Looks like they ran across this during a demolition. Is this something you see often?

Nope, but it's looks similar to a pile of freetails I once found dead and dying in the bottom of a metal bath exhaust vent duct.
Was that found in a similar situation? All piled up at the bottom with the sides to slick to climb out.

Hey Warrior, I just happened to run across this picture online, so not sure of the situation, but that makes sense to me.

Looks like a batch of Bat Brownies

Looks like there was a hole in the mortar between the tile and bats kept falling down in the chimney getting trapped . Yup seen that normally in the clean out but by the shape of that there wasn't a clean out

Folks often fail to realize that though bats can grasp most surfaces, slick metal or other slick surfaces can easily form pit traps.
I had a church 2 years ago when we first started, the metal firebox that keeps insulation back from the stove pipe in the attic, had
more than 200 bat skeletons and a few fresh dead ones in it. Picked them all out and gave them to the UNM museum folks for their
collection. Pallid bats, some yuma myotis and a good bunch of Mexican free-tailed.

Did a fire station last year where a bunch of MFT fell into metal wall voids, the result looked very similar as they couldn't escape.

Rough way to go..

I have heard of bric-a-brac, but that's the first picture I ever saw of a brick of bats.

If you kept it could be bric-a-brac.

Keith