|This article is about the current version of DF.|
Breeding creatures are those which can produce offspring in fortress mode. Conversely, non-breeding creatures cannot reproduce in fortress mode, even though they presumably do so during worldgen. Breeding creatures are significantly more useful as stock for a meat industry than their non-breeding counterparts.
Currently the tokens necessary for breeding are not known. Toady stated that he "removed requirement that a creature have a baby/child state to breed completely" in version 0.40.06, however there are presumably other requirements (such as having a female gender).
When a compatible male and a female of the same species are present on the map, sooner or later they will breed. To do so, they will need to be situated on adjacent tiles. Breeding can be prevented by gelding males, separating males and females, caging females, or while (non-aquatic?) creatures are swimming. Caged males are still capable of breeding, assuming the female can approach the cage.
Invaders normally are incapable of breeding, but they have been observed to arrive on the map pregnant. Additionally, invaders (whether soldiers or mounts) can become pregnant and breed while on the map if they possess the
[PET_EXOTIC] tokens (and a
[PET_VALUE]), but their parents will immediately attack their offspring unless they are separated from each other (such as via cage traps).
There is a per-creature-type population cap, observed to be around 50, past which breeding animals will not get pregnant; existing pregnancies will mature to term. Furthermore, animals will not reproduce if children make up more than 75% of their population - for creatures which take longer than a year to grow up (such as elephants, which take 10 years), this can slow breeding significantly. Once the population drops below these caps, the creatures will begin breeding again.