A census of bats hibernating in the Sodalis Nature Preserve mines in Hannibal is scheduled for Wednesday.
Shauna Marquardt of the U.S. Fish and Wildlife Service said Tuesday that people from across the Midwest will be participating in the count.
In advance of the census, a maintenance crew from the Hannibal Parks and Recreation Department checked the gates to assure access to the mines would not pose a problem for the teams of bat counters.
"We've had trouble in years past with the gates being frozen over," said Mary Lynne Richards of the parks department. "Today were making sure they (gates) can be opened up and that the locks are working properly."
The bat count at Sodalis is held every two years. The last census occurred in February, 2017, with approximately 40 people enter the mines for around four hours. It was found that the number of federally endangered Indiana bats had risen from 167,000 to 211,000.
"They were very happy because the numbers went up," Richards said. "We did not know if the bats would stay around, but they have. It's kind of exciting."
While the number of Indiana bats went up, there was a decline in gray bats and northern long eared bats, both of which are either federally endangered or threatened.
Marquardt said white nose syndrome was likely to blame for the lower numbers of other bat species.