When It Comes to Echolocation, Some Bats Just Wing It

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More than 1,000 species of animals use echolocation, including most bats, all toothed whales, and some small mammals. They do it in different ways, from vibrating their throats to clicking their tongues to flapping their wings to using a special organ. Some use echolocation to find prey, while others use it to avoid predators, and some even use it just for navigation. Most people realize bats create a sound from their larynx to perform these functions, but not all bats do. Some may use their wings.

Photo by James Wainscoat (unsplash.com)

Donald R. Griffin, zoologist at Harvard University, coined the word echolocation in 1944. His short (650-word) paper in the research journal Science carried the intriguing title "Echolocation by Blind Men, Bats and Radar". He briefly mentioned how bats do it in the dark with ultrasonic cries, how blind people mimic it by tapping canes, how ship captains use whistles in fog to locate cliffs or buoys, how ships use fathometers to detect the sea bottom depth or submarines, and how airplanes use radio altimeters to determine how high they are.

As for bats, genetically speaking, there are two groups: large fruit bats (which usually don't echolocate) and some echolocating insect eaters (collectively called "yin" after their taxonomic name), and the other group consisting of other small bats that use echolocation (called "yang"). About 70% of all bats use echolocation.

Bats that echolocate produce a high pitched cry from their vocal cords which then comes out of their mouth or nose. They can modulate the pitch to several wavelengths between 30,000 and 80,000 hertz. It reflects off objects, and bats can then judge the distance away, the texture, and the direction it may be moving.

A simple tutorial about bat echolocation from its voice (YouTube)

However, in 1988, Edwin Gould of the National Zoological Park, Washington, DC made a discovery about two species of Philippine dawn bats known to not create echolocation sounds. He studied 4,000-5,000 of them in caves in Kuala Lumpur, Malaysia and noticed that they have to fly in total darkness 300 meters (984 feet) to reach a thin ray of light. They make a "clapping, raindrop-like" sound that stops the moment they reach the light or when the cave itself is illuminated artificially. 

Philippine dawn bat (inaturalist.ca)

Gould tested them in a dark room and got the same response to light. So, he painted the tip of one wing and noticed that it left a mark on the other wing in the dark but not the light. When he plugged their ears with cotton, he saw that they flew shorter times and with more hesitation. Navigation around objects in the dark were not found to occur any better between bats with plugged or unplugged ears. He determined that they were making the sound by hitting their wings together, but he did not know why. 

Researchers at Tel Aviv University in 2014 expanded on that study with a different species of fruit bats that don't use echolocation. They found landing sites in the dark but not very accurately, and they couldn't navigate around obstacle courses, much like Gould's work. The clicking sounds from the wings were sometimes audible to humans. They, too, confirmed that wing action seemed related to the clicking sounds by using high-speed videos of the bats in flight.

• Their mouths were closed when sounds were made. Sealing their mouths did not stop the clicking.
• Clicking synced with wingbeat rate.
• Covering wing tips with tape prevented clicking sounds.

But the researchers could not identify exactly how these bats produce the clicking. 

Moreover, bat and bird wing structures are different. Coincidentally, birds called manakins are known to make loud, short "snaps" over a wide range of frequencies with their wings as they fly. 

Two types of manakins (Wikipedia)

By studying high-speed videos, scientists have determined that how they make the snaps is divided into four mechanisms:

• above-the-back wing-against-wing claps
• wing-against-body claps
• wing-into-air flicks
• wing-against-tail feather interactions

Watch the short YouTube video below for 3 differences in how birds and bats fly.

Differences between bats and birds in flight 

The secret to these bats’ hunting prowess is deep within their ears

https://www.popsci.com/animals/bat-ear-echolocation-evolution/

https://en.wikipedia.org/wiki/Animal_echolocation

https://www.studysmarter.co.uk/explanations/physics/waves-physics/echolocation/

Echolocation is nature’s built-in sonar. Here’s how it works.

https://www.nationalgeographic.com/animals/article/echolocation-is-nature-built-in-sonar-here-is-how-it-works

Echolocation in bats

https://www.britannica.com/science/sound-reception/Echolocation-in-bats

Summary video on bat echolocation (4:33)

https://www.youtube.com/watch?v=laeE4icRYp4