I don't think there are many predators that could catch or kill a bat. You should probably contact your city animal control to report it. Bats are known to carry rabies, and that could be what's killing them. If they are not rabid, it's probably some other disease or parasite. Best to have it checked out. They will probably want the bodies for testing.

It could also be that the bats are being poisoned by pesticides, perhaps eating insects that have been sprayed with pesticides. I'd still check with the city to be sure, though.

Dead bats are not a good thing! Report it right away and keep the bodies.

Do you have any frogs in your pond?

I had a huge (size of my fist) (and I am not a small guy) frog in my pond who liked to take down and eat small birds! The problem was he could also take down birds larger then he could eat.

I knew it was him when I fished out a dead bird one night and left it pond side. The next morning it was back in the water, and the only predator around who might do that was green and was a great jumper.

I forgot to mention that the stomachs are eaten out on the dead bats. I have reported this (last year) to animal control, but they didn't seem concerned and told me rabies was not a problem in this area. We do have a Mosquito Abatement agency in this small mt. town, and I was wondering since bats eat mosquitoes if the mosquitoes could be weakened from the pesticide and then slowed down and raccoons could then catch them? We definitely have raccoons that come at night to the pond.
I thank you for all your responses, and no, erniem, I don't have any frogs, and I'm not sure why, but sounds like you have an interesting frog--Do you have fish? Thanks again to all of you

Maybe a weasel or mink? They are fast enough to catch a bat. They kill and eat meat. They are smart enough to wait at the pond at night, expecting the bats to come for dinner. Shut the pond lights off for a few days and see what happens. The bats are coming in for the bugs that are attracted to the lights maybe???

I don't think bats come that close to the ground to be caught by frogs or animals.
That's really disconcerting that they're dying. Call the DNR. That's a real bummer. Bats are wonderful beings.

That is just bizarre....sad and bizarre.

When I was a kid we had an outside cat who would place dead birds at the door. The stomachs would be eaten out but the rest of the bird intact. Any cats in the area? The bats that frequent my yard frequently fly low to get the insects hovering over the pond water and some have even brushed my arms while I sit at the bench. Wonder if there is a kitty at large.