Bats use leaves as mirrors to find prey in the dark

August 01, 2019

On moonless nights in a tropical forest, bats slice through the inky darkness, snatching up insects resting silently on leaves--a seemingly impossible feat. New experiments at the Smithsonian Tropical Research Institute (STRI) show that by changing their approach angle, the echolocating leaf-nosed bats can use this sixth sense to find acoustically camouflaged prey. These new findings, published in Current Biology, have exciting implications for the evolution of predator-prey interactions.

"For many years it was thought to be a sensory impossibility for bats to find silent, motionless prey resting on leaves by echolocation alone," said Inga Geipel, Tupper Postdoctoral Fellow at STRI. Geipel's team discovered how the bats achieve the impossible. By combining evidence from experiments using a biosonar device to create and measure artificial signals, with evidence from high-speed video observations of bats as they approach prey, the importance of the approach angle was revealed.

Bats have a superpower humans do not share: they flood an area with sound waves and then use information from the returning echoes to navigate through the environment. Leaves reflect echolocation signals strongly, masking the weaker echoes from resting insects. So in the thick foliage of a tropical forest, echoes from the leaves may act as a natural cloaking mechanism for the insects, known as acoustic camouflage.

To understand how bats overcome acoustic camouflage and seize their prey, the researchers aimed sound waves at a leaf with and without an insect from more than 500 positions in order to create a full, three-dimensional representation of the echoes. At each position, they calculated the intensity of the echoes for five different frequencies of sound that represent the frequencies of a bat's call.

Leaves both with and without insects strongly reflect back the sound if it comes from straight ahead (i.e., from angles smaller than 30 degrees). When a bat approaches from these angles, it cannot find its prey as strong echoes from the leaves mask the echoes from the insect. But Geipel and colleagues found that if the sound originates from oblique angles greater than 30 degrees, the sound is reflected away from the source and leaves act like a mirror, just as a lake reflects the surrounding forest at dusk or dawn. The approach angle makes a resting insect detectable.

Based on these experiments, Geipel and colleagues predicted that bats should approach resting insects on leaves from angles between 42 and 78 degrees, the optimal angles for discerning whether a leaf has an insect on it or not.

Next, Geipel recorded actual bats at STRI's Barro Colorado Island research station in Panama as they approached insects positioned on artificial leaves. Using recordings from two high-speed cameras, she reconstructed the three-dimensional flight paths of the bats as they approached their prey and determined their positions. She discovered that, as predicted, almost 80 percent of the approach angles were within the range of angles that makes it possible for the bats to distinguish insect from leaf.

"This study changes our understanding of the potential uses of echolocation," Geipel said. "It has important implications for the study of predator-prey interactions and for the fields of sensory ecology and evolution."
-end-
Author affiliations include STRI, the University of Antwerp, University of Ulm, University of Cincinnati, University of Tübingen and Vrije Universiteit Amsterdam.

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a unit of the Smithsonian Institution. The Institute furthers the understanding of tropical biodiversity and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystems. Promo video.

Geipel, I., Steckel, J., Tschapka, M., et al. 2019. Bats actively use leaves as specular reflectors to detect acoustically camouflaged prey. Current Biology. https://doi.org/10.1016/j.cub.2019.06.076

Smithsonian Tropical Research Institute

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.