When a clan thins their numbers by mass killing unwanted koyukkuris (unwanted adults usually get exiled instead).
Unwanted koyukkuris generally consist of:
- Spoiled brats / shitheads that are deemed to be undisciplinable
- A ko that killed another yukkuri (usually her own sister)
- Excess kos in pregnancies if the clan limits the amount of kos each family can have (usually because of food constraints)
- Premature yukkuris
Killing of yukkuris are deemed uneasy by yukkuris so in clans that practice culling, there's usually a single dedicated "executor" yukkuri who's the only member of the clan permitted to perform these executions.
Culling is sometimes also practiced by pet yukkuris whom owner limits the amount of children they're allowed to have