When Froggy Goes A Courting

Mark Bee believes that frogs hold the answer to an inharmonious human problem.

For most of us, a Minnesota marsh full of courting frogs in the late spring and early summer is a place so loud that we can barely think. “Individual frogs at a distance of a meter can call at 90 decibels—as loud as a truck zooming by on the highway,” says Mark Bee, assistant professor in the Department of Ecology, Evolution and Behavior. “When you have 200 of those frogs in a small area, you can shout as loud as you possibly can, and nobody will hear you at the opposite end of the pond.”

Yet Bee does some of his best thinking and observing in this cacophony. Wearing hip-high waders and sometimes earplugs, he makes nocturnal visits to area ponds to look for the frogs not making any sounds—the ones who have successfully found mates. He captures these pairs and takes them to steel sound chambers in his Animal Communication Lab, where the females demonstrate their ability to distinguish the calls of males of their own species from the utterances of others. Bee believes that his studies could eventually benefit hearing-impaired people who have trouble picking out single voices in a noisy setting.

In acoustical studies, the "Cocktail Party Problem” is the official term for the difficulty humans have in understanding speech in noisy social settings. “A lot of non-mammals also encounter and solve this type of problem,” Bee says. Focusing on the gray treefrog (Hyla chrysoscelis)—a species blessed by abundance and the simple mating call of its males—he subjects the females to recordings of frog calls in different combinations, locations and intensities in the sound chamber to observe their responses. If they can distinguish the calls of their own kind, they move toward the source of the sound. “These experimental procedures let us look at the neuro-mechanism of what the female perceives,” he says. “My research won’t solve human deafness, but it might allow us to learn how animal nervous systems have evolved to solve the ‘Cocktail Party Problem.’”

Bee’s fascination with sound goes back to his childhood music lessons. In college he found that he could combine his acoustical inclinations with his interest in biology. Before joining the biological sciences faculty in 2005, he spent several years as a postdoctoral fellow in Germany at the University of Oldenburg where he studied auditory neurophysiology in starlings.

Occasionally, as he drains pond water from his boots within a swarm of mosquitoes, he misses the study of birds. But when he watches a female gray treefrog in his lab dart in the direction of a male’s call amid a dissonance of other sounds, his regrets fade. “They’re just little machines when we put them on the floor in the sound chamber—they’ll go to the speaker over and over again,” he says. “That’s what makes them perfect.”

— Jack El-Hai