I had one of my roosters loose an eye and I tried keeping him for a while but he was very fearful of anything on his blind side. Also he would accidentally kill baby chicks by stepping on them or running into them so I ate him. Your rooster might pull himself together after a while just keep him...
I say go for it, its good for them and they will love it. Just make sure to mash them up good so they don't recognize them as eggs or they might start eating them as soon as they lay them.
I think it would be better to stop turning earlier rather than later so that the ducks have time to orient themselves in the proper position. I have the opposite problem right now with a cat eating the developing eggs but not harming the broody hens.
Oops I just realized you are talking about duck eggs... If they are anything like chicken eggs then I guess you could stop turning them earlier than usual but I have never hatched duck eggs before. Sorry about that.
They breed year round and they can hatch during the winter but usually hens don't go broody during the winter. My old english game bantam hen hatched a clutch in december but that was the only time any of mine went broody in the winter.
they lay 160-180 eggs per year and they are very good for eating although they are not full on meat birds like cornish crosses. I have one and it has hatched eggs 3 times within the past year.
I would say it was Raccoons If you live in North America.
http://www.avianaquamiser.com/posts/What_killed_my_chicken__63__/
One of these dog-proof traps will catch raccoons and possums. Hopefully the other 2 are hiding somewhere and ok.
I have always had better luck when I take them out of the turner and lay them flat on their sides on day 18. Normally you would put water in the tray for the entire incubation process and on day 18-21 you would put even more water so the humidity goes up. If you live in a very humid area like I...
It will take time for the original hens to accept the new hens. You could separate the new hens within the coop so they will be safe from the other hens yet still within sight until they get used to each other. When I brought a new hen to my flock it took 6 months for the others to stop picking...
They make very strange noises when they are first learning to crow - squeaks and groans and gurgles and burps ect. Sometimes hens will crow if there is no rooster around. The tail feathers look like a rooster but I cant tell with the hackle feathers. Lift up the feathers on its back and look...
These might help http://icwdm.org/inspection/livestock.asp
http://www.avianaquamiser.com/posts/What_killed_my_chicken__63__/
If the abdomen was eaten I would guess a possum did it. A duke dog-proof trap baited with sardines will catch many possums and racoons. Been there, sorry about your hen.
Buy a couple baby chicks to keep it company! Try to get some that are roughly the same age as it because they are social creatures and will do better with others to hang out with.