Echolocation Shapes a Bat’s Skull to Match Specific Frequencies

For a bat to be at its best in echolocation, it needs a good head on its shoulders. However, not all bats are the same when it comes to sensing their surroundings in complete darkness: some bats emit sonar waves through their mouths, while others do so through their noses. And depending on the echolocation method, one bat’s skull may be different from another’s.

A new study published in Royal Society Open Science found that echolocation influences the shape of bat skulls in several ways. The shape of a bat’s skull depends on how it produces sonar, as well as the specific frequencies it produces to find food or navigate environments. These factors cause variations in several bones and ultimately determine whether a bat will have a smaller or larger skull.

Learn more: Migration of bat surf storm fronts to save energy

See through the darkness

Bats evolved their flight and echolocation abilities more than 50 million years ago, according to Bat Conservation International. They are capable of producing high-frequency noises that bounce off various objects and, thanks to the returned echoes, they can perceive everything in an immediate area.

More than 1,000 species of bats use echolocation, a feat made possible by the larynx (or voice box); this specialized organ allows them to produce high frequency sounds through the oscillation of the vocal membranes.

According to a 2022 study in Biology PLOSThe bat larynx exhibits several unique adaptations not found in other mammals, giving it an impressive vocal range of seven octaves (while most mammals, including humans, have a vocal range of three to four octaves).

To better understand the association between echolocation and bat skull shape, researchers involved in the new study analyzed hundreds of specimens from museum collections.

“We now know that there is a link between the shape of bats’ skulls and the way they feed and make sounds,” Carlo Meloro, study co-author and paleobiologist at Liverpool John Moores University, said in a statement. “This is because in bats there is a clear dichotomy: some species emit sound using the mouth, and other species use the nose.”

Suitable for different frequencies

Researchers have determined that bats known to emit sonar signals through their mouths tend to have an upward-tilted skull, which can help project sound when flying with their heads held high.

Bats that signal through their noses, on the other hand, do not have the same angled skull and instead have larger ear bones and elaborate nasal discs.

The cranial differences between these two types of bats – “mouth transmitters” and “nose transmitters” – have to do with how they direct sonar signals. However, there is another level of skull variation that relates to the use of higher or lower frequencies.

The researchers determined that species using higher frequencies had shorter faces, while those using lower frequencies had larger ear bones.

“This relationship had already been anticipated by several researchers, who proposed that the skull could function as an acoustic resonator,” Meloro explained. Because high-frequency sounds have very short wavelengths, they are produced and received more effectively by smaller cranial and facial structures, while low-frequency sounds interact better with larger anatomical cavities.

The importance of echolocation

The method of sonar delivery is not the only factor affecting the shape of bat skulls; The new study also highlighted the role diet plays in echolocation.

Bats that feed primarily on insects need echolocation to target flying insects in the dark; On the other hand, fruit bats rely more on other senses like sight and smell, so it was assumed that echolocation would not have as much impact on the shape of their skull.

However, the researchers found that in fruit bats and insectivorous “nose transmitters,” species using higher frequencies generally had shorter faces. Although echolocation is not the primary way fruit bats find food, it still helps them avoid objects and land in the right areas where fruit is present. This suggests that even among different groups of bats, the need to produce higher frequency sounds determines skull shape in the same way.

Learn more: These bats glow green under UV light, but the reason remains a mystery

Article sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review them for scientific accuracy and editorial standards. See the sources used below for this article: