Scientists seek bat detectives

The night is full of noises. People can hear some of the sounds, such as car horns and crickets. But flitting overhead, bats call and chirp in sounds too high-pitched for our ears to detect. Now, scientists have altered these calls so that people can hear them— and see them. The reason: They want your help in identifying millions of these calls. All you need is a computer. The data you and other citizen scientists provide will contribute to understanding the environmental health of places that bats — and people — call home.

This Bat Detective project has awebsite. It displays millions of sound recordings from a project called iBats. On scheduled nights, volunteers across Eastern Europe and Western Asia drive their cars at a specific speed and in a set pattern. A recorder on top of their car records the sounds of the night, from people talking to shrill bat cries. Once the volunteers have completed their routes, they send the recordings to scientists in London and New Zealand. In each place, teams of scientists use computer programs to transform the bat sounds. This makes them audible to the human ear.

The project is a collaboration of many scientists at the University College London, the London Zoo, the Bat Conservation Trust, Bat Life Europe, the University of Auckland (in New Zealand) and the citizen science site Zooniverse.

Bats make a lot of noise. They use some sounds to communicate. The bats emit other calls to navigate the darkness through echolocation. It’s the bat version of sonar. The animals’ high-pitched calls bounce off of objects in their path, echoing back to the bats.

Kate Jones, the director of iBats and a founder of Bat Detective, says that the constant calling by bats makes them a good target for research. “They leak information about themselves and about the environment all the time,” she explains. “Bats call to navigate, to find food and mates. They even blockthe calls of other bats.”

So that people can listen in, the scientists are now replaying the bats’ sounds at a slower speed.

Sounds are produced by vibrations — a rhythmic pulsing back and forth. This can be produced in many ways, from hitting the skin of a drum to sending air across muscles that tighten and release our vocal chords. Those vibrations produce sound waves, which are alternating highs and lows of pressure. These waves have a measureable distance between one peak and the next. Long waves are low sounds; shorter waves are higher pitched. The lengths of the waves are described in terms of frequency — how many waves occur in a given length of time. Low-pitched sounds have long wavelengths; shorter wavelengths produce higher-pitched sounds.

Bats emit echolocation calls at very high frequencies (many wavelengths per unit of time). Computers can slow recordings of these to a frequency our ears can hear. The end result, Jones says, sounds “like a bird chirp.” Computers also can display these sound pulses as a visual map. They portray background noise in blue to red. Louder sounds jump out in yellow and orange. With these sight and sound clues, the scientists hope that bat detectives can find bat calls from within a mix of other sounds.

Want to try? All you have to do is go to the site and click “classify.” The program will take you through an image and sound recording that contains a bat call. Highlight the peaks of sound on the image with your mouse. Look at the field guide below to see whether it resembles a bat call, an insect call or a machine noise. Now click the buttons at the right of the screen to confirm your choice.

Many of the images and sounds are bat-free, with only random clicks or cricket chirping. But all of this sound is useful information. Jones wants to use the data collected by this project to monitor biodiversity — the variety of organisms living in a particular place. Many species of bats and insects might indicate a high level of biodiversity. Over time, the nighttime sounds in an area might change in intensity and audio diversity. Citizen scientists using Bat Detective will be able to track these changes over time, giving biologists important clues to how people and environmental changes in an area are altering the diversity of critters sounding off there. 

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Power Words

biodiversity     (short for biological diversity)  The number and variety of species found within a localized geographic region.

citizen science  Scientific research in which the public — people of all ages and abilities — participate. The data that these citizen “scientists” collect helps to advance research. Letting the public participate means that scientists can get data from many more people and places than would be available if they were working alone.

computer program  A set of instructions that a computer uses to perform some analysis or computation. The writing of these instructions is known as computer programming.

echo    To bounce back. For example, sound bouncing off walls of a tunnel, and source. Radio waves emitted above the surface can also bounce off the bedrock underneath an ice sheet — then return to the surface returning to their.

echolocation   (in animals) A behavior in which animals emit calls and listen to their echoes that bounce back off of solid things in their environment. This behavior can be used to navigate and to find food or mates. It is the biological analog of the sonar used by submarines.

ecosystem  A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.

frequency  The number of times a specified periodic phenomenon occurs within a specified time interval. (In physics) The number of wavelengths that occurs over a particular interval of time.

sound wave  A wave that transmits sound. Sound waves have alternating swaths of high and low pressure.

vibrate  To rhythmically shake or to move continuously and rapidly back and forth.

wavelength  The distance between one peak and the next in a series of waves, or the distance between one trough and the next. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.