how to make a bull roarer and does it call bats?

Answer 1

Bull roarers were used by Australian Aboriginals as a form of communication and ceremonial tool. Basically, the bull roarer is a shaped piece of wood that is attached to a long length of string or twine. When whirled around the the head, the wood rotates and makes a whirring noise.
So, it is quite possible that a bat could be attracted to the noise, or using the sonar effect of the call, home in on the whirling piece of wood. I have seen children throw a nut and bolt screwed together with a piece of paper into the air and attract bats. The paper fluttered and made a noise, the bolt and nut had mass. The bats went mad trying to catch the bolt and nut. Probably made the same sort of noise, to the bat, as a big juicy moth.
So I guess the bull roarer could have been used to attract bats, although I have never heard of Aboriginals eating bats.

Answer 2

the question is a bit unclear.