Big Brown Bat flying

Bat Signals: UTM prof studies evolution of echolocation

Blake Eligh

As a child, John Ratcliffe often wondered how his pet dog perceived the world. That early curiosity evolved into a career that has taken him around the globe, studying a variety of creatures, including moths in French Polynesia, nocturnal oilbirds in the Caribbean, harbour porpoises in Denmark and katydids, crickets and, especially, bats.

Ratcliffe’s subjects all have one thing in common—they find their way through the world at night, some through echolocation: sending and receiving sounds to figure out where they are in their environment, where their next meal might be or—in the case of insects with bat-detecting hearing—how to avoid becoming a meal for another creature.

Ratcliffe, an associate professor of biology, was named as a Canada Research Chair in Neuroethology—the study of the neural basis of behaviour. He was among 34 U of T recipients of the award in February 2016.

“I study how animals send and receive signals, and how ecology and evolution are correlated with sensory systems and the signals an animal uses,” he says. The results shed light on how vertebrate brains have evolved to place greater or lesser emphasis on different aspects of sensory and cognitive processing. “Visually-based animals have a bigger visual cortex, while animals who live in low-light conditions, like caves, have evolved differently,” Ratcliffe says.

“There’s an assumption that echolocoation is just the ‘poor man’s vision’ for situations where visual information is unavailable or unreliable,” he says. “We look at the ways that echolocation differs from vision, and the advantages echolocation may provide.”

“Imagine you’re driving, and everyone in the car is guessing how far away a landmark is. Using visual information, you would all (probably) make terrible guesses, but with echolocation, you would know exactly how far away that landmark is just by making a sound and counting until the sound comes back to you. Echolocators have a much better ability of ranging targets.

“When bats are closing in on a target, they’re producing echolocation calls 200 times a second, and processing that information in real time,” he says. “In contrast, humans watching a movie see a visual flow of just 20 frames a second. There’s an underlying assumption that echolocation is equal to or less than visual information. While it’s true that there’s no colour or binocularity, echolocation does other things and does them better than vision.”

In the field, Ratcliffe uses a wooden cross, studded with tiny microphones that pick up the echolocation signals of approaching bats. That data gives him a picture of the size and shape of the animal’s acoustic field of vision.

“We can position the bat in three-dimensional space and look at intensity of call, the shape, breadth and volume of the bat’s acoustic beam,” he says. “You can’t easily do that with vision. We can reconstruct the animal’s acoustic field of view in ways we can only assume about an animal’s visual field of view.”

Ratcliffe’s current research also looks at how echolocators track targets and make predictions about where moving prey will be next. “Bats make predictions about an insect’s future path based on how it has moved through space. If a bat doesn’t track an insect correctly, it’s a lost meal,” he says. “If an insect can’t track a bat, it’s a matter of life and death.”


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