|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.
To be able to breed, a creature must have separate
[FEMALE] castes. Genderless and one-gendered creatures are incapable of breeding. In addition, intelligent creatures must be married or otherwise "marriage-compatible", even if they do not actually marry ingame.
When a compatible male and an uncaged female of the same species are on adjacent tiles, they'll breed when idle.
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. Pregnant non-egglaying females can give birth in cages, but not get pregnant again
Limits on breeding
Excluding your fortress citizens, there is a per-creature-type population cap of 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.
All non-sentient animals have a gestation period of 6 months (your citizens are 9 months), but there are several factors that can prevent them from breeding:
1. Too many adults - if you have more than 50 per species, they will stop breeding.
2. Too many children - if more than 75% of that animal's population is juvenile, they will stop breeding until the young ones grow up.
3. They're not interested - the animals in your "breeding pairs" are homosexual or otherwise uninterested in reproducing, which is the case for 5% of all animals.
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).
As non-historical non-pet fully-sentient figures cannot breed, visitors are more often able to breed than invaders, though this is countered by their relatively common separation from loved ones by distance or death.