A handful of studies have observed that bats suffer from predation by snakes and birds of prey, which sit and wait for them to leave their roosts at night......

Bats are clever animals though, and may have evolved strategies to evade such attacks.

They can roost by themselves, but often they can be found in large groups all huddled together in a tree cavity, or hollow. They also switch which areas they roost in, and many switch trees or switch cavities every few nights.

As you could imagine, large groups of animals all sleeping and defecating in the same place every night makes for a very smelly bed!

And that smell is all the information predators such a black rats (Rattus rattus), foxes and cats, need to work out exactly where to sit and wait to prey upon bats.

(Rattus rattus!!)

.....

We wanted to test the idea that bats roosting alone, rather than in groups, would not attract as much unwanted attention, and bats switching roosts every day also did not attract as much attention as those that stayed in their roosts for multiple days.

.....

I found that common urban species including the black rat and the ringtail possum (Pseudocheirus peregrinus) were quickly attracted to even small amounts of bat poo.

This means that bats roosting alone, rather than in groups, are more vulnerable to predation at their roost.

In addition to this, we found no effect of switching, so bats trying to evade predation by moving roosts every few days may still be found by scent-seeking predators.

Wouldn't flying be advantageous to evading predation? Rats, foxes, and cats can't fly...

You snooze, you lose.

Then the key is not to snooze.

pack animals migrate in herds so as to reduce their odds in an attack. it's safety. same for how bats sleep.

Safety because if I'm in a pack of 100 chances are good I can outfly some of the weaker pack members?