Bats zooming through the air at dusk know where they're going, despite flying in near darkness; they detect their ultrasound calls bouncing off objects and use these echoes to find their way around. Marianne Jensen,Cynthia Moss and Annemarie Surlykke decided to see which of these numerous echoes bats rely on for orientation().
Collecting big brown bats from attics in America and a colony in Canada,the team trained the animals to fly through a hole in a large net suspended across a dark room, rewarding them with a juicy mealworm. They placed a camera tripod next to the hole for the bats to use as an `acoustic landmark' that reflects their calls. To reconstruct the bats' flight path as the animals tried to locate their dinner, the team filmed them with high-speed cameras. They recorded the bats' calls to correlate these with their flight behaviour. When the team placed the tripod near the hole in the net, the bats had no trouble finding the hole. But when the team moved the tripod to another position, the bats crashed into the net next to the tripod and inspected the area of the net where the hole should have been; they clearly ignored the net's faint echoes and used the tripod as an acoustic landmark. When the team took the tripod out of the room, the frustrated bats spent even longer desperately searching for the net opening. The team concludes that bats can learn to rely on a single echo-reflecting object to figure out where to go.
