Gleaning bats that can detect motionless prey still prefer moving katydids

New paper: Geipel* I, Kernan* CE, Litterer AS, Carter GG, Page RA, ter Hofstede HM. 2020. Predation risks of signalling and searching: bats prefer katydids in motion in Biology Letters.

When I was a kid, I would throw tiny pebbles or bits of wood in the air when bats were foraging, and the bats would often dive at them. In one memorable case, much to my delight, the bat actually caught and then dropped a stick! This observation gave me the wrong impression that bat sonar must not be that great, but later I read about bats identifying moth species by the fluttering wingbeat [1]. The performance of bat echolocation differs a lot between species and context.

For example, the task of prey detection differs between grabbing a moth from the open air (aerial hawking) and picking an insect off a leaf in a cluttered environment (gleaning). Many gleaning bats find their prey by eavesdropping on prey sounds like mating calls, but some echolocating gleaners can still find insects sitting silently and motionless on a leaf. Inga Geipel has led a series of studies to both demonstrate this surprising ability [2] and to understand how the bats do it [3]. The bat she has often studied, Micronycteris microtis, could even tell the difference between a dead dragonfly and a replicate dummy, but they first get close enough to inspect from the right angle (see videos below). Inga loves these amazing bats, maybe even more than I like vampire bats.

Inga Geipel

At the Smithsonian Tropical Research Institute (STRI), there is a tradition of great things happening when two researchers each focusing on the perspective of a different species come to together to better understand how those two species interact through predation, parasitism, or mutualism. For example, excellent work has been done on tungara frog calls and how they are exploited by predatory bats [4], parasitic midges [5], and how such interactions affects the evolution of the frog calls [6]. Often this work is pursued by a team looking at the interaction from different points of view.

In a similar vein, Inga collaborated with PhD student Ciara Kernan and STRI Intern Amber Litterer who were interested in studying how predatory bats shape katydid communication. We know there is greater predation risk for males signalling to females, but what about other aspects of katydid courtship? The male katydids they studied produce mating calls, but both males and females also signal to each other with vibrations (called tremulations) and they also walk towards each other. Does this increased movement increase predation risk?

With guidance from Inga, Ciara and Amber conducted experiments that revealed that the movements of mate searching can incur risk too. They tested the choices of Inga’s beloved Micronycteris microtis,  and found that, although these bats don’t need motion to find their prey, they still detect and preferred to investigate moving targets. This finding might explain why bats still often eat female katydids that do not call.

Amber and Ciara

Inga and Ciara were co-first authors. I also helped with data analysis. This work was supervised by Smithsonian Staff Scientist Rachel Page and Dartmouth Assistant Professor Hannah tef Hofstede, two labs working at the intersection of evolution and sensory ecology, which is I think one of the most fun and exciting fields!

This artwork is by Amy Koehler an artist and illustrator from San Francisco, California. She is a graduate of CSUMB’s Science Illustration Program and currently the artist-in-residence at the Page Bat Lab at STRI. She hopes to make science approachable through illustration and to inspire others to be more engaged in the world around them.

References

  1. von der Emde, G., & Schnitzler, H. U. (1990). Classification of insects by echolocating greater horseshoe bats. Journal of Comparative Physiology A, 167(3), 423-430.
  2. Geipel, I., Jung, K., & Kalko, E. K. (2013). Perception of silent and motionless prey on vegetation by echolocation in the gleaning bat Micronycteris microtis. Proceedings of the Royal Society B: Biological Sciences, 280(1754), 20122830.
  3. Geipel, Inga, Jan Steckel, Marco Tschapka, Dieter Vanderelst, Hans-Ulrich Schnitzler, Elisabeth KV Kalko, Herbert Peremans, and Ralph Simon. “Bats actively use leaves as specular reflectors to detect acoustically camouflaged prey.” Current Biology 29, no. 16 (2019): 2731-2736.
  4. Tuttle, M. D., & Ryan, M. J. (1981). Bat predation and the evolution of frog vocalizations in the Neotropics. Science, 214(4521), 677-678.
  5. Bernal, X. E., Rand, A. S., & Ryan, M. J. (2006). Acoustic preferences and localization performance of blood-sucking flies (Corethrella Coquillett) to túngara frog calls. Behavioral Ecology, 17(5), 709-715.
  6. Akre, K. L., Farris, H. E., Lea, A. M., Page, R. A., & Ryan, M. J. (2011). Signal perception in frogs and bats and the evolution of mating signals. Science, 333(6043), 751-752.

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