Well, In terms of relative scouting usefulness, I think it is worth keeping in mind that if an owl shows up and flies around checking things out, I’d have to say that most people ought to think “Ah, a familiar”. Owls simply don’t behave that way. Bats, on the other hand, do. There is no reason a bat scout would be suspicious under most circumstances. Underground or indoors, this is hugely magnified- there is just little likelihood of a normal owl appearing in such places. Yes, the odd barn owl, but they don’t fly around inside the way a bat may, and they are pretty unlikely to appear in caves, where again the bat is probably one of many.
Perhaps, in caverns, the familiar could trigger a swarm of bats at an opportune moment?
Perhaps, in caverns, the familiar could trigger a swarm of bats at an opportune moment?