Monday, April 9, 2012

Bounding Bats

There is a wicked paper out in PLoS ONE on how bats can actually use their uropatagia and tails to get a little extra lift during slow flight and launch.  The paper is freely available (like all PLoS papers) here.

Adams et al. (2012) show some really neat dynamics for the uropatagium and tail in bats.  They also just get some great shots of bat launch in fringed myotis.  What's particularly interesting here is that previous work on ground launch in bats has focused on the species with the most powerful takeoffs: vampire bats and New Zealand short tailed bats.  Those models have been very informative, and I have studied the experimental data on vampire bats (Desmodus) extensively in my reconstructions of pterosaur launch.  However, most bats are not built like vampires.  The genus Myotis is a large group of rather "typical" bats: while the genus is hardly uniform, it is essentially comprised of small, insectivorous species that rarely come to the ground.

On the whole, the launch in Myotis works about the same as in Desmodus, but I do note one really neat difference: if you take a look at the figure I've pasted here from Adams et al. (2012), you'll note that in the first panel (bottom) the bat is pushing off at the wrist followed by the wing fingers.  It's actually unfurling the wing part of the way early on (instead of late, as in Desmodus) and letting the highly compliant fingers in the wing bend to produce a pushing surface.  That's not just bending at a joint, mind you, that's the actual bone that's flexing.  Spectacular stuff.

This is not the first time that bat tails have been implicated in flight control.  Another paper, also in PLoS ONE predicted the role of the tail in flight control previously (Gardiner et al., 2011).  It's a nice little theoretical paper and it is neat that a theory-based work and an experimental one on the same bit of morphology hit in back-to-back years.

If you want to check out what the vampire version of bat launch, you can turn your cursors here for the manuscript in the Journal of Experimental Biology (Schutt et al., 1997).  You can also check out a video of a vampire bat running here.

Adams RA , Snode ER , Shaw JB (2012) Flapping Tail Membrane in Bats Produces Potentially Important Thrust during Horizontal Takeoffs and Very Slow Flight. PLoS ONE 7(2): e32074. doi:10.1371/journal.pone.0032074

Gardiner JD, Dimitriadis G, Codd JR, Nudds RL (2011) A Potential Role for Bat Tail Membranes in Flight Control. PLoS ONE 6(3): e18214. doi:10.1371/journal.pone.0018214

Schutt, W. A. Jr., Altenbach, J. S., Young, H. C., Cullinane, D. M., Hermanson, J. W., Muradli, F., and Bertram, J. E. A. 1997. The dynamics of flight-initiating jumps in the common vampire bat Desmodus rotundus. The Journal of Experimental Biology, 200, 3003-3012.


  1. The illustration in the paper makes it seem like a particularly vigorous butterfly stroke, with a strong kick to finish it off. Very cool!

    The finger bone spring is your observation, right? (I didn't find it mentioned in the paper.)

  2. Yes, the finger bone loading is my own observation; it's not something the authors were looking at. Compliance of the fingers in bats (specifically those encased in the wing - i.e. digits 2-5) has been well studied and described previously by individuals like Sharon Swartz and Kevin Middleton.

  3. Compliance means spring-action bending, correct?
    I seriously have to get around to animating a pterosaur jump launch, or from water.

  4. Compliance means that it's "bendy": that is, you can flex it and it will deform, rather than snap. Some compliant materials spring back, as you allude to, while others will keep the new shape. So, for example, bone is "springy", as are tendons, etc., but a steel wire is compliant but does not typically spring back to shape - it is compliant, but not particularly elastic.

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