“The world had a way of speaking to you if you let it; the trick was learning to hear” – Justin Cronin (American novelist)
“Change comes from listening, learning, caring and conversation.” — Gwen Ifill (American journalist)
“Wisdom is the reward you get for a lifetime of listening when you would have rather talked.” – Mark Twain
“If you’re not listening, you’re not learning.” — Lyndon B. Johnson
Listening is learning and when we listen, we learn that nature speaks to us. Listening to nature and interpreting sounds lets us understand animal behaviors. The GSC works with fellow researchers to listen in on what animals are saying. And that communication allows us to paint a picture of animal behavior.
As you probably know, the world is noisy. Just step outside and listen and you may hear cars driving by, people talking, birds chirping, or wind blowing through the trees. All of these sounds are in the auditory range or sounds that humans can hear.
Some small-bodied animals are able to vocalize at very high frequencies; sound that is well outside of human hearing. Animals like bats, rodents, and small lemurs choose to vocalize in this high frequency range. It is beneficial for small animals that are often prey items to communicate in the ultrasonic spectrum. It’s quieter, so it’s easier to talk to each other and the predators can’t hear so it’s safer. Researchers use technology to record ultrasonic vocalizations, referred to as USV’s. A small omni-directional microphone elevated into the sky will record ultrasonic noises and store those sound files on a bat detector.
Rooftop bat detector – GSC; photo courtesy Rada Petric
Using software, we can take those files and view them on a spectrogram, lower the frequency and listen to them on the computer, and use this information to understand animal behavior.
Bats use echolocation which is ultrasonic pulses of sound. The pulses bounce off of an object and the bat listens to the return sound to identify how close they are to it. If the object is a prey item, the bat will continue flying towards the object. The closer they get, called the approach, the quicker the pulses since there is less distance between the bat and its prey. As they hone in on the prey, the pulses get so close together it is nearly impossible to distinguish between pulses. We call these feeding buzzes when we are analyzing the calls.
But bats use ultrasonic vocalizations for more than foraging. It provides them a way to navigate in the night so they don’t run into things. It allows mother bats to identify their babies in a cave filled with thousands of individuals.
Each species of bat has a slightly different call (Ref. 3). When we analyze calls we can use spectrograms, or graphs of calls, to know what species we recorded. The call shape, frequency, and length all help to identify what species made that call. Using bat calls, we can study bat activity either as a large group or by individual species.
Spectrograph of bat calls; image courtesy UNCG Bat & Mouse Lab
In an urban setting, human activity and presence increases on the weekends, particularly Friday and Saturday evenings. Researchers have shown that wildlife will alter their behavior in response to human activity. Humans don’t have to directly interact with wildlife for wildlife to be impacted by people. The increase in human activity on the weekends has been deemed the weekend effect. The GSC along with researchers at UNCG wanted to determine whether the weekend effect impacted bats in Greensboro.
For more than two years, we collected bat calls at the GSC and UNCG, knowing the same species are found in both locations. The UNCG detectors served as our urban setting and the GSC detectors were our rural sites. We looked at all total activity and species-specific activity to see if bats responded to human disturbances. Researchers analyzed more than 180,000 bat calls. Looking through all the calls, we found an interesting pattern. At the GSC, there were significantly more bat calls on Friday and Saturday compared with weekdays. In contrast, at UNCG, there were significantly fewer bat calls on Friday and Saturday than there were on weekdays. From this we were able to determine that the weekend effect impacts bats in Greensboro. When all variables were accounted for, the only difference weekend to weekday was human activity – and it appears bats are responding to that by increasing their time in rural settings on the busy weekend nights and avoiding downtown. Parks and green spaces just outside of downtown are biological hotspots and havens for wildlife. As we saw, bats make great use of the green spaces around the GSC, particularly on the weekends. This information lets us make informed decisions on park designs and their uses by wildlife.
Just by passively recording animal calls we can learn about animal activity and behaviors. We will continue to record bats at UNCG and the GSC for research. We can use that data to answer a variety of scientific questions.
Thank you for your support of the GSC and, in turn, our research. We will continue to study wildlife and how it is impacted by people so that we can make smart decisions on environmental changes.
The GSC would like to thank the UNCG researchers and students who worked on this project.
Link to the full publication: https://doi.org/10.3390/ani10091636