A new social role for echolocation in bats that hunt together

Date: June 19, 2020

Source: Smithsonian Tropical Research Institute

Searching for food at night can be tricky. To find prey in the dark, bats use echolocation, their "sixth sense." But to find food faster, some species, like Molossus molossus, may search within hearing distance of their echolocating group members, sharing information about where food patches are located. Social information encoded in their echolocation calls may facilitate this foraging strategy, according to a recent study by Smithsonian Tropical Research Institute (STRI) scientists and collaborating institutions published online in Behavioral Ecology.

Previous research has identified several ways in which echolocation can transfer social information in bats. For example, "feeding buzzes," the echolocation calls bats produce to home in on prey they've spotted, can serve as cues of prey presence to nearby eavesdropping bats. On the other hand, echolocation calls that bats produce while looking for food, called "search-phase" calls, were not known to transfer social information.

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Echolocation found to be cheap for deep-diving whales

NOVEMBER 1, 2019

by University of St Andrews

A new international study led by Aarhus University in Denmark, in collaboration with the Universities of St Andrews and La Laguna, Tenerife, reveals how whales have evolved to live in the world's deepest oceans.

Many whales and dolphins, including the champion deep-diving beaked whales, use echolocation, the ability to locate objects by reflected sound, to find food in the dark of the deep ocean. Scientists have not been able to agree on how much energy this remarkable sensing ability takes, until now.

A new study published today (Thursday 31 October) in the journal Scientific Reports reveals that, at least for short-finned pilot whales, echolocation is cheap. This may help explain how echolocating whales evolved to live in deep waters throughout the world.

In a throwback to terrestrial ancestors, whales use air to make their intense echolocation click sounds and this raises a problem for deep divers. Air compresses with depth so that at 700m deep, where pilot whales hunt, a lung-full of air has shrunk to 1.5% of its volume. But the new study shows that pilot whales use tiny amounts of air to make each click so this volume goes a long way. Even so, whales need to capture the air used by each click and recycle it, like a SCUBA rebreather, to be able to echolocate throughout their dives.

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A bigger nose, a bigger bang: Size matters for ecoholocating toothed whales

Whales, dolphins, and porpoises have all evolved to use similar narrow beams of high intensity sound to echolocate prey

Date:  November 15, 2018

Source:  Aarhus University

Trying to find your lunch in the dark using a narrow flashlight to illuminate one place at a time may not seem like the most efficient way of foraging. However, if you replace light with sound, this seems to be exactly how the largest toothed predators on the planet find their food. A paper out this week in the journal Current Biology shows that whales, dolphins, and porpoises have all evolved to use similar narrow beams of high intensity sound to echolocate prey. Far from being inefficient, this highly focused sense may have helped them succeed as top predators in the world's oceans.

A new sense enabled toothed whales to succeed in diverse habitats

32 million years ago, the ancestors of toothed whales and baleen whales diverged as the ancestors of toothed whales -- including dolphins, porpoises and sperm whales -- evolved the ability to echolocate; to send out sound pulses and listen for the returning echoes from objects and prey in their environment. This new sense allowed these animals to navigate and find food in dark or murky waters, during the night, or at extreme depths. Since then, this evolutionary step has allowed these animals to occupy an amazing diversity of habitats, from shallow freshwater rivers to the great ocean deeps.

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Fruit bat's echolocation may work like sophisticated surveillance sonar

February 7, 2018 by Hannah Hickey, University of Washington

New research from the University of Washington suggests that the Egyptian fruit bat is using similar techniques to those preferred by modern-day military and civil surveillance. The results could inspire new directions for driverless cars and drones.

The new open-access paper in PLoS Biology shows how the animals are able to navigate using a different system from other bats.

"Before people thought that this bat was not really good at echolocation, and just made these simple clicks," said lead author Wu-Jung Lee, a researcher at the UW's Applied Physics Laboratory. "But this bat species is actually very special—it may be using a similar technique that engineers have perfected for sensing remotely."

While most other bats emit high-pitched squeals, the fruit bat simply clicks its tongue and produces signals that are more like dolphin clicks than other bats' calls. Fruit bats can also see quite well, and the animals switch and combine sensory modes between bright and dark environments.

An earlier study showed that Egyptian fruit bats send clicks in different directions without moving their head or mouth, and suggested that the animals can perform echolocation, the form of navigation that uses sound, better than previously suspected.

"But no one knew how they do it, and that's when I got excited, because there's something going on that we don't understand," Lee said.

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Bats avoid collisions by calling less in a crowd

Date:  January 3, 2017
Source:  Society for Integrative and Comparative Biology (SICB)

In the warm summer months, bats go about their business each night, flying and gobbling up insects (a benefit to us). Using echolocation (making calls and listening for returning echoes to figure out where objects are) they can hunt and navigate around obstacles in total darkness, often in large groups. But if everybody is echolocating at once, how do bats pick out their own echoes?

This question has mystified scientists since the discovery of echolocation, but Dr. Amanda Adams and Dr. Michael Smotherman at Texas A&M University may have found part of the answer. Using wild-caught Mexican free-tailed bats, they study whether the bats adjust their echolocation calls in response to other bat calls.

When bats are flying in a cluttered environment they increase their call rates and listen for returning echoes. This gives them a detailed idea of the location of objects or even other bats. But if a bat's echo overlaps with another bat's call or echo, the information gets lost. This is "interference," and it can be a real problem for a bat because losing information could cause it to miss the insect it was trying to eat or even run into something.

