Adding a nest similar to the one from environmental seems to be a popular request.

Not sure if I really want to implement it though since it may make farming too easy.
Also making ducks and geese able to breed automatically could introduce lag in longer running worlds.

Suggested in #23 and #7

I don't know if the mod I use is the same as Quark's one! It is by someone called Slexom; I don't think Quark is available for Fabric.

I know absolutely nothing about the internals of minecraft mods so maybe this is an untenable idea, but could you just have it require the bedding to be added, and consumed, in the exact same way as seeds are in a/the trough? (ETA: As in 1 feather/whatever consumed per bird interacting with it?)

I realise I'm just a random passer-by, but I have your mod (love it, thanks) and also 'animal feeding trough' (amongst many others) and a pen of ducks we breed using the trough. They do multiply rather rapidly, and I imagine if there wasn't the limitation of my needing to put one stack of seeds in at a time, it would become crazy really fast.

I considered automating the seeds being inserted into the trough, but after only a few hours of playing and occasionally dropping seeds in the trough I had well over 300 ducks in that pen. (I also have the uhhh, entity banners(?) mod that works a bit like terraria banners; and I got one for 100 ducks from promenade and the whole set up to 200 ducks from your mod when I did
a big cull).

So, nests might be cute, but I agree it might lag a long world out.. Maybe if you did, it should only breed the ducks if 'bedding' like grass, leaves, or feathers (suggestions based off the nesting behaviour of wild mallard ducks) is added by players, and this bedding gets consumed/wears out over time?

Yeah I think the quark feeding trough does check if there are already too much entites around it and won't breed and just consume the food. I think I probably could do something similar to avoid crowded nests. I also like the idea of building bedding like you described but that seems a bit more complicated than just checking if the area is too crowded.