Ah, late July in Minnesota: Almost warm enough to prevent the bats from starving

Cold weather, fewer bugs lead to bat problems

When Jaime Edwards got to work on July 29 after several days of unusually cool summer temperatures, she had four voice mails about bats seeming weak, perching in odd places or even dead on the ground.

Within a few days, the Department of Natural Resources regional non-game expert had received maybe 10 more calls. Wildlife officials and conservation officers got even more calls..."...People are reporting finding two to three dead bats, with one report of up to 10 bats found dead in the yard..."
...
She suspects the culprit was the odd cold snap. With highs barely in the 60s and lows dipping into the 40s, the daily average temperature was as low as 16 degrees below normal.

Bats feast on insects, some eating their weight in mosquitoes, gnats and flies during a night before going back to roost around sunrise, she said. But with the cold, the bugs weren't coming out. She suspects the bats were hungry.