Bats and Fog

Abstract

ON windless evenings fog commonly forms in dense, sharply defined patches, especially in sheltered bays of ponds. As the evening progresses and the temperature falls, these patches may grow and coalesce, advancing over the pond but maintaining a sharp front at which visibility changes profoundly within a few metres. In such conditions insectivorous bats hunting over the water have been observed to turn back at the fog front as if at a solid wall, even though their hunting area may become severely restricted. This behaviour suggests that fog may have a direct effect on echo location.