Strange! Nice to see that you figured it out, though!
I know that this isn't the same problem that you had, but since this IS a "Vanishing Animal" thread, I was wondering if anyone else has had THIS happen to them: I had a male Gorilla vanish on me WHILE I WAS PLAYING THE GAME! I suddenly got a message in my message bar that Kong's mate was upset about her lack of a partner, and when I whent to check, he had not just vanished from the exhibit itself but also from ALL the different animal lists!! He hadn't died (he & KoKo had been happy & healthy the month before) and he wasn't on the loose. He was just gone! The only thing that saved him (and makes this even stranger) was that waaaay back in my message bar was a message I had from when I was first creating the exhibit (he was upset about something or other) and when I clicked on it, *** POOF *** darned if he didn't just re-appear!
This has never happened before or since.
Anyway, I feel better just talking about it....
-ZW