The birds were all dead by the time the pest control company arrived. There was no chirping. They were not able to determine how the birds were getting in, but they will be back over the weekend to follow up on the issue.
So let's break this down sentence by sentence.
The birds were all dead. That is, birds, plural, and all, indicating quite a few (more than just two or three). So we had a mass grave up there above the ceiling tiles. Lovely.
There was no chirping. Not to be picky, but this is a bit of redundant information. Since ALL the BIRDS were DEAD.
They were not able to determine how the birds were getting in. Yeah, here's how that went:
Thing 1 on a ladder: How do you suppose they're getting in?
Thing 2 looking up at Thing 1: Dunno. Can you see anything up there?
Thing 1 on a ladder: Nope. Don't see holes or nuthin'.
Thing 2 looking up at Thing 1: Well, don't that beat all.
They will be back over the weekend to follow up on the issue. Translated to regular-speak: They aren't coming back unless we report more chirping, in which case they'll bring over a big sprayer filled with bird poison to kill them. Unless they don't get over here in time.
In which case the birds will be dead already. And how will they know that ALL the birds are DEAD?
You got it. No chirping.
In the meantime, I'll be curious to see if and how someone answers this question online.