Ah, an excellent thread, this one. Contains a lot of information that is all too often ignored or otherwise overlooked. I do have a couple of things to add to this though.
Some caveats: Creatures with UTTERANCES, or without the ability to speak, will always be hostile, even if they technically would be considered the same faction. They will also wage endless wars, since they lack the ability to form treaties.
Regarding this, UTTERANCES on its own does not have this effect. It is solely whether or not the creature can speak or not. I have been playing with a custom species for over 3 years now that has both UTTERANCES and INTELLIGENT and the only effect it has is that said species use the kobold's gibberish for all their naming needs. They otherwise act just like any other civ.
MAX_SITE_POP_NUMBER places an approximate limit on the number of individuals that can live in a site. The closer a site is to reaching its limit, the more likely it is for a new site to be created.
It is my experience that this token no longer has any effect, or at least one that is difficult for me to notice.
Note that this doesn't fully apply for civs with DEFAULT_SITE_TYPE:CAVE, as these civs will never build new sites, only settle in existing caves. If a civ has no nearby cave for migrants to move into, they will remain in place.
This is not entirely true. While in world gen a civ with DEFAULT_SITE_TYPE:CAVE will not settle in any other caves than the one they are placed in at the start of world gen. After world gen they will go and "reclaim" other caves, but if the cave is on a different landmass (or in some other way inaccessible?) the group will just sit in place and go nowhere. This "reclaiming" of caves will often have the effect of emptying the original cave of most of its inhabitants.
Furthermore, in the event that there are no empty caves to "reclaim" the civ will instead send out one or more groups to "found" a new cave. This will create a large site that contains nothing at all, which on the adventure map resemble what dwarf sites used to look like before that last major update made them visitable again. And just like those unvisitable dwarf sites, there will be no way to find or in any way interact with those said to live there.
Do note though that I noticed said effects with my own custom species, I am not sure if creatures lacking INTELLIGENT (such as kobolds) will engage in such silly behavior, though I suspect they might.
Civs with [DEFAULT_SITE_TYPE:CAVE] will not create their own sites, and will not appear on the civ list in fortress mode. They will, however, settle in other sites and may go to war with other civs, provided they have the required tags. This allows you to create 'secret' civs that may show up as a surprise for a fort, or you may rarely find members of them hanging out on regular sites as an adventurer. On rare occasions, a cave civ may take over a nearby settlement and claim it for themselves.
Adventurers can come from cave civs, but you will not be able to see where they start out on the map when choosing your adventurer.
Regarding not creating their own sites, see above. Regarding not being able to see cave civ's adventurer's origins, I should add that that is entirely dependent on where you have "reveal caves" set on or off. (it is off by default)
Thanks a lot for this thread, IndigoFenix. I, for one, did not know that making a CAVE_DETAILED site in non-mountain site makes the settlements into hillocks. I for some reason thought it was "SETTLEMENT_BIOME" responsible for that.
Now I can have tribals living in mud huts. And a few other things were either refreshing or interesting as well, so thanks a lot again.
Lastly, I should add that while
most of the settlements with this will be hillocks, a few of the civs settlements(and always the first one) will be a fortress, regardless of what biome it is in. In this manner it mimics the way towns and hamlets work.