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

[Mike Habib <habib@jhmi.edu>]

>

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