It's typical of most birds during the winter. Fertility goes down. Ducks specifically molt and eggs aren't fertile when they are in molt.
My problem may have been shipping though. The eggs were all sent 2 day priority but didn't arrive for 4 days, and one batch 7 days,
Interesting. I assumed they were like my chickens, when they molt they stop laying, once they start laying again the eggs have been fertile. The laying dropped off while they were molting, I figured what they were laying would be fertile. My bad
