Specially Evolved Brain Structures Make Bats Better Hunters

BY HAVING CERTAIN NEURONS POSITIONED CLOSE TOGETHER, BATS CAN PROCESS SENSORY INFORMATION QUICKER. IVAN KUZMIN/SHUTTERSTOCK

Catching flying insects is a tricky business, especially when you can only spot them using sound. Bats are masters of this, using echolocation to visualize their prey, and now researchers have found that a special structure in their brains lets them process this information extremely quickly.

Echolocation is a kind of biological sonar used by certain animals to navigate their surroundings and hunt prey. It involves emitting calls – generally clicking sounds – and then listening to how the calls are returned from the environment. Echolocation is famously used by bats and dolphins, but it can also be observed in all other species of toothed whale, as well as shrews and swiftlets.

Bats are known for lurking in low light, spending their days hanging upside down in caves, trees, and attics, but at night they come alive, heading off into the darkness in search of food.

When foraging, they have to process more than 120 echolocation clicks every second, a rather impressive feat. So, researchers at Johns Hopkins University decided to test whether this requirement has led to the evolution of a unique brain structure to maximize efficiency. Their findings are published in The Journal of Neuroscience.

They conducted their research using the species Eptesicus fuscus, otherwise known as the big brown bat, which is native to the US, the Caribbean, Central America, and the most northern part of South America.

The scientists looked at the bats’ superior colliculus (SC), a layered structure found in the brains of mammals. It is important in processing sensory information and helps its owner to orient themself within their environment. The SC has mainly been studied in animals that primarily rely on sight, so the researchers decided to test whether being reliant on sound and echolocation affected its structure.

Recording the activity of the SC in four bats whilst prey location was manipulated, the team found that both sensory and motor neurons were present in every layer of the SC. Their proximity to one another was thought to help the bats to process information extremely quickly. Neuron activity also changed as the bats got closer to their prey, decreasing auditory response time. 

A bat tracking and intercepting its prey during the experiment. Melville Wohlgemuth

"The real benefit of using the bats is that we can just measure how quickly the animal is vocalizing so we have a quantitative measure of how much information that animal is taking in at that time," explained lead author Dr Melville Wohlgemuth to BBC News.

"It has to take in lots of information and crunch that data very quickly to do something with it," he added.

The adapted SC in the brain of bats is just one of many examples of how evolution has allowed different species to occupy their own specific ecological niches.