Do Michigan Bats Avoid Moonlight?

This past fall, I was able to conduct an acoustics survey to find out if Michigan bats, specifically bats found in Oakland County, show evidence of lunar phobia. Lunar phobia is the avoidance of moonlight and has been observed in other mammals, insects, and birds. It can be caused by an increased predation risk (no one wants to be eaten) or prey availability. So who should care if bats avoid moonlight? Since bats are a crucial part of our ecosystem, my answer is: everyone should!

The more we are able to learn about Michigan bats, the better we will understand them and the better we will be able to help them face specific threats such as White-nose Syndrome, habitat destruction, wind turbines, and pesticides. It’s important to remember that we need our bats just as much as they need us! Michigan bats eat their entire body weight in insects each night, saving billions of dollars each year for the agricultural industry in the United States. By studying bats, scientists are also able to make improvements in flight and solar technologies. In regards to a bats preference towards moon illumination, if scientists know when bats are most active, perhaps wind turbines can be turned off during times of high activity.

The acoustics monitor SM3BAT from Wildlife Acoustics was used to collect high frequency echolocation calls from free-flying bats. The SM3BAT monitor was stationed to a tree on Rochester College’s campus in Oakland County, Michigan from July 2016 to November 2016 where it diligently collected calls for me while all I had to do was change the batteries! It made collecting data simple and it did not disturb the bats or other wildlife.

After I had my data, I used the Wildlife Acoustics Kaleidoscope Viewer to analyze and count the echolocation calls. The SM3BAT picked up six of Michigan’s nine bat species: Eastern Red bat, Northern Long-eared bat, Little Brown bat, Hoary bat, Big Brown bat, and Silver-haired bat. Bat echolocation calls look different depending on the species. This is because each species emits a call at a slightly different frequency; however, even within the species, the calls can vary! This can pose a challenge when trying to identify who’s been flying near my monitor. For this reason, I decided to group together Big Brown bats with Silver-haired bats and Northern Long-eared bats with Little Brown bats.

Once identified, the amount of bat calls from each group was compared to moon phases. Since other conditions were not taken into account (i.e. weather, cloud coverage), three days were chosen each month to represent a full moon and three days for a new moon. The full moon cycles were chosen when moon visibility was between 98-100%; new moon cycles were chosen when moon visibility was between 0-1%. This way, if it happened to be overcast during a full moon, there would be two other days to compensate.

Now, back to the question: do bats in Oakland County, Michigan avoid moonlight? The results from my study came back mixed! The Big Brown bat and Silver-haired bat group did not seem to show anypreference towards or against moon illumination. Though these two species were the most common bats found on the Rochester College campus, some nights showed more activity (more bat echolocation calls) than others and the moon phase did not appear to have any effect. On the other hand, the Northern Long-eared bat and Little Brown bat group and the Eastern Red bats did in fact show trends towards avoiding the moonlight. This supported my hypothesis, so I was excited with this news. Last but not least, the Hoary bats showed statistically significant evidence of being more active during a new moon than a full moon. Though there are trends to bat activity and moon phases, it’s important to remember that there may be other factors in determining when bats are more likely to be out flying and hunting.

I would like thank Rob Mies and the Organization for Bat Conservation for allowing me to use the Wildlife Acoustics SM3BAT, and Echo Meter Touch. The study could not have been done without such generous support.

– Jenna Orr, Education Specialist and Animal Keeper at OBC






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  • Dick Quantrille

    The question of bats avoiding moonlight is thought provoking. Since we have so few bats where I live and we will probably not have any flying insects for them to eat until late April, we might not see any bats this year. I still plan to put up my bat house as soon as it stops raining. Maybe in a week or so I hope.

    Thanks !

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