Answer to Question #91710 in Mechanics | Relativity for Lacey

Question

When a bat walks over ground searching for insects (its prey), it is usually guided more by hearing an insect than by seeing it because a bats vision is poor and they search at night. However some types of bats can detect and capture an insect, such as a moth, when both are in fight. Although the bat flies quickly, it can home in on an insect and nab it. How does the bat detect not only the presence of the insect but also its direction and speed of flight?
Why do bats have a better time nabbing flying moths near a mercury vapor lamp (commonly used as a street lamp) than over an open field? Why does the advantage disappear if the lamp is a sodium vapor lamp?
Bats can roost in deep, dark caves flying in and out to forage for food. In the complete darkness of a twisting passage of a cave they do not fly into the walls. How do they do that?

Answer 1

Q: How does the bat detect not only the presence of the insect but also its direction and speed of flight?  

A: How do people catch things under the sun? The sun emits light, the light hits objects, reflects (and refracts) in them and rebounds to our eyes. Then we act according to what we see. Now imagine we need to chase something in the night. This would be way more easy if we had a torch on our head.

Bats use echolocation in the night time. Instead of the light previously discussed, they emit ultrasounds from 20 to 100 KHz. Wavelengths corresponding to these frequencies are enough to avoid diffraction. The sound pitches are produced by the bats' mouth, hits prey and rebounds to bats' big ears.

Q: Why do bats have a better time nabbing flying moths near a mercury vapor lamp (commonly used as a street lamp) than over an open field? Why does the advantage disappear if the lamp is a sodium vapor lamp?  

A: The study conducted by Svensson and Rydell in 1998 showed that the light from mercury lamps interfere with tympanate moth defense mechanisms and negatively affects moths' vulnerability. Moths become less quick to hear the sounds from the bats. This does not happen under the light of the sodium vapor lamps since it is less attractive to bugs.

Q: How do the bats avoid hitting the walls when they fly in the completely dark caves?

A: The answer to this question is too echolocation. By means of such a way of exploring the geometry of the surrounding space bats can fly in the complete darkness as birds in the daytime.