soaring any time soon), but clearly the animal could glide if it wanted. In fact, there is often a glide phase in heavily loaded, continuous flapping seabirds just prior to the landing phase.

And yes, pteropodid bats can soar effectively in thermals, but they rarely do so - probably for ecological reasons more than anything else. They're not particularly good at soaring over distance (very low glide speed, for one thing), but the low span loading generates a small minimum sink rate, and the average turning radius of a large fruit bat is more than sufficient for staying in even very small thermals. Part of the problem for large bats is that they cannot manage the same sort of span reduction as birds, meaning that the wing loading cannot be greatly increased for travel between lifting sources (as it would be by a soaring vulture, for example), and thus the max rate of soaring travel is quite low. Molossids should have decent enough glide ratios, but their small size and physiology keeps them in a more or less continuous flapping bracket. In a nutshell: there are no living bats that are particularly well adapted to extended soaring flight, but the larger species can manage it here and there.

Cheers,

--Mike



Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280-0181
habib@jhmi.edu