I opened and cage-trapped a small entrance to the caverns. Through the years I trapped and tamed a cave crocodile, a giant olm, a giant toad and a giant cave spider. I modded them so they could breed and everything, and was very excited to breed and feed my dwarves solely on cavern creatures. These were the only ones I took, I didn't kill any of these species.
But as the years passed I got none of those creatures again, no breeding pairs. They literally never seemed to spawn in the area. I decided all the cavern creatures were spawning in other places of the cavern I couldn't see. Sure enough, I used df-hack's reveal command, and it showed cavern creatures spawning in different places of the caverns, but never again in my corner.
So I decided I would wall off all entrances to the cavern, all borders, except the border near my cage-trapped entrance. In this way, I would be able to control where cavern creatures spawn right? Well, I did it. But after walling off all of the cavern borders except mine, no more creatures are spawning. Occasionally one spawned in a little square I missed, so I would go and patch it up.
It's like the game is deliberately avoiding my border to spawn cavern animals. And now that everything is closed off except the entrance I left, no cavern creatures are spawning.
What is happening and how can I fix it? I would appreciate any help.