I usually embark with 10 female ducks and two male ducks. I always create a pasture where all of my ducks (both male and female) live. Almost all of my female ducks lay fertile eggs when they first arrive, but they only seem to lay non fertile eggs after that. What do I need to do to get them to lay fertile eggs?

Update and further details: I just created a large open (but indoor) pasture room with many nest-boxes installed in the pasture area and all of my male and female ducks pastured in it. I have more than a dozen each of both sexes. I have forbidden the door to the pasture room so my dwarves are not disturbing the eggs after they are laid in the boxes. I am running the 2014 version of DF. I then let the game run a few seasons; The females are laying many non-fertile eggs in the nest-boxes; apparently the males are still having problems fertilizing the eggs.

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    @KutuluMike: How would you pen them incorrectly? I assumed putting both sexes together in the same (open tile/non separated) pasture would be sufficient to allow them to breed. I understand it is possible to define a pasture that spans multiple rooms with closed doors, but that's not what I did. Commented Jun 12, 2016 at 12:01
  • @KutuluMike: you may have identified the problem. My pasture does not include my nest boxes. I assumed fertilization occurred prior to egg laying, not after. If this is the case, I invite you to submit an answer to this question. Commented Jun 12, 2016 at 12:06

2 Answers 2


As I understand it, at least in the latest version of DF, the male birds have to be able to reach the eggs in order to fertilize them, not the hens that lay them. It's counter-intuitive, since that's not how bird biology really works, but it is the behavior as of v.43.x. This is an "improvement" over earlier versions, where the males didn't even need to get anywhere near the hens or eggs (thanks @Iker) to fertilize them.

Make sure your male birds can reach the nest boxes -- put the boxes in the pasture with the other birds, for example. Your hens should wander over and lay eggs, then a tom/rooster/etc will follow behind and fertilize them.

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    Along with this, you need to make sure the dwarfs don't collect the eggs from the nest boxes, before or after fertilization. The best way to achieve this is to just to forbid the eggs as soon as they are laid. Commented Jun 12, 2016 at 12:40
  • I believe if you turn off "cooking eggs" in the Kitchen menu they won't collect eggs either.
    – KutuluMike
    Commented Jun 12, 2016 at 13:33
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    In earlier versions everything reproduced by spores, IIRC. As in, the male only had to be present somewhere in the map, and didn't even need to be able to path to the female.
    – Iker
    Commented Jun 12, 2016 at 21:02

I found the following on the DF Wiki page on breeding:

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.

This is the reason why my ducks are not laying fertile eggs; I already had a bunch of them from their reproduction during the beginning of my embark and due to the species cap they are now only laying infertile eggs. Knowing this, I now know that it is safe to butcher some of them and the remainder should then lay fertile eggs to replace their numbers.

Since this population cap is per species, during future embarks I will buy a breeding pair of every type of egg laying birds (turkeys, ducks, chickens, blue peafowl, guineafowl) to allow maximum egglaying population later on.

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