The bats become very active just after dark when the mosquitoes are most active. The population in our area is very large, and there may be more this year since the mosquito population seems to have boomed.
Don’t do anything to harm them – a single bat can eat a thousand mosquitoes per hour.
There are bat detectors available that convert their sound down to an audible range – a former neighbor used to bring one up. They may be available for rent or to borrow. Check with the wildlife centers for information.