Using SonoBat for bat talks and bat walks

We have used SonoBat in a number of public presentations with enthusiastic response. When used with an LCD projector, it can provide vivid imagery to complement a talk explaining and demonstrating bat echolocation. It is particularly helpful to use before going out and acquiring some live bat calls. Begin by explaining what a sonogram displays: time on the horizontal axis, frequency (i.e. pitch) on the vertical axis, and amplitude or volume by color intensity. The program comes with some useful synthesized tones to help those unfamiliar with a sonogram display get acquainted.

Using some previously saved files, you can demonstrate the variety of bat calls, and talk about why they are different. For example, long flat calls are typical of bats that fly in the open and do not need as much immediate information about their surroundings, whereas short, steep calls (with a higher call repetition rate) are typical of bats that forage among clutter and require more information about their surroundings for navigation and prey detection. SonoBat lets you display file sequences as examples, and also lets you compare such different calls side by side at the same scale. In addition, as you display these different views, you can play the call sequences so your audience can hear the differences that they see. Next, you can show and play some feeding buzz sequences to demonstrate how bats alter the repetition rate and shape of their calls to acquire more information during prey pursuit. (Example feeding buzzes and other sequences come with the program.)

Remind people that the bat sounds they are hearing are reduced in frequency to make them audible, and slowed in time— everything the bats do is much faster. To really bring home that point, have someone say "Ahhhhhh" while you record their voice with a time expansion detector, then play it back. When everyone realizes the low-pitched warble they hear are the oscillations of the person's vocal chords, it puts the high range of the bat calls right into perspective. If you have some kids on hand, have them say a simple word like "batcall" to record and play back— they get a big kick out of that. If you display the human voice recording on the SonoBat display (turn off any filter setting to display the predominant low frequencies), it lets you visually compare and reinforce this concept. Turn on the SonoBat ruler and place it at 20 kHz, and explain that all of our human hearing range is below the ruler, and that leaves all of the large range of the sonogram display above the ruler for the bats.

Here's another activity that works well with kids: have them echolocate like a bat. If you have a large flat wall (rock or building), have them start at some distance from it and clap their hands once to hear the echo bounce off the wall. Then have them walk toward the wall while clapping about once a second. They'll get the feel for how the timing of the echo changes as they approach the wall. This works best if each "bat" can make the "flight" one at a time. They'll be thrilled to know that they can echolocate just like a bat. (And if anyone mentions anything about "Blind as a bat," tell them that bats have an expression among themselves: "Deaf as a human." Explain that just because we get around by predominantly using our eyes, it doesn't mean that we don't use our ears; and vice versa for bats.)

Before you send them off, you can record a clap echolocation with a time expansion unit and display it in SonoBat. You will be able to see the call and echo, and determine the timing. (Turn off the filter to display the predominant low frequency, and select the call/echo in real time mode and process into a high resolution standard view display for analysis.) With a little math, you can determine your distance to the wall.

One more fun kid activity to help them understand the world as bats "see" it: our vision is passive, it takes in available light which is usually continuous and therefore we see a continuous image. Bat echolocation is active and intermittent. The only echoes they get back come from the sounds they actively make. This has two consequences: 1) because they don’t emit calls continuously, they get intermittent echoes, and 2) because they are emitting the sound to get the echoes, the sound energy falls off considerably with distance (inverse square law). As a result, they get "snapshots" of the world around them that fade out with distance away from them. Your bat kids can simulate this by blinking their flashlights to get their own "snapshot" views of their world. (Just try to keep them from running into things and each other!)

Now head out with the group and look at some real bat calls!