By: Trina Morris, GA DNR Wildlife Biologist
It’s that time of year again. The time of year when many kinds of wildlife are giving birth and raising young. Bats are no exception.
Female bats often come out of hibernation pregnant. While bats breed in the fall, females are able to delay fertilization until the spring. Depending on the area of the state, females usually give birth in May or June.
Some species raise young in maternity colonies which can be under bark, in hollow trees, in structures, crevices and other areas. Each year biologists from the Georgia Department of Natural Resources’ Wildlife Resources Division count maternity colonies of gray bats (Myotis grisescens) and southeastern bats (Myotis austroriparius) in caves.
These species hibernate in caves and move to warmer caves in the summer to raise young. Unlike other species that move into smaller colonies across the landscape, the cave dependent species cluster into only a few sites across the state, making this time of year the perfect time for counting them.
It’s not as easy as it sounds. Bats fly out of their caves at dusk quickly and erratically. In the past, numbers have been estimated by counting for one minute out of each five until the emergence ended. Then the numbers were extrapolated to estimate the count each year. That method was not the most accurate and was soon replaced by video counts.
The first video counts used infrared lights and cameras in night shot mode to film the emergence. This method still involved visually counting the bats on the tapes, which was labor intensive and difficult. Recently a new method has been developed. The U.S. Army Corps of Engineers developed a system using thermal cameras to record bats and custom software to count them.
The process still requires some work to make sure the counts are correct and consistent from year to year. However, this method is less time intensive and hopefully, a lot more accurate. Additionally, the camera allows you to see the bats in the dark. This video is an example of an emergence of southeastern bats in south Georgia.
During our counts of gray bats in north Georgia, we caught a couple bats by hand to verify the species and reproductive status. One female gray bat was pregnant and the other was lactating. That probably indicated that the young were just being born during the second week of June.
In the third week of the month, we traveled to south Georgia to count southeastern myotis. Nikki Castleberry from the Georgia Museum of Natural History pointed out that a bat had fallen on the ground at one site. As we watched more closely, we noticed lots of bats falling and running into each other. I had a suspicion that these were young bats just learning to fly.
I managed to catch one and verify just that! One week after young were being born in north Georgia, baby bats were beginning to fly in the southern part of the state. The bats normally begin their maternity season sooner the further south you travel, but bats are beginning to fly all over the state now. They’re not great flyers at first and, like birds, they often need a little practice leaving them more vulnerable to predators and injury.
DNR receives many phone calls this time of year from people with bats in their homes. In most cases, numbers are small and the problem isn’t urgent. Most species of bats only give birth to one pup a year, and the pups are vulnerable to changes in temperature and completely dependent on their mothers for the first weeks of their life.
If homeowners exclude the mother bats when the young can’t fly, the young will die. Unless the situation is threatening to the health of homeowners, we recommend avoiding exclusions between May and August. If the problem can’t wait, call a Georgia licensed nuisance wildlife company in your area.
DNR also receives a lot of calls about baby bats falling out of roosts. It is not uncommon to see some mortality at roost sites, since pups are more susceptible to changing temperatures and environmental conditions. If a small number are found dead, it’s probably not something to be alarmed about. If large numbers of bats are dying in your area, it could be a sign that something is wrong.
As with many other animals, this is an important time of year for bats. By the end of the summer, we won’t be able to tell pups and adults apart. Bats grow fast and start consuming large amounts of insects as soon as possible. Give them a little time to grow up this summer. Watch your yard and see if you notice any bad fliers on the landscape. That might just be a young bat, learning to use its wings for the first time. Let’s hope this year’s bats survive to eat insects for many years to come.