"It's like a sail or a plane. When you change the curve of a wing a little bit, you get improved lift. But if you curve it too much, the bat ?or plane ?may suddenly lose lift, hitting a stall point and falling out of the air. These receptor cells give bats constant feedback about their wing positions," said Zook, who has studied bats for more than 30 years, focusing on echolocation and the bat auditory system. The bat's sense of touch has been a side interest since the early 1980s.
To test his hypothesis, Zook removed the delicate hairs from bats' wings with a hair removal cream. Then he let them fly. The bats appeared to fly normally when following a straight path, but when they'd try to take a sharp turn, such as at the corner of a room, they would drop or even jump in altitude, sometimes erratically. When the hairs grew back, the bats resumed making turns normally.
"It was obvious they had trouble maintaining elevation on a turn," he said. "Without the hairs, the bats were increasing the curve of their wings too much or not enough."
The bats' flight behavior also changed based on the area of the wing where the hairs were removed. For example, when Zook removed hairs along the trailing edge of the wings and on the membrane between the legs, the bats were able to fly and turn effectively, but they tended to pitch forward because they couldn't control their in-flight balance.
Zook's research also points to the importance of a second type of receptor cell in the membranous part of bats' wings. Nerve recordings revealed that these receptors respond when the membrane stretches. Zook calls areas on the wing where these stretch-sensitive cells overlap "sweet spots" because they are where bats like to snag their prey. In the lab, Zook shot mealworms covered with flour into the air and recorded how the bats cau