Nav: Home

Echolocation: Making the best of sparse information

May 20, 2019

New findings reported by Ludwig-Maximilians-Universitaet (LMU) in Munich researchers challenge a generally accepted model of echolocation in bats. They demonstrate that bats require far less spatial information than previously thought to navigate effectively.

Bats find their way in the dark by emitting ultrasonic signals and analyzing the echoes generated when these signals impinge on, and are reflected by, objects in their environment. Experiments carried out by LMU researchers now refute a central postulate of the conventional model of echolocation. "Up to now, it has been assumed that the echoes provide a kind of acoustic image of the environment, which allows bats not only to detect objects but also to perceive the gaps between them. This notion turns out to be wrong. Our experiments show that bats have very little ability to spatially resolve objects. Their navigational system makes do with a surprisingly small amount of spatial information, and its mode of operation differs fundamentally from our conventional picture of echolocation," says Lutz Wiegrebe, a professor in the Neurobiology Division. The new findings appear in the latest issue of the journal Current Biology.

In their study, Wiegrebe and colleagues used bats that had been trained to emit ultrasonic signals when they detected the acoustic reflections of objects in their environment. In the experimental set-up, the bats emitted signals which were reflected from a target placed directly in front of them, but were also exposed to reflections originating from sources to the left and right of the target of interest. The latter therefore served as cluttering targets which were displaced from the target of interest by angular distances that were varied from experiment to experiment. "The bats were extremely irritated by the virtual reflections, and were able to detect the target of interest only when the virtual targets were placed relatively far away from it."

This paradigm used to measure the spatial resolution of the bat echolocation system is analogous to that used to measure the spatial resolution of the visual system. In the mammalian retina, the anatomical organization of the photoreceptor cells itself provides the basis for high spatial resolution. "But echolocation works in an entirely different way," Wiegrebe explains. "The sensory cells in the inner ear do not encode axes in space, they encode time and frequency. Spatial information must be secondarily derived from these inputs by neuronal processing. Our experiments demonstrate that the spatial resolution of the bat echolocation system is approximately three orders of magnitude worse than that of the human visual system. In other words, bats navigating by echolocation receive an extremely fuzzy picture of their environment. A visually simple task like 'how many fingers am I holding up' is extremely difficult to solve with biosonar. Nevertheless, bats can navigate very effectively." The authors of the new study believe that the animals compensate for the deficit in spatial resolution by constantly updating the incoming information relating to the distance and direction of objects, and concentrating on determining the relative positions of the objects that are closest to them.

The results may well have implications for manmade navigation systems. "The navigational systems used in e.g. autonomous vehicles use a camera to capture a continuous stream of information. It is conceivable that much of this information is redundant. Bats use a much simpler scheme that does not depend on the acquisition of a 3-D image of their environment, such as that provided by the visual system. Yet they can navigate quite effectively."

In a paper recently published in the journal iScience, Leonie Baier (a member of Lutz Wiegrebe's research group) and Dr. Holger Goerlitz of the Max Planck Institute for Ornithology showed that some bat species are preferentially sensitive to surface-wave patterns with high spatial frequencies, which allows them to gauge depth, i.e. differentiate between foreground and background. This ability enables them to detect an insect on the surface of a pond, for instance. "Our work has now shown that bats cannot resolve this information spatially," says Wiegrebe. If the water surface is covered with vegetation, a foraging bat can no longer localize the insect.

Ludwig-Maximilians-Universität München

Related Bats Articles:

Tiny insects become 'visible' to bats when they swarm
Small insects that would normally be undetectable to bats using echolocation suddenly become detectable when they occur in large swarms.
Illumination drives bats out of caves
Researchers of the Leibniz Institute for Zoo and Wildlife Research and the Max Planck Institute for Ornithology have investigated how the illumination of bat caves affects the animals' behaviour and whether the colour of light makes a difference on their flight.
Bats may benefit from wildfire
Bats face many threats -- from habitat loss and climate change to emerging diseases, such as white-nose syndrome.
Ecology: Wildfire may benefit forest bats
Bats respond to wildfires in the Sierra Nevada Mountains in varied but often positive ways, a study in Scientific Reports suggests.
Saving bats from wind turbine death
Wind energy holds great promise as a source of renewable energy, but some have wondered addressing climate change has taken precedence over conservation of biodiversity.
Bats in attics might be necessary for conservation
Researchers investigate and describe the conservation importance of buildings relative to natural, alternative roosts for little brown bats in Yellowstone National Park.
Vampire bats give a little help to their 'friends'
Vampire bats could be said to be sort of like people -- not because of their blood-sucking ways, but because they help their neighbors in need even if it's of no obvious benefit to them.
How bats relocate in response to tree loss
Identifying how groups of animals select where to live is important for understanding social dynamics and for management and conservation.
Bats use private and social information as they hunt
As some of the most savvy and sophisticated predators out there, bats eavesdrop on their prey and even on other bats to collect a wide variety of information as they hunt.
There are way more species of horseshoe bats than scientists thought
Horseshoe bats are bizarre-looking animals with giant ears and elaborate flaps of skin on their noses that they use like satellite dishes.
More Bats News and Bats Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

There's so much we've yet to explore–from outer space to the deep ocean to our own brains. This hour, Manoush goes on a journey through those uncharted places, led by TED Science Curator David Biello.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Dispatch 2: Every Day is Ignaz Semmelweis Day
It began with a tweet: "EVERY DAY IS IGNAZ SEMMELWEIS DAY." Carl Zimmer – tweet author, acclaimed science writer and friend of the show – tells the story of a mysterious, deadly illness that struck 19th century Vienna, and the ill-fated hero who uncovered its cure ... and gave us our best weapon (so far) against the current global pandemic. This episode was reported and produced with help from Bethel Habte and Latif Nasser. Support Radiolab today at