So I suddenly get a message about a missing dwarf. I can't figure out where he is, so I go looking if he got in any mischief in announcements that I missed among the cancellation spam and the recent discovery of the magma sea and all the sudden mineral discoveries this triggers, seemingly out of nowhere as I hadn't breached anything.

These keas are miserable creatures and have been continually stealing things. Since I beefed up the security at what is now the only entrance it's mostly just stray bolts (that have mostly been shot at previous keas). But surely they can't kill a dwarf, right?
Still the times are right.

The kea message.

The missing message.
So I check combat logs.

Uh-oh. That's kind of ominous. Where did this happen?

Double uh-oh. Guess what's right under that open space? You've probably figured this out already.

Yeah.
Remember that magma sea discovery? I guess we have an explanation for that too. Semper fi, Sigun Olonlegon, bird fighter and explorer.