They don't know. It's bleeding edge science and so far the study was only done for bats. Likely other scientists will look into birds now. Birds are only very

They don't know. It's bleeding edge science and so far the study was only done for bats. Likely other scientists will look into birds now. Birds are only very distantly related to bats (hundreds of millions of years away in evolutionary time) and their last common ancestors didn't fly. There's something called convergent evolution when you have similar problems you come up independently with similar solutions, but then birds are in many ways very different from bats. So it could be that they have a similar mechanism, or they get around the problem in some other way.