The matriarch at the front of the heard might make a turn to the right which is immediately followed by elephants at the end of the herd making the same turn to the right. These synchronized movements occur despite the fact that the elephants' vision of each other is blocked by dense vegetation. Only recently have they learned that the synchronized movements are preceded by infrasonic communication. While low wavelength light waves are unable to diffract around the dense vegetation, the high wavelength sounds produced by the elephants have sufficient diffractive ability to communicate long distances. The typical prey of a bat is the moth - an object not much larger than a couple of centimeters.
Bats use ultrasonic echolocation methods to detect the presence of bats in the air.
The answer lies in the physics of diffraction. As the wavelength of a wave becomes smaller than the obstacle which it encounters, the wave is no longer able to diffract around the obstacle, instead the wave reflects off the obstacle. Bats use ultrasonic waves with wavelengths smaller than the dimensions of their prey. These sound waves will encounter the prey, and instead of diffracting around the prey, will reflect off the prey and allow the bat to hunt by means of echolocation. Refraction of waves involves a change in the direction of waves as they pass from one medium to another.