Near the town of Wee Jasper, about one hour from Canberra, there is a cave. For a few months a year, this cave fills with bats as they give birth and raise their young. Scientists would love to know how many bats are in the cave, but it turns out that counting these bats isn’t easy.
Scientists could try going in and counting the bats, but the bats don’t like being disturbed and could be hurt. Also, the cave is filled with toxic spores produced by a fungus that lives in bat poo.
Dr Doug Mills tried to count each bat as it flew out of the cave to hunt. He found it impossible to count them this way – they were leaving too fast and he couldn’t keep up.
Doug then used an infra-red video camera and computer software to record and count the bats leaving the cave. But Doug wasn’t sure whether the camera and the software counted the bats correctly.
To check the results from the computer, Doug played back the video in slow motion and counted the bats individually. It took him 15 hours to count the bats in just one and a half hours of video! He checked several nights’ worth of video and worked out that the computer counted a similar number of bats to his own counts.
Doug also wanted to find out how good he was at counting bats. He counted the bats in one video several times over and compared the numbers he got. He didn’t always get the same number, but they were very close, so he was probably quite accurate with his counting.
When he put all these bits of information together, he had an idea of how accurate the computer was at counting bats. Using this information, Doug can now count bats much more easily. And importantly, he knows when a change in bat numbers might just be a miscount, and when it’s big enough to worry about.