Well be prepared, Candle them 4 days before and again 3 days before due date as soon as you see the air cell dipping, LOCK THEM UP. they may dip the 5th day before due date..so you may want to candle them each day on the last week before hatching..
I didn't pay attention to the dipping of the air cell so I beleive thats where some of my problems may have occurred because I didn't lock them down when they were ready...So therefore they struggled..
I just stuck with 3 days before due date rule well with ducks you kind of got to go by there schedule and when they are ready, they are ready.. So look for the dipping of the air cell..
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I had my humidity up to 70 75 on lockdown. On due date I did make each remaining ones a Safe hole.
Calls ducks have such problems because of there little beaks and small necks. But when they come out and fluff up, makes you wander, how the hell did you fit in the egg. LOL..
I still beat myself for not being there for the one that zipped...But when it's 2 in the morning and you have to get up to go to work. just can't always do it..
Also listen for the peeping, try to locate it, one of mine the one with the most yellow on his beak, I could hear him at the wrong end that's how I knew he was upside down and going to need help..
THERE ONE VERY IMPORTANT THING:: THIS IS THE TOP PRIORITY: THEY ARE MESSY. don't be surprise if they follow you around when they are young but as soon as they are outside permanently, they are scared to death of you.... Don't let them swim the first week they are born, they can drown if not watched. Mommy ducks put an oil on baby ducks and since we don't have that capabilty, they need to wait and produce there own..
GOOD LUCK and I hope some of this helps...