The mystery of how bats negotiate obstacles in darkness has fascinated yet eluded scientists for centuries. In the seven decades since an undergraduate from Harvard coined the term 'echolocation,' bats have inspired the development of man-made sonar systems that can locate mines and underwater hazards, pinpoint shoals of fish for commercial fishing, and serve in communications from submarines.
The great grandfather of bat research is Lazzaro Spallanzani, a priest, physiologist and zoologist in late 18th century Italy. He conducted a series of careful and ingenious experiments, first noting that blinded bats could fly and avoid obstacles just as well as seeing bats. The zoologist Charles Jurine added another significant discovery: if the ears of bats were plugged with wax, they collided helplessly with obstacles.
Despite numerous experiments confirming Jurine's discovery, Spallanzani struggled to explain how the bats' ears appeared to be more useful than its eyes for seeing. He ended his experiments without a clear answer, admitting that somehow blinded bats use their ears when negotiating obstacles, incredible as it seemed. Spallanzani's experiments were not widely known or accepted by his contemporaries. For the next 140 years, the prevailing scientific view was that bats somehow used their sense of touch to navigate.
But Spallanzani was missing a major piece of the puzzle. He thought bats did not produce any audible sounds that as they flew. It was not until the 1930s that physicist G. W. Pierce developed an apparatus that could detect sounds above the frequency range audible to humans or ultrasonic sounds as they are known. In 1938, Harvard undergraduate Donald Griffin brought a cage of bats to Pierce's lab. The supposedly silent bats were in fact emitting intense sounds in the ultrasonic range.
Griffin worked with Robert Galambos to learn about how bats used the ultrasonic sounds they produced in orientation. Together, they showed that the sounds the bats produced were necessary for normal flight, and deafened or gagged bats helplessly collided with obstacles. Bats were actively probing their environment, emitting sounds and then locating obstacles using the echoes that returned to their ears. Griffin called this type of orientation 'echolocation,' although bats sense much more than just the location of objects. Later research demonstrated that bats can determine the distance to objects, their size, texture, and velocity all through characteristics of their reflected echoes.
Today, the remarkable abilities of bats are the inspiration for building better sonar systems. Bat echolocation is still more sophisticated and effective than any man-made sonar, and scientists around the world are working to fully understand the details that allow bats to perform aerial acrobatics at high speeds, in cluttered environments, amidst potentially interfering sounds — all using their mouths and ears.
Related Links:
- Science: The World Through a Bat's Ear