The diet of the majority of bat species consists of insects. Most insects are relatively small in size, yet bats can eat their body weight in insects every night! This is even more astounding that they find these insects flying in the dark. Bats are able to accomplish this extraordinary feat through the use of echolocation, but what is echolocation and how do bats use it?
Echolocation is made of sound that is emitted through a source, the bat. Once the sound hits an object it bounces back towards the bat and paints a picture depending on the velocity of the sound itself. However, sound waves follow a few rules.
1. Amplitude- Loudness, or height of sound wave
2. Wavelength- Distance from peak to peak in a sound wave.
3. Frequency- Pitch, number of cycles per second
4. Velocity- Is wavelength times frequency
Shorter wavelength created a higher frequency. The higher the frequency the greater detail a sound will bounce back. Having said that, the sound wave itself has a much shorter range, while the lower frequencies has a much longer range. With the longer range, sound waves come back with less detail, but small insects are blind to these frequencies. This gives an immense advantage to the bat. However, there are many different times where higher and lower frequencies have an advantage (Feldhamer 2007).
Higher frequencies produce less noise, which goes unnoticed by most insects. Also, greater detail is another benefit of using higher frequencies. The detail is so great that it even gives the size of the prey including small insects like the mosquito. Regardless, of all the advantages echolocation gives to bats it does have its downsides. Bats cannot hear when emitting the sound because the sound is so loud they have to close their ears, but how does a bat use these frequencies to find food?
There are three phases where bats are searching for their prey. Once they locate prey bats enter the approach phase, which then begins the terminal phase. The bats use constant frequency during the search phase, which consists of lower frequencies, and is used for detecting movement. Once prey has been identified and located, the bat begins the approach phase where higher frequencies are used. This gives the bat a detailed look at what their target is. If the bat identifies the target as food, the terminal phase begins (Feldhamer 2007). Very high frequencies are used at this point, which creates a terminal buzz that one might hear sometimes at night as a quick chirping sound. The end of the terminal phase is when the bat captures the insect. Despite all the advantages of echolocation, some insects have evolved to deceive sound itself.
Some insects can hear the echolocation of bats, while others can “jam” the sensory of the bats. Some species of moths accomplish this by emitting high frequency clicks coming from the tymbal organs (Feldhamer 2007). This interferes with the bats frequency and will make the bat miss the target.
Feldhamer, George A. Mammalogy: Adaptation, Diversity, Ecology. Baltimore: Johns Hopkins UP, 2007. Print.