Detecting bats in your NatureHood
Bats use echolocation – a biological form of sonar – to maneuver through the darkness and hunt for insects. To echolocate bats create a high frequency ultrasonic sound in their throat that is emitted through the open mouth. Those ultrasonic sound waves move through the air, hitting and reflecting off of each object they encounter, much like ripples of water do as they move across a pond. As the sound waves reflect or ‘echo’ back to the bat, it receives the sound in each ear at a slightly different time and intensity, providing important 3D information about the bat’s environment. Based on the characteristics of the reflected sound, the bat can detect if an object is near or far away, if it’s moving, its shape and how big it is, and even the direction and relative speed of an object’s movement. It’s like having an ultrasound machine to guide you through the night sky! Bats echolocate regularly (but at different rates) as they move through the air, constantly updating their internal map keep track of their surroundings.
Although it’s not an exact science, you can get a good sense of which bat species you are hearing through one of our handheld bat detectors. These detectors are specially designed to detect bat echolocations and convert them from the ultrasonic range (i.e., higher than 20,000 Hz, beyond the normal range of human hearing) into the human audible range (i.e., between 20 Hz and 20,000 Hz). To begin monitoring for bats the detector should be tuned to 45.0 KHz; once something is detected you can use the tuning wheel to tune the detector frequency to the point where the pitch is lowest and loudest – this is the peak frequency of the bat’s echolocation signals, and that’s a key clue to identify the species you’re hearing!
So what do bat echolocations sound like through a bat detector? Some examples can be found below.
A bat pass is the sound of a bat passing your location. The sounds should start low, get loud, then low again. This counts as a pass. Try to count how many times a particular bat passes overhead, and remember that there could be more than one at a time! Listen to the recording below for examples of multiple passes being made by at least 3 different bats representing 2 species.
Eastern Red Bat and Big Brown Bat, full spectrum heterodyne microphone (A. MacDonald)
A feeding buzz is a very distinctive sound made by bats, and won’t be confused with anything else! As a bat locates and is about to catch an insect, it sends out a series of very high pitched series of ultrasonic clicks that can be compared to running your fingernail over the teeth of a comb (listen for this at around 00:26 seconds in the recording below). By emitting these buzzes, the bat can zero in on its prey’s exact location, allowing it to scoop the insect into its mouth using its tail membrane.
Silver-haired Bat (Credit: Maryland Acoustic Call Library and Species Accounts)
Big Brown Bat (Credit: Maryland Acoustic Call Library and Species Accounts)
Little Brown Myotis/Bat (Credit: Maryland Acoustic Call Library and Species Accounts)
Hoary Bat (Credit: New Mexico Bat Call Library, W. L. Gannon)
Ticks & Pops
“Ticks” and “pops” are very short, distinct sounds – similar to the sound of typing on a keyboard or typewriter, with a punctuated sound at the end.
Taps, putts and knocks
“Taps”, “putts” and “knocks” are longer, distinct sounds that could be described as hammer taps, knocking gently on a wall or a hitting a tennis ball hitting with a racquet. You can mimic these sounds by forcing air through your lips while trying to keep them sealed.
“Chirps” sound similar to bird chirps and are typically short. There may be a change in pitch at the end of the chirp.
“Flaps” are distinct from ticks and taps and sound a lot like wings flapping. Individual flaps may be a bit less distinct from one another than with ticks and taps.
Have a listen to some examples of each of these sounds in the following video*. The description of each sound is quite subjective and it ultimately takes a bit of field practice with the same bat detector to become familiar with how they differ – and how the detector transmits them in the audible range. Once you’re familiar with the texture and characteristics of each bat species’ calls, you can start to discern multiple species passes while using your detector, as explained in the examples here.