No survivors in the nest. What did mama duck do wrong?

[chicks & ducks]

Hi all.

I recently posted here because our mama duck had some eggs in her nest that were a different color(transparent looking with dark spots) compared to the others. Candled the odd looking ones and they were bad. Did find 1 with a lil duck moving inside so put the other eggs(that didn't look dark and transparent) back in the nest and left her alone. She started with 18-20 eggs in the nest and the other day(when I took photos and checked) she was down to maybe 12-15, by the time I got rid of the bad ones she was down to 6 or 7.
Today I was watching her run to the spring with something in her mouth! Worried it was a baby duck and she was freaking out(it IS her first time) I ran out. It turns out she was taking a crushed egg shell to the spring and then washing her mouth out(funny to watch) but now the nest is down to 4 eggs and! 2 of those have those same dark spots on them that the others had. I will candle them tonight but not holding my breath. I did notice the other day that a couple eggs had little cracks in them. Her nest is made of sticks(though she has plenty of straw/hay available to her) and I'm wondering if they were just too unforgiving for a nest? perhaps she was crushing them into the sticks when she moved them or something?


The ONLY good thing that's happened is our other female has started to build a proper nest now, hopefully will start sitting soon. She's found a nice soft spot in the hay though, so that's good.

Any thoughts on why the other eggs didn't make it?

 

[sourland]

By the time 18 or 20 eggs were in that nest, some of them might have been excessively old. 18 to 20 although not an impossibility to brood in temperate conditions is borderline too many for a hen to cover effectively . Hopefully next batch she will be more successful - she may lay another clutch this year.