Smaller Mammals
It has been reported that raccoons, minks, and weasels consume bats. These animals typically come across bats roosting, either accidentally or potentially by sniffing them out; thus, they are aware of the specific location of the bats. Many mammals consume bats when they can.
Raccoons, weasels, and minks all have a habit of climbing into bat roosts to devour the animals there when the bats are sleeping. Additionally, these mammals wait outside a bat roosting place, ready to attack bats coming in and going out of the roost. When they share habitat areas, some larger bats hunt smaller bats. Depending on the hunter's stealth abilities, a roost of bats can be quite simple to sneak up on. Weasels, minks, and raccoons all enjoy snatching bats directly out of their roosts.
It might seem a bit unfair, but it’s the circle of life. Smaller mammals like those just mentioned have also been known to wait outside the roost and pounce on bats when they come in and out. In fact, many mammals might find this easier than sneaking up on the roost.