I am learning something from this too..First yes a good broody chicken will sit for the 4 weeks on duck eggs. If the eggs were layed within the last 2 weeks and kept at 50- 60 they should hatch. If they were kept cooler or warmer they still have a good chance. Some on BYC had experiments going with this on chickens. I don't know their percentages, but chicks did hatch.