Scary? Bloodsucking? Wicked creatures of the night?
Although they do have strange little faces, bats are definitely not the hair-tangling draculas often portrayed in horror movies. For Christine Portfors, assistant professor in biology at WSU Vancouver, bats offer a unique opportunity to study hearing and communication. She even has a specially outfitted laboratory — built for her in 2001 — affectionately dubbed the Batlab.
A model for human hearing
Bats are singular in a number of respects including the large size of their auditory system. The flying mammals use echolocation — with both audible and ultrasonic vocalizations — to catch food and orient through their environment at night. Though they do have vision, they literally use the echoes to “see” their environment.
Emitting high-pitched cries, their sound waves bounce off objects, creating an echo the bat uses to determine the characteristics of the insect — or obstacle — looming ahead.
“In the big picture,” explained Portfors, “we are working to gain a better understanding of how humans process vocalization or speech — and how age-related hearing loss impacts that processing. Echolocation in bats is one model that is helping us understand how specific cells in the brain “encode” — or read and interpret — complex sounds.”
Studying the mustached bat, Portfors has discovered that certain neurons, in a part of the brain called the inferior colliculus, respond selectively to specific social vocalizations and not others.
“This is significant in that prior research has looked at higher order processing in the cerebral cortex, but not at mechanisms this early in the hearing pathway,” she said.
“In hearing problems, especially with problems discriminating different types of speech sounds, you want to pinpoint where the trouble is actually occurring. Though we tend to assume that is usually within the ear itself, problems can also arise in the brain,” said Portfors.
“Once we discover how sounds are encoded along the normal hearing pathway, it will be a critical first step toward the prevention and reduction of speech processing problems in humans.”
Signature sounds
To record the ultrasonic frequencies of bat communication, Portfors and her team must use a specialized microphone together with software capable of analyzing the sound waves.
“One of the most interesting parts of our research is cataloguing the wide variety of vocalizations bats have,” she said. “We are showing that bats are very social creatures — using acoustic communication not only to find food and to navigate, but also for showing aggression, mating, and mother-pup interactions. The female uses her ‘signature sound’ to help locate her pup when she returns to the roost after foraging.
“Hopefully our work can help people understand that bats are really very interesting and dynamic animals — they aren’t just out there flying around by themselves at night.”
“In the Pacific Northwest, for example, we have insectivorous bats that eat about 50 percent of their body weight in insects each night — primarily mosquitoes, moths and beetles,” said Portfors. “Without bats, the need for pesticide use would greatly increase. Bats are also important in other parts of the world for pollinating flowers and dispersing seeds. But as humans continue to destroy their habitat — cutting down old growth forests and closing abandoned mines — bats are becoming a threatened species.”
Word of warning
Though a very tiny percentage of bats become infected with rabies, they can be carriers of the virus — so never pick up a bat with bare hands. It’s best to admire them from a distance.