Pretty self explanatory, right?
I was trying to see if killing off the dwarves in adventure mode would result in the same situation as if they died off during worldgen- a fortress with no diplomatic contacts or immigrants- but it was taking me a while. There was only one mountain fortress, but it held 108 dwarves, and about a third of them knew how to use crossbows.
My strategy was to send in a dwarven adventurer with maxed out spear skills, stab a crossbowdwarf in the head, die in a hail of boltfire, and repeat.
About 20 or so adventurers in I began to notice something odd- there were a lot of combat reports involving goats mauling children. I thought this was unusual, but not that unlikely, until one of my adventurers spawned pretty far away from the fortress in the middle of a herd goats that stretched as far as the eye could see.
I also began to notice that with each subsequent adventurer the map took longer and longer to load- I thought this had been because of the increasing quantities of gear strewn about but far more likely it has something to do with the exponential increase in goats each time I visit.
Currently it takes about five minutes to load, and generates about a page of combat reports each step I take.
So basically, repeatedly setting out with an adventurer does something weird to the wildlife. Like it generates the usual five goats each time but saves all the old ones or something. (There were armies of Hoary Marmots too, but not anywhere near as many as there were goats.)
And while you're here, are dwarves whose civilization was wiped out in world gen really not supposed to have any diplomacy? I didn't get any human merchants or even kobold thieves in the several years that I played.