Echolocating bats use cognitive maps of sound to find their way home in the dark

Amazing stuff!

Why did they choose such tiny bats to attach a GPS device? "Study with 6-gram light bats"

"... In a new study, researchers placed GPS trackers on tiny pipistrelle bats living in Israel’s Hula Valley and relocated them to various points within a three-kilometer radius. Some of the animals were also blindfolded or had their sense of smell blocked. Surprisingly, even when forced to rely on echolocation alone, 95% of bats were able to find their way back to their roosts within minutes. The findings suggest that this ability allows bats to create complex mental “maps” of their surroundings, complete with various types of acoustic “landmarks,” which they use to navigate across long distances.

The researchers were also surprised to discover that, when possible, the bats used their vision to enhance navigation. ... even with such small eyes, they can rely on vision under these conditions.” ..."

"... In addition to the field experiments, the team created a detailed map of the entire valley. “We wanted to visualize what each bat experienced during flight and understand how they used acoustic information to navigate,”  ...

The model revealed that bats tend to fly near environmental features with higher ‘echoic entropy'—areas that provide richer acoustic information. “During the localization phase, bats conduct a meandering flight that, at a certain point, changes to a directional flight toward their destination, suggesting they already know where they are ..."

From the editor's summary and abstract:

"Editor’s summary

Insectivorous bats are well known to use echolocation to catch prey and navigate around obstacles. It has also been shown that more visually guided fruit bats have spatial cognitive maps of their environment. Goldshtein et al. placed minuscule GPS trackers on tiny pipistrelle bats in conjunction with temporary blocks of vision and olfaction. The authors found that the bats could still navigate across kilometer scales using only echolocation. Thus, echolocation may not only allow for local navigation, but might also translate into an acoustic cognitive map of the environment that the animals can use to navigate over long distances. —Sacha Vignieri

Abstract

Bats are known for their ability to use echolocation for obstacle avoidance and orientation. However, the extent to which bats utilize their highly local and directional echolocation for kilometer-scale navigation is unknown. In this study, we translocated wild Kuhl’s pipistrelle bats and tracked their homing abilities while manipulating their visual, magnetic, and olfactory sensing and accurately tracked them using a new reverse GPS system. We show that bats can identify their location after translocation and conduct several-kilometer map-based navigation using solely echolocation. This proposition was further supported by a large-scale echolocation model disclosing how bats use environmental acoustic information to perform acoustic cognitive map–based navigation. We also demonstrate that navigation is improved when using both echolocation and vision."

ScienceAdvisor

Echolocating bats use an acoustic cognitive map for navigation

Bats use an acoustic cognitive map for navigation (original news release)

Echolocating bats use an acoustic cognitive map for navigation (no public access)

How a disappearing ear bone turned bats into masters of echolocation

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"... Then, in 2015, Benjamin Sulser, a University of Chicago biology student on the hunt for a thesis project, took detailed 3D images of the inner ear of a bat skull. But he couldn’t find a feature common in virtually all mammals—a bony tube that encases the nerve cells and connects the ear to the brain. Thinking he’d made a mistake, he and Luo imaged the skulls of two more related species using a computed tomography scanner, with similar results. The researchers realized they might have stumbled across an answer to a mystery that had bedeviled bat biologists for 2 decades—and an explanation for why some families of bats had such a diverse echolocation arsenal. ...

For years, bats were divided into two groups: big fruit bats, which don’t generally echolocate, and small bats that hunt by sound. But in 2000, a genetic analysis revealed bats had actually diverged into two different groups some 50 million years ago: one group that included the large fruit bats and some of the echolocating insect eaters (known as Yinpterochiroptera, or “yin”), and another group that included the rest of the small, sound-hunting bats (known as Yangochiroptera, or “yang”). The latter make up 82% of the 1250 known echolocating species of bats.

But until now, no one could find a physical difference linked to the genetic split between the two groups. After Sulser’s discovery, the duo spent 5 years scanning the skulls of 39 bat species. In 24 of 26 yang bats they scanned, the bony nerve channel was missing or contained large holes making it resemble lace, Sulser and Luo report today in Nature. ..."

From the abstract:

"... Here we report the observation of highly derived structures of the spiral ganglion in yangochiropteran bats: a trans-otic ganglion with a wall-less Rosenthal’s canal. This neuroanatomical arrangement permits a larger ganglion with more neurons, higher innervation density of neurons and denser clustering of cochlear nerve fascicles. This differs from the plesiomorphic neuroanatomy of Yinpterochiroptera and non-chiropteran mammals. The osteological correlates of these derived ganglion features can now be traced into bat phylogeny, providing direct evidence of how Yangochiroptera differentiated from Yinpterochiroptera in spiral ganglion neuroanatomy. These features are highly variable across major clades and between species of Yangochiroptera, and in morphospace, exhibit much greater disparity in Yangochiroptera than Yinpterochiroptera. These highly variable ganglion features may be a neuroanatomical evolutionary driver for their diverse echolocating strategies and are associated with the explosive diversification of yangochiropterans, which include most bat families, genera and species."

How a disappearing ear bone turned bats into masters of echolocation | Science | AAAS

Evolution of inner ear neuroanatomy of bats and implications for echolocation (no public access)