Gaps in Fireplace Stonework

Hello! I have a question about 4 gaps in our stone fireplace (circled in the second picture). When we first noticed them after moving in, I assumed they were intentional to help vent heat into the room. Now, though, they feel very drafty, and we've actually had a few bats in the house that we think came through the gaps.

I wanted to see if they are intentional/serve a purpose; and if we would make the fireplace unusable if we fill the gaps in.

Thank you!