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What role does mouth shape play for echolocating bats?

Specialized facial muscles support sonar beam forming by free-tailed bats

 

Date: November 28, 2016

Source: Acoustical Society of America (ASA)

Echolocating bats are able to manipulate the acoustic projection pattern of their sonar pulse emissions -- but how they do it remains a largely unexplored mystery.

The Mexican free-tailed bat, Tadarida brasiliensis, appears to do it by adjusting the shape of its mouth cavity, aka beam forming, similar to the way humans purse their lips to create an "O" sound. While this is usual for humans, it is unusual for animals. Flying Tadarida lift their nose and lips before each echolocation pulse with a set of specialized facial muscles.

In a moment of serendipity while working on another project, Samantha Trent, a doctoral candidate working with Michael Smotherman at the Texas A&M Institute for Neuroscience, noticed a large group of muscles running straight down the middle of the top of the bat's skull. A set of muscles like this is quite unusual in size and location for a small mammal, so she questioned their purpose.

During the 172nd Meeting of the Acoustical Society of America and the 5th Joint Meeting with Acoustical Society of Japan, being held Nov. 28-Dec. 2, 2016, in Honolulu, Hawaii, Smotherman will present his work with Trent exploring the muscle's complex activity patterns during sonar performance, whether the muscle tissue displays necessary fast-twitch specializations to accommodate echolocation, and how manipulations of mouth shape altered 3-D beam patterns.

"It seems evident that this particular set of muscles is involved in changing the shape of the bat's mouth -- especially during echolocation," Trent said. "We think this aids the bat's ability to change the shape of its outgoing echolocation pulse beam."

To put this to the test, they used a microphone array to capture recordings from all around the bat's head to build a picture of the beam shape of sound coming out its mouth. They also recorded electrical activity from these muscles while the bats were freely echolocating to determine how these muscles are involved in producing echolocation pulse streams.

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Frog-hunting bats have ‘cocktail party effect’ workaround In noisy environment, hunters shift from listening for croaks to using echolocation – via Herp Digest

Science News by Susan Milius, Science News 9/15/16

Humankind is loud, and research already suggests that birds alter their singing in urban noise. Now tests show that bats listening for the frogs they hunt switch from mostly quiet eavesdropping to pinging echolocating when artificial sounds mask the frog calls. That way, the bats can detect the motion of the frogs’ vocal sac poofing out with each call, researchers report in the Sept. 16 Science.

That switch in sensory tactics could make bats the only animals besides people shown to react this way to interfering din in the classic cocktail party scenario, says study coauthor Wouter Halfwerk of Vrije University Amsterdam. People straining to hear each other over the cacophony of a party can get a boost in communication by paying attention to each other’s mouth movements. He points out that watching someone’s lips lets people tolerate about an extra 20 decibels of tipsy shrieking and shouting.

Conservation biologists worry about the effects of human racket on other residents of the planet. Other researchers, for instance, found that noise interfered with pallid bats’ success in hunting insects on the wing. The fringe-lipped bats (Trachops cirrhosus) in the new study, however, specialize in frogs instead of insects. Hungry bats listen to frog choruses and swoop out of the darkness to carry off a male chirping his advertisements for a mate. “A talking pickle” is what Halfwerk calls the frog.

Researchers tested 12 wild-caught bats in outdoor flight cages in Panama. Bats perching (upside down, of course) in cages were perfectly willing to make a grab at robotic frogs deployed in the cages. The robofrogs, modeled by an artist on the túngara species the bats naturally hunt, sit motionless but can on command start inflating a specially constructed balloon in time with broadcast calls.

In this setup, interfering noise changed normal hunting. When researchers broadcast sounds that partially masked the main frequency of telltale frog calls, bats waited longer than normal to strike and also strongly preferred pouncing on a robofrog that was inflating his sac instead of an identical frog squatting nearby with a deflated sac. Recordings of bat noises from the perch showed that the hunters were pinging fast echolocation sounds instead of mostly listening for the pickle to betray its location.

Even with the strategy switch, the bats aren’t completely making up for the noise nuisance, Jinhong Luo at Johns Hopkins University points out. A sensory biologist, he has tested noise effects on other bats but was not involved in this project. Looking at the new data, he notes that frog-eating bats in echolocating mode are slower to leave their perches and swoop than bats in eavesdropping mode. He also cautions about generalizing to the other 1,300-plus bat species. Many of them are already using echolocation to hunt insects and may not have a backup prey-finder method when noise complicates their foraging. 

Citations

D.G.E. Gomes et al. Bats perceptually weight prey cues across sensory systems when hunting in noise. Science. Vol. 353, September 16, 2013, p. 1277. doi: 101126/science.aaf7934.

Further Reading

J.P. Bunkley and J.R. Barber. Noise Reduces Foraging Efficiency in Pallid Bats (Antrozous pallidus). Ethology. November 2015, p. 1116. doi: 10.1111/eth.12428.

W. Halfwerk et al. Negative impact of traffic noise on avian reproductive success. Journal of Applied Ecology. Vol. 48, February 2011, p. 210. doi: 10.1111/j.1365-2664.2010.01914x.

S. Milius. A coast-to-coast picture of America’s cacophony of sounds. Science News. Vol. 187, February 21, 2015, p. 32.

S. Milius. Noise made by humans can be bad news for animals. Science News. Vol. 187, February 21, 2015, p. 22.